Receptor Concentration and Diffusivity Control Multivalent Binding of Sv40 to Membrane Bilayers

Oliwia M. Szklarczyk, Nélido González-Segredo, Philipp Kukura, Ariella Oppenheim, Daniel Choquet, Vahid Sandoghdar, Ari Helenius, Ivo F. Sbalzarini, Helge Ewers

Incoming Simian Virus 40 particles bind to their cellular receptor, the glycolipid GM1, in the plasma membrane and thereby induce membrane deformation beneath the virion leading to endocytosis and infection. Efficient membrane deformation depends on receptor lipid structure and the organization of binding sites on the internalizing particle. To determine the role of receptor diffusion, concentration and the number of receptors required for stable binding in this interaction, we analyze the binding of SV40 to GM1 in supported membrane bilayers by computational modeling based on experimental data. We measure the diffusion rates of SV40 virions in solution by fluorescence correlation spectroscopy and of the receptor in bilayers by single molecule tracking. Quartz-crystal microbalance with dissipation (QCM-D) is used to measure binding of SV40 virus-like particles to bilayers containing the viral receptor GM1. We develop a phenomenological stochastic dynamics model calibrated against this data, and use it to investigate the early events of virus attachment to lipid membranes. Our results indicate that SV40 requires at least 4 attached receptors to achieve stable binding. We moreover find that receptor diffusion is essential for the establishment of stable binding over the physiological range of receptor concentrations and that receptor concentration controls the mode of viral motion on the target membrane. Our results provide quantitative insight into the initial events of virus-host interaction at the nanoscopic level.

Cryogenic localization of single molecules with angstrom precision

Siegfried Weisenburger, Jing Bo, Alois Renn, Vahid Sandoghdar

The precision in localizing a molecule is ultimately determined by the number of detected photons, which is in turn limited by photobleaching. Currently, fluorophores can be routinely localized to a few tens of nanometers at room temperature. In this work we demonstrate localization precision better than 3 Angstrom by substantial improvement of the molecular photostability at cryogenic temperatures. We discuss the challenges, solutions and promise of our methodology for high-performance co-localization and super-resolution microscopy.

The quantum transverse-field Ising chain in circuit quantum electrodynamics: effects of disorder on the nonequilibrium dynamics

Oliver Viehmann, Jan von Delft, Florian Marquardt

We study several dynamical properties of a recently proposed implementation of the quantum transverse-field Ising chain in the framework of circuit quantum electrodynamics (QED). Particular emphasis is placed on the effects of disorder on the nonequilibrium behavior of the system. We show that small amounts of fabrication-induced disorder in the system parameters do not jeopardize the observation of previously predicted phenomena. Based on a numerical extraction of the mean free path of a wave packet in the system, we also provide a simple quantitative estimate for certain disorder effects on the nonequilibrium dynamics of the circuit QED quantum simulator. We discuss the transition from weak to strong disorder, characterized by the onset of Anderson localization of the system's wave functions, and the qualitatively different dynamics it leads to.

Observing the Nonequilibrium Dynamics of the Quantum Transverse-Field Ising Chain in Circuit QED

Oliver Viehmann, Jan von Delft, Florian Marquardt

We show how a quantum Ising spin chain in a time-dependent transverse magnetic field can be simulated and experimentally probed in the framework of circuit QED with current technology. The proposed setup provides a new platform for observing the nonequilibrium dynamics of interacting many-body systems. We calculate its spectrum to offer a guideline for its initial experimental characterization. We demonstrate that quench dynamics and the propagation of localized excitations can be observed with the proposed setup and discuss further possible applications and modifications of this circuit QED quantum simulator. DOI: 10.1103/PhysRevLett.110.030601

Applying contact to individual silicon nanowires using a dielectrophoresis (DEP)-based technique

Christian Leiterer, Gerald Broenstrup, Norbert Jahr, Matthias Urban, Cornelia Arnold, Silke Christiansen, Wolfgang Fritzsche

One major challenge for the technological use of nanostructures is the control of their electrical and optoelectronic properties. For that purpose, extensive research into the electrical characterization and therefore a fast and reliable way of contacting these structures are needed. Here, we report on a new, dielectrophoresis (DEP)-based technique, which enables to apply sufficient and reliable contact to individual nanostructures, like semiconducting nanowires (NW), easily and without the need for lithography. The DEP contacting technique presented in this article can be done without high-tech equipment and monitored in situ with an optical microscope. In the presented experiments, individual SiNWs are trapped and subsequently welded between two photolithographically pre-patterned electrodes by applying varying AC voltages to the electrodes. To proof the quality of these contacts, I-V curves, photoresponse and photoconductivity of a single SiNW were measured. Furthermore, the measured photoconductivity in dependence on the wavelength of illuminated light and was compared with calculations predicting the absorption spectra of an individual SiNW.

Spatio-spectral characteristics of parametric down-conversion in waveguide arrays

R. Kruse, F. Katzschmann, A. Christ, A. Schreiber, S. Wilhelm, K. Laiho, A. Gabris, C. S. Hamilton, I. Jex, et al.

High dimensional quantum states are of fundamental interest for quantum information processing. They give access to large Hilbert spaces and, in turn, enable the encoding of quantum information on multiple modes. One method to create such quantum states is parametric down-conversion (PDC) in waveguide arrays (WGAs) which allows for the creation of highly entangled photon pairs in controlled, easily accessible spatial modes, with unique spectral properties. In this paper we examine both theoretically and experimentally the PDC process in a lithium niobate WGA. We measure the spatial and spectral properties of the emitted photon pairs, revealing correlations between spectral and spatial degrees of freedom of the created photons. Our measurements show that, in contrast to prior theoretical approaches, spectrally dependent coupling effects have to be taken into account in the theory of PDC in WGAs. To interpret the results, we developed a theoretical model specifically taking into account spectrally dependent coupling effects, which further enables us to explore the capabilities and limitations for engineering the spatial correlations of the generated quantum states.

Transverse entanglement of biphotons

F. Just, A. Cavanna, M. V. Chekhova, G. Leuchs

We measure the transverse entanglement of photon pairs on their propagation from the near to the far field of spontaneous parametric down-conversion (SPDC). The Fedorov ratio, depending on the widths of conditional and unconditional intensity measurements, is shown to be only able to characterize entanglement in the near and far field zones of the source. Therefore we also follow a different approach. By evaluating the first-order coherence of a subsystem of the state we can quantify its entanglement. Unlike previous measurements, which determine the Fedorov ratio via intensity correlations, our setup is sensitive to both phase and modulus of the biphoton state and thus always grants experimental access to the full transverse entanglement of the SPDC state. It is shown theoretically that this scheme represents a direct measurement of the Schmidt number.

Nonlinear cross-Kerr quasiclassical dynamics

I. Rigas, A. B. Klimov, L. L. Sanchez-Soto, G. Leuchs

We study the quasiclassical dynamics of the cross-Kerr effect. In this approximation, the typical periodical revivals of the decorrelation between the two polarization modes disappear and remain entangled. By mapping the dynamics onto the Poincare space, we find simple conditions for polarization squeezing. When dissipation is taken into account, the shape of the states in such a space is not considerably modified, but their size is reduced.

Observation of modulationally unstable multi-wave mixing

J. Fatome, C. Finot, A. Armaroli, S. Trillo

We demonstrate experimentally that multiple four-wave mixing (FWM) pumped by a dual-frequency input in a single-mode fiber is modulationally unstable. This collective type of instability leads, in the anomalous dispersion regime, to sideband growth around all orders of FWM. This is in contrast with the normal dispersion regime where our measurements show that FWM exhibits no instability. Our conclusions are based on the first systematic mapping of the phenomenon as a function of the dual-pump input frequency separation. (C) 2013 Optical Society of America

Polariton excitation in epsilon-near-zero slabs: Transient trapping of slow light

Alessandro Ciattoni, Andrea Marini, Carlo Rizza, Michael Scalora, Fabio Biancalana

We numerically investigate the propagation of a spatially localized and quasimonochromatic electromagnetic pulse through a slab with a Lorentz dielectric response in the epsilon-near-zero regime, where the real part of the permittivity vanishes at the pulse carrier frequency. We show that the pulse is able to excite a set of virtual polariton modes supported by the slab, with the excitation undergoing a generally slow damping due to absorption and radiation leakage. Our numerical and analytical approaches indicate that in its transient dynamics the electromagnetic field displays the very same enhancement of the field component perpendicular to the slab, as in the monochromatic regime. The transient trapping is inherently accompanied by a significantly reduced group velocity ensuing from the small dielectric permittivity, thus providing an alternative platform for achieving control and manipulation of slow light.

SCATTERING OF AN EXPONENTIAL PULSE BY A SINGLE ATOM

Markus Sondermann, Gerd Leuchs

We discuss the scattering of a light pulse by a single atom in free space using a purely semi-classical framework. The atom is treated as a linear elastic scatterer allowing to treat each spectral component of the incident pulse separately. For an increasing exponential pulse with a dipole radiation pattern incident from full solid angle the spectrum resulting from interference of incident and scattered components is a decreasing exponential pulse.*

Observation of acoustically induced modulation instability in a Brillouin photonic crystal fiber laser

Birgit Stiller, Thibaut Sylvestre

We report the experimental observation of self-induced modulation instability (MI) in a Brillouin fiber laser made with a solid-core photonic crystal fiber (PCF) with strong anomalous dispersion. We identify this MI as the result of parametric amplification of optical sidebands generated by guided acoustic modes within the core of the PCF. It is further shown that MI leads to passive harmonic mode locking and to the generation of a picosecond pulse train at a repetition rate of 1.15 GHz which matches the acoustic frequency of the fundamental acoustic mode of the PCF. (C) 2013 Optical Society of America

Photonic crystal fibres for chemical sensing and photochemistry

Ana M. Cubillas, Sarah Unterkofler, Tijmen G. Euser, Bastian J. M. Etzold, Anita C. Jones, Peter J. Sadler, Peter Wasserscheid, Philip St. J. Russell

In this review, we introduce photonic crystal fibre as a novel optofluidic microdevice that can be employed as both a versatile chemical sensor and a highly efficient microreactor. We demonstrate that it provides an excellent platform in which light and chemical samples can strongly interact for quantitative spectroscopic analysis or photoactivation purposes. The use of photonic crystal fibre in photochemistry and sensing is discussed and recent results on gas and liquid sensing as well as on photochemical and catalytic reactions are reviewed. These developments demonstrate that the tight light confinement, enhanced light-matter interaction and reduced sample volume offered by photonic crystal fibre make it useful in a wide range of chemical applications.

Quantum versus classical polarization states: when multipoles count

L. L. Sanchez-Soto, A. B. Klimov, P. de la Hoz, G. Leuchs

We advocate a simple multipole expansion of the polarization density matrix. The resulting multipoles are used to construct bona fide quasiprobability distributions that appear as a sum of successive moments of the Stokes variables, the first one corresponding to the classical picture on the Poincare sphere. We employ the particular case of the Q function to formulate a whole hierarchy of measures that properly assess higher-order polarization correlations.

Full photon statistics of a light beam transmitted through an optomechanical system

Andreas Kronwald, Max Ludwig, Florian Marquardt

In this paper, we study the full statistics of photons transmitted through an optical cavity coupled to nanomechanical motion. We analyze the entire temporal evolution of the photon correlations, the Fano factor, and the effects of strong laser driving, all of which show pronounced features connected to the mechanical backaction. In the regime of single-photon strong coupling, this allows us to predict a transition from sub-Poissonian to super-Poissonian statistics for larger observation time intervals. Furthermore, we predict cascades of transmitted photons triggered by multiphoton transitions. In this regime, we observe Fano factors that are drastically enhanced due to the mechanical motion. DOI: 10.1103/PhysRevA.87.013847

Radially and azimuthally polarized nonparaxial Bessel beams made simple

Marco Ornigotti, Andrea Aiello

We present a method for the realization of radially and azimuthally polarized nonparaxial Bessel beams in a rigorous but simple manner. This result is achieved by using the concept of Hertz vector potential to generate exact vector solutions of Maxwell's equations from scalar Bessel beams. The scalar part of the Hertz potential is built by analogy with the paraxial case as a linear combination of Bessel beams carrying a unit of orbital angular momentum. In this way we are able to obtain spatial and polarization patterns analogous to the ones exhibited by the standard cylindrically polarized paraxial beams. Applications of these beams are discussed. (C) 2013 Optical Society of America

The phase shift induced by a single atom in free space

M. Sondermann, G. Leuchs

In this article we theoretically study the phase shift a single atom imprints onto a coherent state light beam in free space. The calculations are performed in a semiclassical framework. The key parameters governing the interaction and thus the measurable phase shift are the solid angle from which the light is focused onto the atom and the overlap of the incident radiation with the atomic dipole radiation pattern. The analysis includes saturation effects and discusses the associated Kerr-type non-linearity of a single atom.

Mid-infrared supercontinuum generation in As2S3-silica "nano-spike" step-index waveguide

N. Granzow, M. A. Schmidt, W. Chang, L. Wang, Q. Coulombier, J. Troles, P. Toupin, I. Hartl, K. F. Lee, et al.

Efficient generation of a broad-band mid-infrared supercontinuum spectrum is reported in an arsenic trisulphide waveguide embedded in silica. A chalcogenide "nano-spike", designed to transform the incident light adiabatically into the fundamental mode of a 2-mm-long uniform section 1 mu m in diameter, is used to achieve high launch efficiencies. The nano-spike is fully encapsulated in a fused silica cladding, protecting it from the environment. Nano-spikes provide a convenient means of launching light into sub-wavelength scale waveguides. Ultrashort (65 fs, repetition rate 100 MHz) pulses at wavelength 2 mu m, delivered from a Tm-doped fiber laser, are launched with an efficiency similar to 12% into the sub-wavelength chalcogenide waveguide. Soliton fission and dispersive wave generation along the uniform section result in spectral broadening out to almost 4 mu m for launched energies of only 18 pJ. The spectrum generated will have immediate uses in metrology and infrared spectroscopy. (C) 2013 Optical Society of America

Level repulsion in hybrid photonic-plasmonic microresonators for enhanced biodetection

Matthew R. Foreman, Frank Vollmer

We theoretically analyze photonic-plasmonic coupling between a high-Q whispering gallery mode (WGM) resonator and a core-shell nanoparticle. Blue and red shifts of WGM resonances are shown to arise from crossing of the photonic and plasmonic modes. Level repulsion in the hybrid system is further seen to enable sensitivity enhancements in WGM sensors: maximal when the two resonators are detuned by half the plasmon linewidth. Approximate bounds are given to quantify possible enhancements. Criteria for reactive vs resistive coupling are also established.

Functional Plasmonic Nanocircuits with Low Insertion and Propagation Losses

Arian Kriesch, Stanley P. Burgos, Daniel Ploss, Hannes Pfeifer, Harry A. Atwater, Ulf Peschel

We experimentally demonstrate plasmonic nanocircuits operating as subdiffraction directional couplers optically excited with high efficiency from free-space using optical Yagi-Uda style antennas at lambda(0) = 1550 nm. The optical Yagi-Uda style antennas are designed to feed channel plasmon waveguides with high efficiency (45% in coupling, 60% total emission), narrow angular directivity (<40 degrees), and low insertion loss. SPP channel waveguides exhibit propagation lengths as large as 34 mu m with adiabatically tuned confinement and are integrated with ultracompact (5 x 10 mu m(2)), highly dispersive directional couplers, which enable 30 dB discrimination over Delta lambda = 200 nm with only 0.3 dB device loss.

Efficient optical pumping and high optical depth in a hollow-core photonic-crystal fibre for a broadband quantum memory

Michael R. Sprague, Duncan G. England, Amir Abdolvand, Joshua Nunn, Xian-Min Jin, W. Steven Kolthammer, Marco Barbieri, Bruno Rigal, Patrick S. Michelberger, et al.

The generation of large multiphoton quantum states-for applications in computing, metrology and simulation-requires a network of high-efficiency quantum memories capable of storing broadband pulses. Integrating these memories into a fibre offers a number of advantages towards realizing this goal: strong light-matter coupling at low powers, simplified alignment and compatibility with existing photonic architectures. Here, we introduce a large-core kagome-structured hollow-core fibre as a suitable platform for an integrated fibre-based quantum memory with a warm atomic vapour. We demonstrate, for the first time, efficient optical pumping in such a system, where 90 +/- 1% of atoms are prepared in the ground state. We measure high optical depths (3 x 10(4)) and narrow homogeneous linewidths (6 +/- 2 MHz) that do not exhibit significant transit-time broadening, showing that we can prepare a Lambda-level system in a pure state. Our results establish that kagome fibres are suitable for implementing a broadband, room-temperature quantum memory, as well as a range of nonlinear optical effects.

Measuring mechanical strain and twist using helical photonic crystal fiber

Xiaoming Xi, Gordon K. L. Wong, Thomas Weiss, Philip St J. Russell

Solid-core photonic crystal fiber (PCF) with a permanent helical twist exhibits dips in its transmission spectrum at certain wavelengths. These are associated with the formation of orbital angular momentum states in the cladding. Here we investigate the tuning of these states with mechanical torque and axial tension. The dip wavelengths are found to scale linearly with both axial strain and mechanical twist rate. Analysis shows that the tension-induced shift in resonance wavelength is determined both by the photoelastic effect and by the change in twist rate, while the torsion-induced wavelength shift depends only on the change in twist rate. Twisted PCF can act as an effective optically monitored torque-tension transducer, twist sensor, or strain gauge. (C) 2013 Optical Society of America

Graphene-clad tapered fiber: effective nonlinearity and propagation losses

A. V. Gorbach, A. Marini, D. V. Skryabin

We derive a pulse propagation equation for a graphene-clad optical fiber, treating the optical response of the graphene and nonlinearity of the dielectric fiber core as perturbations in asymptotic expansion of Maxwell equations. We analyze the effective nonlinear and attenuation coefficients due to the graphene layer. Based on the recent experimental measurements of the nonlinear graphene conductivity, we predict considerable enhancement of the effective nonlinearity for subwavelength fiber core diameters. (C) 2013 Optical Society of America

Goos-Hanchen and Imbert-Fedorov shifts for bounded wavepackets of light

Marco Ornigotti, Andrea Aiello

We present precise expressions for the spatial and angular Goos-Hanchen and Imbert-Fedorov shifts experienced by a longitudinally and transversally limited beam of light (wavepacket) upon reflection from a dielectric interface, as opposed to the well-known case of a monochromatic beam which is bounded in transverse directions but infinitely extended along the direction of propagation. This is done under the assumption that the detector time is longer than the temporal length of the wavepacket (wavepacket regime). Our results will be applied to the case of a Gaussian wavepacket and show that, at the leading order in the Taylor expansion of reflected field amplitudes, the results are the same as in the monochromatic case.

The effect of Landau-Zener dynamics on phonon lasing

Huaizhi Wu, Georg Heinrich, Florian Marquardt

Optomechanical systems couple light to the motion of nanomechanical objects. Intriguing new effects are observed in recent experiments that involve the dynamics of more than one optical mode. There, mechanical motion can stimulate strongly driven multi-mode photon dynamics that acts back on the mechanics via radiation forces. We show that even for two optical modes Landau-Zener-Stueckelberg oscillations of the light field drastically change the nonlinear attractor diagram of the resulting phonon lasing oscillations. Our findings illustrate the generic effects of Landau-Zener physics on back-action induced self-oscillations.

The Purcell factor of nanoresonators

Mario Agio, Diego Martin Cano

Advances in theoretical nano-optics provide new insights into how nanoscale modification of spontaneous emission can be realized.

Determination of the effective refractive index of nanoparticulate ITO layers

M. Baum, I. Alexeev, M. Latzel, S. H. Christiansen, M. Schmidt

Nanoparticles of transparent conducting oxides, such as indium tin oxide, can be used in printing techniques to generate functional layers for various optoelectronic devices. Since these deposition methods do not create fully consolidated films, the optical properties of such layers are expected to be notably different from those of the bulk material and should be characterized on their own. In this work we present a way to measure the effective refractive index of a particulate ITO layer by refraction of light. The obtained data points are used to identify an accurate layer model for spectroscopic ellipsometry. In this way the complex refractive index of the particle layer is determined in a wide spectral range from ultra violet to near infrared. (c) 2013 Optical Society of America

Material Properties of Laser-Welded Thin Silicon Foils

M. T. Hessmann, T. Kunz, M. Voigt, K. Cvecek, M. Schmidt, A. Bochmann, S. Christiansen, R. Auer, C. J. Brabec

An extended monocrystalline silicon base foil offers a great opportunity to combine low-cost production with high efficiency silicon solar cells on a large scale. By overcoming the area restriction of ingot-based monocrystalline silicon wafer production, costs could be decreased to thin film solar cell range. The extended monocrystalline silicon base foil consists of several individual thin silicon wafers which are welded together. A comparison of three different approaches to weld 50 mu m thin silicon foils is investigated here: (1) laser spot welding with low constant feed speed, (2) laser line welding, and (3) keyhole welding. Cross-sections are prepared and analyzed by electron backscatter diffraction (EBSD) to reveal changes in the crystal structure at the welding side after laser irradiation. The treatment leads to the appearance of new grains and boundaries. The induced internal stress, using the three different laser welding processes, was investigated by micro-Raman analysis. We conclude that the keyhole welding process is the most favorable to produce thin silicon foils.

Measuring three-dimensional interaction potentials using optical interference

Nassir Mojarad, Vahid Sandoghdar, Madhavi Krishnan

We describe the application of three-dimensional (3D) scattering interferometric (iSCAT) imaging to the measurement of spatial interaction potentials for nano-objects in solution. We study electrostatically trapped gold particles in a nanofluidic device and present details on axial particle localization in the presence of a strongly reflecting interface. Our results demonstrate high-speed (similar to kHz) particle tracking with subnanometer localization precision in the axial and average 2.5 nm in the lateral dimension. A comparison of the measured levitation heights of trapped particles with the calculated values for traps of various geometries reveals good agreement. Our work demonstrates that iSCAT imaging delivers label-free, high-speed and accurate 3D tracking of nano-objects conducive to probing weak and long-range interaction potentials in solution. (C) 2013 Optical Society of America

Goos-Hanchen and Imbert-Fedorov beam shifts: an overview

K. Y. Bliokh, A. Aiello

We consider reflection and transmission of polarized paraxial light beams at a plane dielectric interface. The field transformations taking into account a finite beam width are described based on the plane-wave representation and geometric rotations. Using geometrical-optics coordinate frames accompanying the beams, we construct an effective Jones matrix characterizing spatial-dispersion properties of the interface. This results in a unified self-consistent description of the Goos-Hanchen and Imbert-Fedorov shifts (the latter being also known as the spin Hall effect of light). Our description reveals the intimate relation of the transverse Imbert-Fedorov shift to the geometric phases between constituent waves in the beam spectrum and to the angular momentum conservation for the whole beam. Both spatial and angular shifts are considered as well as their analogues for higher-order vortex beams carrying intrinsic orbital angular momentum. We also give a brief overview of various extensions and generalizations of the basic beam-shift phenomena and related effects.

Whispering gallery modes at the rim of an axisymmetric optical resonator: Analytical versus numerical description and comparison with experiment

I. Breunig, B. Sturman, F. Sedlmeir, H. G. L. Schwefel, K. Buse

Optical whispering gallery modes (WGMs) of mm-sized axisymmetric resonators are well localized at the equator. Employing this distinctive feature, we obtain simple analytical relations for the frequencies and eigenfunctions of WGMs which include the major radius of the resonator and the curvature radius of the rim. Being compared with results of finite-element simulations, these relations show a high accuracy and practicability. High-precision free-spectral-range measurements with a millimeter-sized disc resonator made of MgF2 allow us to identify the WGMs and confirm the applicability of our analytical description. (C) 2013 Optical Society of America

Low loss hollow optical-waveguide connection from atmospheric pressure to ultra-high vacuum

A. Ermolov, K. F. Mak, F. Tani, P. Hoelzer, J. C. Travers, P. St J. Russell

A technique for optically accessing ultra-high vacuum environments, via a photonic-crystal fiber with a long small hollow core, is described. The small core and the long bore enable a pressure ratio of over 10(8) to be maintained between two environments, while permitting efficient and unimpeded delivery of light, including ultrashort optical pulses. This delivery can be either passive or can encompass nonlinear optical processes such as optical pulse compression, deep UV generation, supercontinuum generation, or other useful phenomena. (C) 2013 AIP Publishing LLC.

Strain history dependence of the nonlinear stress response of fibrin and collagen networks

Stefan Muenster, Louise M. Jawerth, Beverly A. Leslie, Jeffrey I. Weitz, Ben Fabry, David A. Weitz

We show that the nonlinear mechanical response of networks formed from un-cross-linked fibrin or collagen type I continually changes in response to repeated large-strain loading. We demonstrate that this dynamic evolution of the mechanical response arises from a shift of a characteristic nonlinear stress-strain relationship to higher strains. Therefore, the imposed loading does not weaken the underlying matrices but instead delays the occurrence of the strain stiffening. Using confocal microscopy, we present direct evidence that this behavior results from persistent lengthening of individual fibers caused by an interplay between fiber stretching and fiber buckling when the networks are repeatedly strained. Moreover, we show that covalent cross-linking of fibrin or collagen inhibits the shift of the nonlinear material response, suggesting that the molecular origin of individual fiber lengthening may be slip of monomers within the fibers. Thus, a fibrous architecture in combination with constituents that exhibit internal plasticity creates a material whose mechanical response adapts to external loading conditions. This design principle may be useful to engineer novel materials with this capability.

Formation of quartic solitons and a localized continuum in silicon-based slot waveguides

Samudra Roy, Fabio Biancalana

We explore the possibility of exciting the so-called quartic solitons in specially designed slot waveguides based on silicon and silica or silicon nanocrystals. This requires the excitation of the structure with quasi-transverse-magnetic polarized pulses-for which the Raman effect is absent-and at a specific infrared wavelength for which only the second- and fourth-order group velocity coefficients are nonvanishing. Pulses launched in these conditions will generate a spectrally localized continuum coming from the spectral interference of many quartic solitons. DOI: 10.1103/PhysRevA.87.025801

Beating the One-Half Limit of Ancilla-Free Linear Optics Bell Measurements

Hussain A. Zaidi, Peter van Loock

We show that optically encoded two-qubit Bell states can be unambiguously discriminated with a success probability of more than 50% in both single-rail and dual-rail encodings by using active linear-optical resources that include Gaussian squeezing operations. These results are in contrast to the well-known upper bound of 50% for unambiguous discrimination of dual-rail Bell states using passive, static linear optics and arbitrarily many vacuum modes. We present experimentally feasible schemes that improve the success probability to 64.3% in dual-rail and to 62.5% in single-rail for a uniform random distribution of Bell states. Conceptually, this demonstrates that neither interactions that induce nonlinear mode transformations (such as Kerr interactions) nor auxiliary entangled photons are required to go beyond the one-half limit. We discuss the optimality of our single-rail scheme and talk about an application of our dual-rail scheme in quantum communication.

Interferometric homogeneity test using adaptive frequency comb illumination

Klaus Mantel, Johannes Schwider

The homogeneity test of glass plates in a Fizeau interferometer requires the measurement of the glass sample in reflected as well as in transmitted light. For the measurement in transmitted light, the sample has to be inserted into the ray path of a Fizeau or Twyman-Green interferometer, which leads to a nested cavity setup. To separate the interference signals from the different cavities, we illuminate a Fizeau interferometer with an adaptive frequency comb. In this way, rigid glass plates can be measured, and linear variations in the homogeneity can also be detected. The adaptive frequency comb is provided by a variable Fabry-Perot filter under broadband illumination from a superluminescence diode. Compared to approaches using a two-beam interferometer as a filter for the broadband light source, the visibility of the fringe system is considerably higher. (C) 2013 Optical Society of America

Terahertz relativistic spatial solitons in doped graphene metamaterials

H. Dong, C. Conti, A. Marini, F. Biancalana

We propose an electrically tunable graphene-based metamaterial that shows a large nonlinear optical response at THz frequencies. The responsible nonlinearity comes from the intraband current, which we are able to calculate analytically. We demonstrate that the proposed metamaterial supports stable 2D spatial solitary waves. Our theoretical approach is not restricted to graphene, but can be applied to all materials exhibiting a conical dispersion supporting massless Dirac fermions.

Visualizing Multiphase Flow and Trapped Fluid Configurations in a Model Three-Dimensional Porous Medium

Amber T. Krummel, Sujit S. Datta, Stefan Muenster, David A. Weitz

We report an approach to fully visualize the flow of two immiscible fluids through a model three-dimensional (3-D) porous medium at pore-scale resolution. Using confocal microscopy, we directly image the drainage of the medium by the nonwetting oil and subsequent imbibition by the wetting fluid. During imbibition, the wetting fluid pinches off threads of oil in the narrow crevices of the medium, forming disconnected oil ganglia. Some of these ganglia remain trapped within the medium. By resolving the full 3-D structure of the trapped ganglia, we show that the typical ganglion size, as well as the total amount of residual oil, decreases as the capillary number Ca increases; this behavior reflects the competition between the viscous pressure in the wetting fluid and the capillary pressure required to force oil through the pores of the medium. This work thus shows how pore-scale fluid dynamics influence the trapped fluid configurations in multiphase flow through 3-D porous media. (C) 2013 American Institute of Chemical Engineers AIChE J, 59: 1022-1029, 2013

Spectrofluorimetry with attomole sensitivity in photonic crystal fibres

Gareth O. S. Williams, Tijmen G. Euser, Philip St J. Russell, Anita C. Jones

We report the use of photonic crystal fibres (PCF) as spectrofluorimetric systems in which sample solutions are excited within the microstructure of the fibre. The use of intra-fibre excitation has several advantages that combine to enable highly sensitive measurements of fluorescence spectra and lifetimes: long path-lengths are achieved by the efficient guidance of the fundamental mode; sample volumes contained within the micron-scale structure are very small, only a few nanolitres per cm of path; collection and guidance of the emitted fluorescence is efficient and the fluorescence lifetime is unperturbed. Fluorophores in bulk solution can be studied in hollow core PCF, whereas the use of PCF with a suspended, solid core enables selective excitation of molecules in close proximity to the silica surface, through interaction with the evanescent field. We demonstrate the measurement of fluorescence spectra and fluorescence lifetimes in each of these excitation regimes and report the detection of attomole quantities of fluorescein.

Chemical and (Photo)-Catalytical Transformations in Photonic Crystal Fibers

Matthias Schmidt, Ana M. Cubillas, Nicola Taccardi, Tijmen G. Euser, Till Cremer, Florian Maier, Hans-Peter Steinrueck, Philip St. J. Russell, Peter Wasserscheid, et al.

The concept of employing photonic crystal fibers for chemical and (photo)-catalytical transformations is presented. These optofluidic microdevices represent a versatile platform where light and fluids can interact for spectroscopic or photoactivation purposes. The use of photonic crystal fibers in chemistry and sensing is reviewed and recent applications as catalytic microreactors are presented. Results on homogeneous catalysis and the immobilization of homogeneous and heterogeneous catalysts in the fiber channels are discussed. The examples demonstrate that combining catalysis and the excellent light guidance of photonic crystal fibers provides unique features for example, for photocatalytic activation and quantitative photospectroscopic reaction analysis.

Identical classical particles: Half fermions and half bosons

Falk Toeppel, Andrea Aiello

We study the problem of particle indistinguishability for the three cases known in nature: identical classical particles, identical bosons, and identical fermions. By exploiting the fact that different types of particles are associated with Hilbert space vectors with different symmetries, we establish some relations between the expectation value of several different operators, as the particle number one and the interparticle correlation one, evaluated for states of a pair of identical classical particles, bosons, and fermions. We find that the quantum behavior of a pair of identical classical particles has exactly half fermionic and half bosonic characteristics.

Multiphoton nonclassical correlations in entangled squeezed vacuum states

Bhaskar Kanseri, Timur Iskhakov, Georgy Rytikov, Maria Chekhova, Gerd Leuchs

Photon-number correlation measurements are performed on bright squeezed vacuum states using a standard Bell-test setup, and quantum correlations are observed for conjugate polarization-frequency modes. We further test the entanglement witnesses for these states and demonstrate the violation of the separability criteria, which infers that all of the macroscopic Bell states, containing typically 10(6) photons per pulse, are polarization entangled. The study also reveals the symmetry of macroscopic Bell states with respect to local polarization transformations. DOI: 10.1103/PhysRevA.87.032110

Vector modulational instability induced by parametric resonance in periodically tapered highly birefringent optical fibers

Andrea Armaroli, Fabio Biancalana

We study the modulational instability induced by periodic variations of group-velocity dispersion and nonlinear coefficients in a highly birefringent fiber. We observe, for each resonance order, the presence of two pairs of genuine vector-type sidebands, which are spectrally unbalanced between the polarization components for nonzero group-index mismatch, and one pair of balanced sidebands emerging and dominating at increasing group-index mismatch. As the conventional modulational instabilitymanifests itself, it is partially suppressed by the proximity of these additional unstable regions.

Interference of conically scattered light in surface plasmon resonance

Aaron Webster, Frank Vollmer

Surface plasmon polaritons on thin metal films are a well studied phenomena when excited using prism coupled geometries such as the Kretschmann attenuated total reflection configuration. Here we describe a novel interference pattern in the conically scattered light emanating from such a configuration when illuminated by a focused beam. We observe conditions indicating only self-interference of scattered surface plasmon polaritions without any contributions from specular reflection. The spatial evolution of this field is described in the context of Fourier optics and has applications in highly sensitive surface plasmon based biosensing. (C) 2013 Optical Society of America

Self-frequency blueshift of dissipative solitons in silicon-based waveguides

Samudra Roy, Andrea Marini, Fabio Biancalana

We analyze the dynamics of dissipative solitons in silicon on insulatorwaveguides embedded in a gain medium. The optical propagation is modeled through a cubicGinzburg-Landau equation for the field envelope coupled with an ordinary differential equation accounting for the generation of free carriers owing to two-photon absorption. Our numerical simulations clearly indicate that dissipative solitons accelerate due to the carrier-induced index change and experience a considerable blueshift, which is mainly hampered by the gain dispersion of the active material. Numerical results are fully explained by analytical predictions based on soliton perturbation theory.

Five-ring hollow-core photonic crystal fiber with 1.8 dB/km loss

M. H. Frosz, J. Nold, T. Weiss, A. Stefani, F. Babic, S. Rammler, P. St. J. Russell

A 19-cell hollow-core photonic crystal fiber reaching 1.8 +/- 0.5 dB/km loss at 1530 nm is reported. Despite expanded corner holes in the first ring adjacent to the core, and only five cladding rings, the minimum loss is close to the previously published record of 1.7 dB/km at a comparable wavelength, achieved in a fiber with seven cladding rings. Since each additional cladding ring requires a significant increase in fabrication time and complexity, it is highly desirable to use as few as possible while still achieving low loss. Modeling results confirm that further reducing cladding deformations would yield only a small decrease in loss. This demonstrates that loss comparable to the previously demonstrated lowest-loss bandgap fibers can be achieved with fiber structures that are significantly simpler and faster to fabricate. (C) 2013 Optical Society of America

Combined soliton pulse compression and plasma-related frequency upconversion in gas-filled photonic crystal fiber

W. Chang, P. Hoelzer, J. C. Travers, P. St. J. Russell

We numerically investigate self-frequency blueshifting of a fundamental soliton in a gas-filled hollow-core photonic crystal fiber. Because of the changing underlying soliton parameters, the blueshift gives rise to adiabatic soliton compression. Based on these features, we propose a device that enables frequency shifting over an octave and pulse compression from 30 fs down to 2.3 fs. (C) 2013 Optical Society of America

Theory of resonance shifts of whispering gallery modes by arbitrary plasmonic nanoparticles

Matthew R. Foreman, Frank Vollmer

Shifts of the resonance frequency of high Q whispering gallery modes (WGMs) in spherical dielectric microresonators by plasmonic nanoparticles can be greater than the WGM line width, such that the perturbation theory commonly used for describing resonance shifts by dielectric nanoparticles (Teraoka and Arnold 2006 J. Opt. Soc. Am. B 23 1381) is no longer applicable. This paper therefore reports on an analytic framework, based on generalized Lorenz-Mie theory, capable of describing resonance shifts by metallic nanoparticles supporting plasmon oscillations. Generalization to nanoparticles of arbitrary geometry is presented by employing the extended boundary condition method. Within this framework, hybrid resonance conditions for coupled spherical photonic and plasmonic resonators are established and shown to simplify for small plasmonic nanoparticles. Approximate analytic formulae are derived for the shift and broadening of the isolated WGM and plasmon resonances, from which either apparent resonance shifts or mode splitting are shown to follow. Tuning of plasmon resonances using, for example, core-shell nanoparticles to attain a large spectral overlap between WGM and plasmon resonances is demonstrated to significantly enhance the magnitude of resonance shifts, with a 60-fold enhancement achieved without any optimization. Hybridization of photonic-plasmonic resonances is furthermore demonstrated (in addition to hybridization of transverse electric-transverse magnetic WGMs) and the associated level repulsion illustrated. Finally, the dependence of WGM resonance shifts on the orientation of silver nanorods is theoretically investigated and found to be strong by virtue of the asymmetry of the nanorod.

Squeezed light from a silicon micromechanical resonator

Amir H. Safavi-Naeini, Simon Groeblacher, Jeff T. Hill, Jasper Chan, Markus Aspelmeyer, Oskar Painter

Monitoring a mechanical object's motion, even with the gentle touch of light, fundamentally alters its dynamics. The experimental manifestation of this basic principle of quantum mechanics, its link to the quantum nature of light and the extension of quantum measurement to the macroscopic realm have all received extensive attention over the past half-century(1,2). The use of squeezed light, with quantum fluctuations below that of the vacuum field, was proposed nearly three decades ago(3) as a means of reducing the optical read-out noise in precision force measurements. Conversely, it has also been proposed that a continuous measurement of a mirror's position with light may itself give rise to squeezed light(4,5). Such squeezed-light generation has recently been demonstrated in a system of ultracold gas-phase atoms(6) whose centre-of-mass motion is analogous to the motion of a mirror. Here we describe the continuous position measurement of a solid-state, optomechanical system fabricated from a silicon microchip and comprising a micromechanical resonator coupled to a nanophotonic cavity. Laser light sent into the cavity is used to measure the fluctuations in the position of the mechanical resonator at a measurement rate comparable to its resonance frequency and greater than its thermal decoherence rate. Despite the mechanical resonator's highly excited thermal state (10(4) phonons), we observe, through homodyne detection, squeezing of the reflected light's fluctuation spectrum at a level 4.5 +/- 0.2 per cent below that of vacuum noise over a bandwidth of a few megahertz around the mechanical resonance frequency of 28 megahertz. With further device improvements, on-chip squeezing at significant levels should be possible, making such integrated microscale devices well suited for precision metrology applications.

High quality factor whispering gallery modes from self-assembled hexagonal GaN rods grown by metal-organic vapor phase epitaxy

C. Tessarek, G. Sarau, M. Kiometzis, S. Christiansen

Self-assembled GaN rods were grown on sapphire by metalorganic vapor phase epitaxy using a simple two-step method that relies first on a nitridation step followed by GaN epitaxy. The mask-free rods formed without any additional catalyst. Most of the vertically aligned rods exhibit a regular hexagonal shape with sharp edges and smooth sidewall facets. Cathodo-and microphotoluminescence investigations were carried out on single GaN rods. Whispering gallery modes with quality factors greater than 4000 were measured demonstrating the high morphological and optical quality of the self-assembled GaN rods. (C) 2012 Optical Society of America

Stokes vector based polarization resolved second harmonic microscopy of starch granules

Nirmal Mazumder, Jianjun Qiu, Matthew R. Foreman, Carlos Macias Romero, Peter Toeroek, Fu-Jen Kao

We report on the measurement and analysis of the polarization state of second harmonic signals generated by starch granules, using a four-channel photon counting based Stokes-polarimeter. Various polarization parameters, such as the degree of polarization (DOP), the degree of linear polarization (DOLP), the degree of circular polarization (DOCP), and anisotropy are extracted from the 2D second harmonic Stokes images of starch granules. The concentric shell structure of a starch granule forms a natural photonic crystal structure. By integration over all the solid angle, it will allow very similar SHG quantum efficiency regardless of the angle or the states of incident polarization. Given type I phase matching and the concentric shell structure of a starch granule, one can easily infer the polarization states of the input beam from the resulting SH micrograph. (C) 2013 Optical Society of America

Arrayed free space continuous-wave terahertz photomixers

S. T. Bauerschmidt, G. H. Doehler, H. Lu, A. C. Gossard, S. Malzer, S. Preu

We present free space coherent arrays of continuous-wave terahertz (THz) photomixers and compare the results to on-chip arrays. By altering the relative phases of the exciting laser signals, the relative THz phase between the array elements can be tuned, allowing for beam steering. In addition, the constructive interference of the emission of N elements leads to an increase of the focal intensity by a factor of N-2 while reducing the beam width by similar to N-1, below the diffraction limit of a single source. Such array architectures strongly improve the THz power distribution for stand-off spectroscopy and imaging systems while providing a huge bandwidth at the same time. We demonstrate this by beam profiles generated by a 2 x 2 and a 4 x 1 array for a transmission distance of 4.2 m. Spectra between 70 GHz and 1.1 THz have been recorded with these arrays. (C) 2013 Optical Society of America

Geometrical aspects of PT-invariant transfer matrices

J. J. Monzon, A. G. Barriuso, J. M. Montesinos-Amilibia, L. L. Sanchez-Soto

We show that the transfer matrix for a PT-invariant system, when recast in the appropriate variables, can be interpreted as a point in the (3 + 1)-dimensional de Sitter space. We introduce a natural PT-invariant composition law for these matrices and confirm that their action appears as a Lorentz transformation. We elucidate the geometrical meaning of the PT symmetry breaking and suggest that the cosmological event horizon arising in the de Sitter metric can be can be unraveled with a simple optical scheme. DOI: 10.1103/PhysRevA.87.012111

Ultrashort Self-Induced Transparency Plasmon Solitons

Andrea Marini, Fabio Biancalana

We study the interband self-induced transmission of surface plasmon polaritons in a gold film surrounded by an external Kerr medium. We model the optical propagation by using a version of the generalized nonlinear Schrodinger equation for the field envelope coupled to Bloch equations for valence electrons of gold, predicting self-induced transparency of ultrashort plasmon solitons with a pulse duration below 10 fs. We demonstrate that the Kerr nonlinearity from the surrounding dielectric can be used to compensate for the group velocity dispersion, and that the impact of dephasing and decay processes can be effectively reduced by the self-induced transmission mechanism.

Experimental characterization of an uniaxial angle cut whispering gallery mode resonator

Florian Sedlmeir, Martin Hauer, Josef U. Fuerst, Gerd Leuchs, Harald G. L. Schwefel

The usual configuration of uniaxial whispering gallery mode resonators is a disk shaped geometry where the optic axis points along the symmetry axis, a so called z-cut resonator. Recently x-cut resonators, where the optic axis lies in the equatorial plane, became of interest as they enable extremely broadband second harmonic generation. In this paper we report on the properties of a more generalized system, the so called angle-cut resonator, where the optic axis exhibits an arbitrary angle against the symmetry axis. We show experimentally that the modal structure and quality factors are similar to common resonators but that the polarization properties differ quite significantly: due to the asymmetry the polarization depends on the equatorial position and is, in general, elliptical. (C) 2013 Optical Society of America

The Schmidt modes of biphoton qutrits: Poincare-sphere representation

M. V. Chekhova, M. V. Fedorov

For a general-form polarization biphoton qutrit, physically corresponding to a pair of arbitrarily polarized photons in a single frequency and wavevector mode, we explicitly find polarization Schmidt modes. A simple method is suggested for factorizing the state vector and the explicit expressions for the factorizing photon creation operators are found. The degrees of entanglement and polarization of a qutrit are shown to depend directly on the commutation features of the factorizing operators. Clear graphic representations for the Stokes vectors of the qutrit state as a whole, its Schmidt modes and factorizing single-photon creation operators are given based on the Poincare sphere. An experimental scheme is proposed for measuring the parameters of the Schmidt decomposition as well as for demonstrating the operational meaning of qutrit entanglement.

Optomechanically Induced Transparency in the Nonlinear Quantum Regime

Andreas Kronwald, Florian Marquardt

Optomechanical systems have been shown both theoretically and experimentally to exhibit an analogon to atomic electromagnetically induced transparency, with sharp transmission features that are controlled by a second laser beam. Here we investigate these effects in the regime where the fundamental nonlinear nature of the optomechanical interaction becomes important. We demonstrate that pulsed transistorlike switching of transmission still works even in this regime. We also show that optomechanically induced transparency at the second mechanical sideband could be a sensitive tool to see first indications of the nonlinear quantum nature of the optomechanical interaction even for single-photon coupling strengths significantly smaller than the cavity linewidth.

Nonparaxial accelerating Bessel-like beams

Ioannis D. Chremmos, Nikolaos K. Efremidis

A class of nonparaxial accelerating optical waves is introduced. These are beams with a Bessel-like profile that are capable of shifting laterally along fairly arbitrary trajectories as the wave propagates in free space. The concept expands on our previous proposal of paraxial accelerating Bessel-like beams to include beams with subwavelength lobes and/or large trajectory angles. Such waves are produced when the phase at the input plane is engineered so that the interfering ray cones are made to focus along the prespecified path. When the angle of these cones is fixed, the beams possess a diffraction-free Bessel profile on planes that stay normal to their trajectory, which can be considered as a generalized definition of diffractionless propagation in the nonparaxial regime. The analytical procedure leading to these results is based on a ray-optics interpretation of Rayleigh-Sommerfeld diffraction and is presented in detail. The evolution of the proposed waves is demonstrated through a series of numerical examples and a variety of trajectories.

Arbitrarily large steady-state bosonic squeezing via dissipation

Andreas Kronwald, Florian Marquardt, Aashish A. Clerk

We discuss how large amounts of steady-state quantum squeezing (beyond 3 dB) of a mechanical resonator can be obtained by driving an optomechanical cavity with two control lasers with differing amplitudes. The scheme does not rely on any explicit measurement or feedback, nor does it simply involve a modulation of an optical spring constant. Instead, it uses a dissipative mechanism with the driven cavity acting as an engineered reservoir. It can equivalently be viewed as a coherent feedback process, obtained by minimally perturbing the quantum nondemolition measurement of a single mechanical quadrature. This shows that in general the concepts of coherent feedback schemes and reservoir engineering are closely related. We analyze how to optimize the scheme, how the squeezing scales with system parameters, and how it may be directly detected from the cavity output. Our scheme is extremely general, and could also be implemented with, e.g., superconducting circuits.

Ultrafast coherent nanoscopy

Xue-Wen Chen, Ahmad Mohammadi, Amir Hossein Baradaran Ghasemi, Mario Agio

The dramatic advances of nanotechnology experienced in recent years enabled us to fabricate optical nanostructures or nano-antennas that greatly enhance the conversion of localised electromagnetic energy into radiation and vice versa. Nano-antennas offer the required improvements in terms of bandwidth, interaction strength and resolution for combining ultrafast spectroscopy, nano-optics and quantum optics to fundamentally push forward the possibility of the coherent optical access on individual nanostructures or even molecules above cryogenic temperatures, where dephasing processes typically occur at very short time scales. In this context, we discuss recent progress in the theoretical description of light-matter interaction at the nanoscale and related experimental findings. Moreover, we present concrete examples in support of our vision and propose a series of experiments that aim at exploring novel promising regimes of optical coherence and quantum optics in advanced spectroscopy. We envisage extensions to ultrafast and nonlinear phenomena, especially in the direction of multidimensional nanoscopy.

Goos-Hanchen and Imbert-Fedorov shifts from a quantum-mechanical perspective

Falk Toeppel, Marco Ornigotti, Andrea Aiello

We study the classical optics effects known as Goos-Hanchen and Imbert-Fedorov shifts, occurring when reflecting a bounded light beam from a planar surface, by using a quantum-mechanical formalism. This new approach allows us to naturally separate the spatial shift into two parts, one independent on orbital angular momentum (OAM) and the other one showing OAM-induced spatial-versus-angular shift mixing. In addition, within this quantum-mechanical-like formalism, it becomes apparent that the angular shift is proportional to the beams angular spread, namely to the variance of the transverse components of the wave vector. Moreover, we extend our treatment to the enhancement of beam shifts via weak measurements and relate our results to the recent experiments.

A sum rule for charged elementary particles

Gerd Leuchs, Luis L. Sanchez-Soto

There may be a link between the quantum properties of the vacuum and the parameters describing the properties of light propagation, culminating in a sum over all types of elementary particles existing in Nature weighted only by their squared charges and independent of their masses. The estimate for that sum is of the order of 100.

QED with a parabolic mirror

G. Alber, J. Z. Bernad, M. Stobinska, L. L. Sanchez-Soto, G. Leuchs

We investigate the quantum electrodynamics of a single two-level atom located at the focus of a parabolic cavity. We first work out the modifications of the spontaneous emission induced by the presence of this boundary in the optical regime, where the dipole and the rotating-wave approximations apply. Furthermore, the single-photon state that leaves the cavity asymptotically is determined. The corresponding time-reversed single-photon quantum state is capable of exciting the atom in this extreme multimode scenario with near-unit probability. Using semiclassical methods, we derive a photon-path representation for the relevant transition amplitudes and show that it constitutes a satisfactory approximation for a wide range of wavelengths.

A versatile source of single photons for quantum information processing

Michael Foertsch, Josef U. Fuerst, Christoffer Wittmann, Dmitry Strekalov, Andrea Aiello, Maria V. Chekhova, Christine Silberhorn, Gerd Leuchs, Christoph Marquardt

The generation of high-quality single-photon states with controllable narrow spectral bandwidths and central frequencies is key to facilitate efficient coupling of any atomic system to non-classical light fields. Such an interaction is essential in numerous experiments for fundamental science and applications in quantum communication and information processing, as well as in quantum metrology. Here we implement a fully tunable, narrow-band and efficient single-photon source based on a whispering gallery mode resonator. Our disk-shaped, monolithic and intrinsically stable resonator is made of lithium niobate and supports a cavity-assisted spontaneous parametric down-conversion process. The generated photon pairs are emitted into two highly tunable resonator modes. We verify wavelength tuning over 100 nm of both modes with controllable bandwidth between 7.2 and 13 MHz. Heralding of single photons yields anti-bunching with g((2))(0) < 0.2.

Polarization assisted fast data encoding and transmission using coherence based spectral anomalies

Bhaskar Kanseri

Two methods for fast information encoding and free space communication are proposed, which are based on the rapid transitions in coherence-based (spatial and temporal) spectral anomalies called 'spectral switches'. The information (data bits) could be encoded in terms of red and blue shifts in the source spectrum. The encoding process itself could be made fast by polarization assisted switching of spectral anomalies using a polarization selective device such as an electro-optic modulator. The advantages and limitations of this polarization based data processing mechanism are also discussed.

Growth of GaN Nanorods and Wires and Spectral Tuning of Whispering Gallery Modes in Tapered GaN Wires

Christian Tessarek, Christel Dieker, Erdmann Spiecker, Silke Christiansen

This paper reports on the growth of GaN nanorods and wires by metal-organic vapor phase epitaxy. Density, height and diameter are strongly influenced by the growth time. A deposition time of a few minutes leads to the formation of GaN nanorods. Increasing the deposition time up to 1 h yields wires with heights exceeding 47 mu m. Transmission electron microscopy and convergent beam electron diffraction measurements are showing the presence of N- and Ga-polar GaN in a single nanorod. Cathodoluminescence measurements are performed showing the appearance of whispering gallery modes. Due to slight tapering of the wires the whispering gallery modes can be spectrally tuned by changing the position of the exposing electron beam at the sidewall facet of the rod. (C) 2013 The Japan Society of Applied Physics

Topological Zeeman effect and circular birefringence in twisted photonic crystal fibers

T. Weiss, G. K. L. Wong, F. Biancalana, S. M. Barnett, X. M. Xi, P. St. J. Russell

The propagation of light guided in optical fibers is affected in different ways by bending or twisting. Here we treat the polarization properties of twisted six-fold symmetric photonic crystal fibers. Using a coordinate frame that follows the twisting structure, we show that the governing equation for the fiber modes resembles the Pauli equation for electrons in weak magnetic fields. This implies index splitting between left and right circularly polarized modes, which are degenerate in the untwisted fiber. We develop a theoretical model, based on perturbation theory and symmetry properties, to predict the observable circular birefringence (i.e., optical activity) associated with this splitting. Our overall conclusion is that optical activity requires the rotational symmetry to be broken so as to allow coupling between different total angular momentum states. (C) 2013 Optical Society of America

Local Softening of Information Geometric Indicators of Chaos in Statistical Modeling in the Presence of Quantum-Like Considerations

Adom Giffin, Sean A. Ali, Carlo Cafaro

In a previous paper (C. Cafaro et al., 2012), we compared an uncorrelated 3 D Gaussian statistical model to an uncorrelated 2 D Gaussian statistical model obtained from the former model by introducing a constraint that resembles the quantum mechanical canonical minimum uncertainty relation. Analysis was completed by way of the information geometry and the entropic dynamics of each system. This analysis revealed that the chaoticity of the 2 D Gaussian statistical model, quantified by means of the Information Geometric Entropy (IGE), is softened or weakened with respect to the chaoticity of the 3 D Gaussian statistical model, due to the accessibility of more information. In this companion work, we further constrain the system in the context of a correlation constraint among the system's micro-variables and show that the chaoticity is further weakened, but only locally. Finally, the physicality of the constraints is briefly discussed, particularly in the context of quantum entanglement.

Performance of scientific cameras with different sensor types in measuring dynamic processes in fluorescence microscopy

Jasmin Jung, Siegfried Weisenburger, Sahradha Albert, Daniel F. Gilbert, Oliver Friedrich, Volker Eulenburg, Johannes Kornhuber, Teja W. Groemer

The plethora of available scientific cameras of different types challenges the biologically oriented experimenter when picking the appropriate camera for his experiment. In this study, we chose to investigate camera performances in a typical nonsingle molecule situation in life sciences, that is, quantitative measurements of fluorescence intensity changes from video data with typically skewed intensity distributions. Here, intensity profile dynamics of pH-sensors upon triggered changes of pH-environments in living cells served as a model system. The following camera types were tested: sCMOS, CCD (scientific and nonscientific) and EM-CCD (back-and front-illuminated). We found that although the EM-CCD cameras achieved the best absolute spatial SNR (signal-to-noise ratio) values, the sCMOS was at least of equal performance when the spatial SNR was related to the effective dynamic range, and it was superior in terms of temporal SNR. In the measurements of triggered intensity changes, the sCMOS camera had the advantage that it used the smallest fraction of its dynamic range when depicting intensity changes, and thus featured the best SNR at full usage of its dynamic range. (C) 2013 Wiley Periodicals, Inc.

A Simplified Implementation of the Bubble Analysis of Biopolymer Network Pores

Stefan Muenster, Ben Fabry

Amplification of realistic Schrodinger-cat-state-like states by homodyne heralding

Amine Laghaout, Jonas S. Neergaard-Nielsen, Ioannes Rigas, Christian Kragh, Anders Tipsmark, Ulrik L. Andersen

We present a scheme for the amplification of Schrodinger cat states that collapses two smaller states onto their constructive interference via a homodyne projection. We analyze the performance of the amplification in terms of fidelity and success rate when the input consists of either exact coherent state superpositions or of photon-subtracted squeezed vacua. The impact of imprecise homodyne detection and of impure squeezing is quantified. We also assess the scalability of iterated amplifications. DOI: 10.1103/PhysRevA.87.043826

A gold-nanotip optical fiber for plasmon-enhanced near-field detection

P. Uebel, S. T. Bauerschmidt, M. A. Schmidt, P. St. J. Russell

A wet-chemical etching and mechanical cleaving technique is used to fabricate gold nanotips attached to tapered optical fibers. Localized surface plasmon resonances (tunable from 500 to 850 nm by varying the tip dimensions) are excited at the tip, and the signal is transmitted via the fiber to an optical analyzer, making the device a plasmon-enhanced near-field probe. A simple cavity model is used to explain the resonances observed in numerical simulations. (C) 2013 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

Total internal reflection of orbital angular momentum beams

W. Loffler, N. Hermosa, Andrea Aiello, J. P. Woerdman

We investigate how beams with orbital angular momentum (OAM) behave under total internal reflection. This is studied in two complementary experiments: in the first experiment, we study geometric shifts of OAM beams upon total internal reflection (Goos-Hanchen and Imbert-Fedorov shifts, for each the spatial and angular variant), and in the second experiment we determine changes in the OAM mode spectrum of a beam, again upon total internal reflection. As a result we find that, in the first case, the shifts are independent of OAM and beam focusing, while in the second case, modifications in the OAM spectrum occur which depend on the input OAM mode as well as on the beam focusing. This is investigated by experiment and theory. We also show how the two methods, beam shifts on the one hand, and OAM spectrum changes on the other, are related theoretically.

Mimicking the nonlinear dynamics of optical fibers with waveguide arrays: towards a spatiotemporal supercontinuum generation

Truong X. Tran, Fabio Biancalana

We numerically demonstrate the formation of the spatiotemporal version of the so-called diffractive resonant radiation generated in waveguide arrays with Kerr nonlinearity when a long pulse is launched into the system. The phase matching condition for the diffractive resonant radiation that we have found earlier for CW beams also works well in the spatiotemporal case. By introducing a linear potential, one can introduce a continuous shift of the central wavenumber of a linear pulse, whereas in the nonlinear case one can demonstrate that the soliton self-wavenumber shift can be compensated by the emission of diffractive resonant radiation, in a very similar fashion as it is done in optical fibers. This work paves the way for designing unique optical devices that generate spectrally broad supercontinua with a controllable directionality by taking advantage of the combined physics of optical fibers and waveguide arrays. (C) 2013 Optical Society of America

Corrections to the knife-edge based reconstruction scheme of tightly focused light beams

C. Huber, S. Orlov, P. Banzer, G. Leuchs

The knife-edge method is an established technique for profiling light beams. It was shown, that this technique even works for tightly focused beams, if the material and geometry of the probing knife-edges are chosen carefully. Furthermore, it was also reported recently that this method fails, when the knife-edges are made from pure materials. The artifacts introduced in the reconstructed beam shape and position depend strongly on the edge and input beam parameters, because the knife-edge is excited by the incoming beam. Here we show, that the actual beam shape and spot size of tightly focused beams can still be derived from knife-edge measurements for pure edge materials and different edge thicknesses by adapting the analysis method of the experimental data taking into account the interaction of the beam with the edge. (C) 2013 Optical Society of America

Finite element simulation of a perturbed axial-symmetric whispering-gallery mode and its use for intensity enhancement with a nanoparticle coupled to a microtoroid

Alex Kaplan, Matthew Tomes, Tal Carmon, Maxim Kozlov, Oren Cohen, Guy Bartal, Harald G. L. Schwefel

We present an optical mode solver for a whispering gallery resonator coupled to an adjacent arbitrary shaped nano-particle that breaks the axial symmetry of the resonator. Such a hybrid resonator-nanoparticle is similar to what was recently used for bio-detection and for field enhancement. We demonstrate our solver by parametrically studying a toroid-nanoplasmonic device and get the optimal nano-plasmonic size for maximal enhancement. We investigate cases near a plasmonic resonance as well as far from a plasmonic resonance. Unlike common plasmons that typically benefit from working near their resonance, here working far from plasmonic resonance provides comparable performance. This is because the plasmonic resonance enhancement is accompanied by cavity quality degradation through plasmonic absorption. (C) 2013 Optical Society of America

Ultrafast nonlinear dynamics of surface plasmon polaritons in gold nanowires due to the intrinsic nonlinearity of metals

A. Marini, M. Conforti, G. Della Valle, H. W. Lee, Tr X. Tran, W. Chang, M. A. Schmidt, S. Longhi, P. St J. Russell, et al.

Starting from first principles, we theoretically model the nonlinear temporal dynamics of gold-based plasmonic devices resulting from the heating of their metallic components. At optical frequencies, the gold susceptibility is determined by the interband transitions around the X, L points in the first Brillouin zone, and thermo-modulational effects ensue from Fermi smearing of the electronic energy distribution in the conduction band. As a consequence of light-induced heating of the conduction electrons, the optical susceptibility becomes nonlinear. In this paper we describe, for the first time to our knowledge, the effects of the thermo-modulational nonlinearity of gold on the propagation of surface plasmon polaritons guided on gold nanowires. We introduce a novel nonlinear Schrodinger-like equation to describe pulse propagation in such nanowires, and we predict the appearance of an intense spectral red-shift caused by the delayed thermal response.

Enhanced Raman Scattering of Graphene using Arrays of Split Ring Resonators

George Sarau, Basudev Lahiri, Peter Banzer, Priti Gupta, Arnab Bhattacharya, Frank Vollmer, Silke Christiansen

Combining graphene with plasmonic nanostructures is currently being explored for high sensitivity biochemical detection based on the surface-enhanced Raman scattering (SERS) effect. Here, a novel and tunable platform for understanding SERS based on graphene monolayers transferred on arrays of split ring resonators (SRRs) exhibiting resonances in the visible range is introduced. Raman enhancement factors per area of graphene of up to 75 are measured, demonstrating the strong plasmonic coupling between graphene and the metamaterial resonances. Apart from the incident laser light, both the photoluminescence signal emitted by the SRRs and the Raman scattered light from graphene contribute to the excitation of distinct resonances, resulting in different SERS. This new perspective allows control of SERS in the case of graphene on plasmonic metamaterials or nanostructures and potentially paves the way towards an advanced SERS substrate that could lead to the detection of single molecules attached to graphene in future biochemical sensing devices.

Controlling morphology and optical properties of self-catalyzed, mask-free GaN rods and nanorods by metal-organic vapor phase epitaxy

C. Tessarek, M. Bashouti, M. Heilmann, C. Dieker, I. Knoke, E. Spiecker, S. Christiansen

A simple self-catalyzed and mask-free approach will be presented to grow GaN rods and nanorods based on the metal-organic vapor phase epitaxy technique. The growth parameter dependent adjustment of the morphology of the structures will be discussed. Rods and nanorods with diameters reaching from a few mu m down to 100 nm, heights up to 48 mu m, and densities up to 8.10(7) cm(-2) are all vertically aligned with respect to the sample surface and exhibiting a hexagonal shape with smooth sidewall facets. Optical properties of GaN nanorods were determined using cathodoluminescence. It will be shown that the optical properties can be improved just by reducing the Ga precursor flow. Furthermore, for regular hexagonal shaped rods and nanorods, whispering gallery modes with quality factors up to 500 were observed by cathodoluminescence pointing out high morphological quality of the structures. Structural investigations using transmission electron microscopy show that larger GaN nanorods (diameter > 500 nm) contain threading dislocations in the bottom part and vertical inversion domain boundaries, which separate a Ga-polar core from a N-polar shell. In contrast, small GaN nanorods (similar to 200 nm) are largely free of such extended defects. Finally, evidence for a self-catalyzed, Ga-induced vapor-liquid-solid growth will be discussed. (C) 2013 AIP Publishing LLC.

Efficient anti-Stokes generation via intermodal stimulated Raman scattering in gas-filled hollow-core PCF

B. M. Trabold, A. Abdolvand, T. G. Euser, P. St J. Russell

A strong anti-Stokes Raman signal, from the vibrational Q(1) transition of hydrogen, is generated in gas-filled hollow-core photonic crystal fiber. To be efficient, this process requires phase-matching, which is not automatically provided since the group velocity dispersion is typically non-zero and-inside a fiber-cannot be compensated for using a crossedbeam geometry. Phase-matching can however be arranged by exploiting the different dispersion profiles of higher-order modes. We demonstrate the generation of first and second anti-Stokes signals in higher-order modes by pumping with an appropriate mixture of fundamental and a higher-order modes, synthesized using a spatial light modulator. Conversion efficiencies as high as 5.3% are achieved from the pump to the first anti-Stokes band. (C) 2013 Optical Society of America

Optical diametric drive acceleration through action-reaction symmetry breaking

Martin Wimmer, Alois Regensburger, Christoph Bersch, Mohammad-Ali Miri, Sascha Batz, Georgy Onishchukov, Demetrios N. Christodoulides, Ulf Peschel

Newton's third law of motion is one of the pillars of classical physics. This fundamental principle states that the forces two bodies exert on each other are equal and opposite. Had the resulting accelerations been oriented in the same direction, this would have instead led to a counterintuitive phenomenon, that of diametric drive(1). In such a hypothetical arrangement, two interacting particles constantly accelerate each other in the same direction through a violation of the action-reaction symmetry. Although in classical mechanics any realization of this process requires one of the two particles to have a negative mass and hence is strictly forbidden, it could nevertheless be feasible in periodic structures where the effective mass can also attain a negative sign(2-7). Here we report the first experimental observation of such diametric drive acceleration for pulses propagating in a nonlinear optical mesh lattice(8-14). The demonstrated reversal of action-reaction symmetry could enable altogether new possibilities for frequency conversion and pulse-steering applications.

Structure and mechanics of fibrin clots formed under mechanical perturbation

S. Muenster, L. M. Jawerth, B. Fabry, D. A. Weitz

Interaction between optical fields and their conjugates in nonlinear media

Matteo Conforti, Andrea Marini, Truong X. Tran, Daniele Faccio, Fabio Biancalana

Motivated by recent experimental results, we demonstrate that the ubiquitous pulse propagation equation based on a single generalized nonlinear Schrodinger equation is incomplete and inadequate to explain the formation of the so called negative-frequency resonant radiation emitted by optical solitons. The origin of this deficiency is due to the absence of a peculiar nonlinear coupling between the positive and negative frequency components of the pulse spectrum during propagation, a feature that the slowly-varying envelope approximation is unable to capture. We therefore introduce a conceptually new model, based on the envelope of the analytic signal, that takes into account the full spectral dynamics of all frequency components, is prone to analytical treatment and retains the simulation efficiency of the nonlinear Schrodinger equation. We use our new equation to derive from first principles the phase-matching condition of the negative-frequency resonant radiation observed in previously reported experiments. (C) 2013 Optical Society of America

DNA hybridization assay at individual, biofunctionalized zinc oxide nanowires

Christian Leiterer, Barbara Seise, Irma Slowik, Gerald Broenstrup, Raphael Niepelt, Karina Weber, Carsten Ronning, Silke Christiansen, Wolfgang Fritzsche

Reliable and efficient identification of DNA is a major goal in on-site diagnostics. One dimensional nanostructures like nanowires (NW) represent potential sensor structures due to their extreme surface-to-bulk ratio, enabling enhanced biomolecule binding which results in optimal signals. While silicon NW are already well studied, NW made from other materials with promising properties like ZnO are not yet established as NW sensor material for bioanalytics. Here we demonstrate the DNA functionalization of ZnO NW even at the single NW level and their successful application in a DNA hybridization assay. ((c) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Improved efficiency of photoconductive THz emitters by increasing the effective contact length of electrodes

Abhishek Singh, Harshad Surdi, V. V. Nikesh, S. S. Prabhu, G. H. Doehler

We study the effect of a surface modification at the interface between metallic electrodes and semiconducting substrate in Semi-Insulating GaAs (SI-GaAs) based photoconductive emitters (PCE) on the emission of Tera-Hertz (THz) radiation. We partially etch out a 500 nm thick layer of SI-GaAs in grating like pattern with various periods before the contact deposition. By depositing the electrodes on the patterned surface, the electrodes follow the contour of the grating period. This increases the effective contact length of the electrodes per unit area of the active regions on the PCE. The maxima of the electric field amplitude of the THz pulses emitted from the patterned surface are enhanced by up to more than a factor 2 as compared to an un-patterned surface. We attribute this increase to the increase of the effective contact length of the electrode due to surface patterning. (C) 2013 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

PHz-wide Supercontinua of Nondispersing Subcycle Pulses Generated by Extreme Modulational Instability

F. Tani, J. C. Travers, P. St. J. Russell

Modulational instability (MI) of 500 fs, 5 mu J pulses, propagating in gas-filled hollow-core kagome photonic crystal fiber, is studied numerically and experimentally. By tuning the pressure and launched energy, we control the duration of the pulses emerging as a consequence of MI and hence are able to study two regimes: the classical MI case leading to few-cycle solitons of the nonlinear Schrodinger equation; and an extreme case leading to the formation of nondispersing subcycle pulses (0.5 to 2 fs) with peak intensities of order 10(14) Wcm(-2). Insight into the two regimes is obtained using a novel statistical analysis of the soliton parameters. Numerical simulations and experimental measurements show that, when a train of these pulses is generated, strong ionization of the gas occurs. This extreme MI is used to experimentally generate a high energy (> 1 mu J) and spectrally broad supercontinuum extending from the deep ultraviolet (320 nm) to the infrared (1300 nm).

Extraction of plasticity parameters of GaN with high temperature, in situ micro-compression

J. M. Wheeler, C. Niederberger, C. Tessarek, S. Christiansen, J. Michler

Micro-pillar compression has been utilised in a novel elevated temperature technique, in situ in the SEM to characterise the plasticity of gallium nitride (GaN) {0001}-oriented euhedral prisms grown by metallorganic vapor phase epitaxy. Electron backscatter diffraction was used to confirm the orientation of the prisms, and deformation was observed to occur via 2nd order pyramidal slip on the (11 (2) over bar2)(11 (2) over bar3) slip system. Analysis of the micro-compression data allowed extraction of fundamental deformation parameters of GaN from 24.5 to 479.3 degrees C. The strain rate sensitivity parameter was determined to be 0.0234 +/- 0.0073 both by constant strain rate micro-compressions and micro-compression strain rate jump tests. The measured activation volume was 3.88 +/- 0.13 x 10(-29) m(3), and the activation energy was 0.9 +/- 0.2 eV. (c) 2012 Elsevier Ltd. All rights reserved.

Optimal working points for continuous-variable quantum channels

Imran Khan, Christoffer Wittmann, Nitin Jain, Nathan Killoran, Norbert Luetkenhaus, Christoph Marquardt, Gerd Leuchs

The most important ability of a quantum channel is to preserve the quantum properties of transmitted quantum states. We experimentally demonstrate a continuous-variable system for efficient benchmarking of quantum channels. We probe the tested quantum channels for a wide range of experimental parameters such as amplitude, phase noise, and channel lengths up to 40 km. The data is analyzed using the framework of effective entanglement. We subsequently are able to deduce an optimal point of operation for each quantum channel with respect to the rate of distributed entanglement. This procedure is a promising candidate for benchmarking quantum nodes and individual links in large quantum networks of different physical implementations.

Sizing up entanglement in mutually unbiased bases with Fisher information

J. Rehacek, Z. Hradil, A. B. Klimov, G. Leuchs, L. L. Sanchez-Soto

An efficient method for assessing the quality of quantum state tomography is developed. Special attention is paid to the tomography of multipartite systems in terms of unbiased measurements. Although the overall reconstruction errors of different sets of mutually unbiased bases are the same, differences appear when particular aspects of the measured system are contemplated. This point is illustrated by estimating the fidelities of genuinely tripartite entangled states.

An optimized photon pair source for quantum circuits

Georg Harder, Vahid Ansari, Benjamin Brecht, Thomas Dirmeier, Christoph Marquardt, Christine Silberhorn

We implement an ultrafast pulsed type-II parametric down conversion source in a periodically poled KTP waveguide at telecommunication wavelengths with almost identical properties between signal and idler. As such, our source resembles closely a pure, genuine single mode photon pair source with indistinguishable modes. We measure the joint spectral intensity distribution and second order correlation functions of the marginal beams and find with both methods very low effective mode numbers corresponding to a Schmidt number below 1.16. We further demonstrate the indistinguishability as well as the purity of signal and idler photons by Hong-Ou-Mandel interferences between signal and idler and between signal/idler and a coherent field, respectively. Without using narrowband spectral filtering, we achieve a visibility for the interference between signal and idler of 94.8% and determine a purity of more than 80% for the heralded single photon states. Moreover, we measure raw heralding efficiencies of 20.5% and 15.5% for the signal and idler beams corresponding to detector-loss corrected values of 80% and 70%. (C) 2013 Optical Society of America

Classical optics representation of the quantum mechanical translation operator via ABCD matrices

Marco Ornigotti, Andrea Aiello

The ABCD matrix formalism describing paraxial propagation of optical beams across linear systems is generalized to arbitrary beam trajectories. As a by-product of this study, a one-to-one correspondence between the extended ABCD matrix formalism presented here and the quantum mechanical translation operator is established.

One-Step Synthesis of PEG-Coated Gold Nanoparticles by Rapid Microwave Heating

Seung Kwon Seol, Daeho Kim, Sunshin Jung, Won Suk Chang, Ji Tae Kim

Polyethylene Glycol-(PEG-) coated gold nanoparticles (PEG-AuNPs) are synthesized by a one-step route with rapid microwave heating. Homogeneous nucleation of the primary gold particles is enhanced by increasing the applied microwave power during the initial stage of the synthesis, increasing the temperature ramping rate (R-r) and resulting in decreased size and improved uniformity of the synthesized PEG-AuNPs. Using rapid microwave heating, we successfully produce uniform colloidal PEG-AuNPs with an average diameter of 14.3 +/- 2.5 nm within a few minutes. By appropriate tuning of the growth parameters, microwave synthesis can produce largely colloidal PEG-AuNPs with high uniformity.

Long-distance laser propulsion and deformation-monitoring of cells in optofluidic photonic crystal fiber

Sarah Unterkofler, Martin K. Garbos, Tijmen G. Euser, Philip St. J. Russell

We introduce a unique method for laser-propelling individual cells over distances of 10s of cm through stationary liquid in a microfluidic channel. This is achieved by using liquid-filled hollow-core photonic crystal fiber (HC-PCF). HC-PCF provides low-loss light guidance in a well-defined single mode, resulting in highly uniform optical trapping and propulsive forces in the core which at the same time acts as a microfluidic channel. Cells are trapped laterally at the center of the core, typically several microns away from the glass interface, which eliminates adherence effects and external perturbations. During propagation, the velocity of the cells is conveniently monitored using a non-imaging Doppler velocimetry technique. Dynamic changes in velocity at constant optical powers up to 350 mW indicate stress-induced changes in the shape of the cells, which is confirmed by bright-field microscopy. Our results suggest that HC-PCF will be useful as a new tool for the study of single-cell biomechanics. ((c) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Soliton-radiation trapping in gas-filled photonic crystal fibers

Mohammed F. Saleh, Fabio Biancalana

We propose an optical trapping technique in which a fundamental soliton traps an ultrashort small amplitude radiation in a symmetric hollow-core photonic crystal fiber filled with a noble gas, preventing its dispersion. The system is Raman- and plasma-free. Trapping is due to the cross phase modulation effect between the two pulses. The trapped radiation inside the soliton-induced potential will oscillate periodically due to the shock effect, similar to the motion of a mechanical pendulum. DOI: 10.1103/PhysRevA.87.043807

Orbital angular momentum from marginals of quadrature distributions

L. L. Sanchez-Soto, A. B. Klimov, P. de la Hoz, I. Rigas, J. Rehacek, Z. Hradil, G. Leuchs

We set forth a method to analyze the orbital angular momentum of a light field. Instead of using the canonical formalism for the conjugate pair angle-angular momentum, we model this latter variable by the superposition of two independent harmonic oscillators along two orthogonal axes. By describing each oscillator by a standard Wigner function, we derive, via a consistent change of variables, a comprehensive picture of the orbital angular momentum. We compare this with previous approaches and show how this method works in some relevant examples.

High-energy, shock-front-assisted resonant radiation in the normal dispersion regime

Thomas Roger, Mohammed F. Saleh, Samudra Roy, Fabio Biancalana, Chunyong Li, Daniele Faccio

We present a simple yet effective theory that predicts the existence of resonant radiation bands in the deep normal group-velocity dispersion region of a medium, even in the absence of a zero-group-velocity dispersion point. This radiation is evident when the medium is pumped with high-energy ultrashort pulses, and it is driven by the interplay between the Kerr and the shock terms in the nonlinear Schrodinger equation. Accurate experiments performed in bulk silica fully support the theoretical phase-matching condition found by our theory.

Tunable vacuum-UV to visible ultrafast pulse source based on gas-filled Kagome-PCF

Ka Fai Mak, John C. Travers, Philipp Hoelzer, Nicolas Y. Joly, Philip St. J. Russell

An efficient and tunable 176-550 nm source based on the emission of resonant dispersive radiation from ultrafast solitons at 800 nm is demonstrated in a gas-filled hollow-core photonic crystal fiber (PCF). By careful optimization and appropriate choice of gas, informed by detailed numerical simulations, we show that bright, high quality, localized bands of UV light (relative widths of a few percent) can be generated at all wavelengths across this range. Pulse energies of more than 75 nJ in the deep-UV, with relative bandwidths of similar to 3%, are generated from pump pulses of a few mu J. Excellent agreement is obtained between numerical and experimental results. The effects of positive and negative axial pressure gradients are also experimentally studied, and the coherence of the deep-UV dispersive wave radiation numerically investigated. (C) 2013 Optical Society of America

Detection of Single Nanoparticles and Lentiviruses Using Microcavity Resonance Broadening

Linbo Shao, Xue-Feng Jiang, Xiao-Chong Yu, Bei-Bei Li, William R. Clements, Frank Vollmer, Wei Wang, Yun-Feng Xiao, Qihuang Gong

A new label-free sensing mechanism is demonstrated experimentally by monitoring the whispering-gallery mode broadening in microcavities. It is immune to both noise from the probe laser and environmental disturbances, and is able to remove the strict requirement for ultra-high-Q mode cavities for sensitive nanoparticle detection. This ability to sense nanoscale objects and biological analytes is particularly crucial for wide applications.

Nonclassical features of the polarization quasiprobability distribution

M. V. Chekhova, F. Ya. Khalili

Polarization quasiprobability distribution is defined in the space of the Stokes observables. It can be reconstructed with the help of polarization quantum tomography and provides a full description of the so-called polarization sector of quantum states of light. We show here that due to its definition in terms of the discrete-valued Stokes operators, polarization quasiprobability distribution has singularities at integer values of the Stokes observables and takes negative values even for the quantum states typically considered as "classical" ones. In experiments with "bright" multiphoton states, the photon-number resolution is smeared due to the photodetectors' technical limitations. In this case, nonclassical features of the explored quantum states can be revealed by adding a strong coherent beam into the orthogonal polarization.

Spectral broadening in Brillouin imaging

Giuseppe Antonacci, Matthew R. Foreman, Carl Paterson, Peter Toeroek

Brillouin microscopy is an emerging imaging modality that provides fundamental information about mechanical properties of media in a non-contact manner. To date, low numerical aperture (NA) optics have been used, due to noticeable angular broadening of the Brillouin spectrum at higher NAs. In this work, we investigate theoretically and experimentally the dependence of spectral broadening effects in Brillouin imaging on system NA, for both 90 degrees and 180 degrees scattering geometries. Lineshape deformations and broadening are found to be minimised in a backscattering geometry, hence paving the way for high resolution in-vivo mechanical imaging. (C) 2013 AIP Publishing LLC.

Fourth-order dispersion mediated modulation instability in dispersion oscillating fibers

Maxime Droques, Alexandre Kudlinski, Geraud Bouwmans, Gilbert Martinelli, Arnaud Mussot, Andrea Armaroli, Fabio Biancalana

We investigate the role played by fourth-order dispersion on the modulation instability process in dispersion oscillating fibers. It not only leads to the appearance of instability sidebands in the normal dispersion regime (as in uniform fibers), but also to a new class of large detuned instability peaks that we ascribe to the variation of dispersion. All these theoretical predictions are experimentally confirmed. (C) 2013 Optical Society of America

Effects of squeezed-film damping on the optomechanical nonlinearity in dual-nanoweb fiber

J. R. Koehler, A. Butsch, T. G. Euser, R. E. Noskov, P. St. J. Russell

The freely-suspended glass membranes in a dual-nanoweb fiber, driven at resonance by intensity-modulated light, exhibit a giant optomechanical nonlinearity. We experimentally investigate the effect of squeezed-film damping by exploring the pressure dependence of resonant frequency and mechanical quality factor. As a consequence of the unusually narrow slot between the nanowebs (22 mu m by 550nm), the gas-spring effect causes a pressure-dependent frequency shift that is similar to 15 times greater than typically measured in micro-electro-mechanical devices. When evacuated, the dual-nanoweb fiber yields a quality factor of similar to 3 600 and a resonant optomechanical nonlinear coefficient that is similar to 60 000 times larger than the Kerr effect. (C) 2013 AIP Publishing LLC.

Total absorption of light by a nanoparticle: an electromagnetic sink in the optical regime

A. Sentenac, P. C. Chaumet, G. Leuchs

In this Letter, we give a general description of the illumination and object properties for obtaining total absorption. We show theoretically and numerically that properly designed sub-100 nm metallic particles are able to absorb all the energy of an incident beam if the latter is adequately shaped. In addition to their interest as absorbers, these particles act as efficient near-field probes as they convert the incident propagating beam into a localized nonradiative field. (C) 2013 Optical Society of America

Macroscopic Hong-Ou-Mandel interference

T. Sh Iskhakov, K. Yu Spasibko, M. V. Chekhova, G. Leuchs

We report on a Hong-Ou-Mandel interference experiment for twin beams with photon numbers per mode as large as 10(6) generated via high-gain parametric down conversion (PDC). The standard technique of coincidence counting leads in this case to a dip with a very low visibility. By measuring, instead of coincidence counting rate, the variance of the photon-number difference, we observe an extremely well-pronounced peak. From the shape of the peak, one can infer information about the spectral properties of the PDC radiation, including the number of frequency/temporal modes.

Kinetic study of H-terminated silicon nanowires oxidation in very first stages

Muhammad Y. Bashouti, Kasra Sardashti, Juergen Ristein, Silke Christiansen

Oxidation of silicon nanowires (Si NWs) is an undesirable phenomenon that has a detrimental effect on their electronic properties. To prevent oxidation of Si NWs, a deeper understanding of the oxidation reaction kinetics is necessary. In the current work, we study the oxidation kinetics of hydrogen-terminated Si NWs (H-Si NWs) as the starting surfaces for molecular functionalization of Si surfaces. H-Si NWs of 85-nm average diameter were annealed at various temperatures from 50A degrees C to 400A degrees C, in short-time spans ranging from 5 to 60 min. At high temperatures (T a parts per thousand yen 200A degrees C), oxidation was found to be dominated by the oxide growth site formation (made up of silicon suboxides) and subsequent silicon oxide self-limitation. Si-Si backbond oxidation and Si-H surface bond propagation dominated the process at lower temperatures (T < 200 degrees C).

Theory of quantum frequency conversion and type-II parametric down-conversion in the high-gain regime

Andreas Christ, Benjamin Brecht, Wolfgang Mauerer, Christine Silberhorn

Frequency conversion (FC) and type-II parametric down-conversion (PDC) processes serve as basic building blocks for the implementation of quantum optical experiments: type-II PDC enables the efficient creation of quantum states such as photon-number states and Einstein-Podolsky-Rosen (EPR)-states. FC gives rise to technologies enabling efficient atom-photon coupling, ultrafast pulse gates and enhanced detection schemes. However, despite their widespread deployment, their theoretical treatment remains challenging. Especially the multi-photon components in the high-gain regime as well as the explicit time-dependence of the involved Hamiltonians hamper an efficient theoretical description of these nonlinear optical processes. In this paper, we investigate these effects and put forward two models that enable a full description of FC and type-II PDC in the high-gain regime. We present a rigorous numerical model relying on the solution of coupled integro-differential equations that covers the complete dynamics of the process. As an alternative, we develop a simplified model that, at the expense of neglecting time-ordering effects, enables an analytical solution. While the simplified model approximates the correct solution with high fidelity in a broad parameter range, sufficient for many experimental situations, such as FC with low efficiency, entangled photon-pair generation and the heralding of single photons from type-II PDC, our investigations reveal that the rigorous model predicts a decreased performance for FC processes in quantum pulse gate applications and an enhanced EPR-state generation rate during type-II PDC, when EPR squeezing values above 12 dB are considered.

Observation of Defect States in PT-Symmetric Optical Lattices

Alois Regensburger, Mohammad-Ali Miri, Christoph Bersch, Jakob Naeger, Georgy Onishchukov, Demetrios N. Christodoulides, Ulf Peschel

We provide the first experimental demonstration of defect states in parity-time (PT) symmetric mesh-periodic potentials. Our results indicate that these localized modes can undergo an abrupt phase transition in spite of the fact that they remain localized in a PT-symmetric periodic environment. Even more intriguing is the possibility of observing a linearly growing radiation emission from such defects provided their eigenvalue is associated with an exceptional point that resides within the continuum part of the spectrum. Localized complex modes existing outside the band-gap regions are also reported along with their evolution dynamics.

Raman-free nonlinear optical effects in high pressure gas-filled hollow core PCF

M. Azhar, G. K. L. Wong, W. Chang, N. Y. Joly, P. St J. Russell

The effective Kerr nonlinearity of hollow-core kagome-style photonic crystal fiber (PCF) filled with argon gas increases to similar to 15% of that of bulk silica glass when the pressure is increased from 1 to 150 bar, while the zero dispersion wavelength shifts from 300 to 900 nm. The group velocity dispersion of the system is uniquely pressure-tunable over a wide range while avoiding Raman scattering-absent in noble gases-and having an extremely high optical damage threshold. As a result, detailed and well-controlled studies of nonlinear effects can be performed, in both normal and anomalous dispersion regimes, using only a fixed-frequency pump laser. For example, the absence of Raman scattering permits clean observation, at high powers, of the interaction between a modulational instability side-band and a soliton-created dispersive wave. Excellent agreement is obtained between numerical simulations and experimental results. The system has great potential for the realization of reconfigurable supercontinuum sources, wavelength convertors and short-pulse laser systems. (C)2013 Optical Society of America

Optical Activity in Twisted Solid-Core Photonic Crystal Fibers

X. M. Xi, T. Weiss, G. K. L. Wong, F. Biancalana, S. M. Barnett, M. J. Padgett, P. St. J. Russell

In this Letter we show that, in spectral regions where there are no orbital cladding resonances to cause transmission loss, the core mode of a continuously twisted photonic crystal fiber (PCF) exhibits optical activity, and that the magnitude of the associated circular birefringence increases linearly with twist rate and is highly reproducible. In contrast to previous work on twist-induced circular birefringence, PCF has zero linear birefringence and an on-axis core, making the appearance of circular birefringence rather unexpected. A theoretical model based on symmetry properties and perturbation theory is developed and used to show that both spin and orbital angular momentum play a role in this effect. It turns out that the degenerate left-and right-circularly polarized modes of the untwisted PCF are not 100% circularly polarized but carry a small amount of orbital angular momentum caused by the interaction between the core mode and the hollow channels. DOI:10.1103/PhysRevLett.110.143903

Dynamical generation of interwoven soliton trains by nonlinear emission in binary Bose-Einstein condensates

V. A. Brazhnyi, David Novoa, Chandroth P. Jisha

We propose a method for the generation of trains of alternating bright solitons in two-component Bose-Einstein condensates, using controlled emission of nonlinear matter waves in the uncoupled regime with spatially varying intraspecies interaction and out-of-phase oscillations of the ground states in the trap. Under this scheme, solitons are sequentially launched from the different components and interact with each other through phase-independent cross coupling. We obtain an analytical estimation of the critical condition for soliton emission using a geometric guiding model, in analogy with integrated optical systems. In addition, we show how strong initial perturbations in the system can trigger the spontaneous generation of supersolitons, i.e., localized phononlike excitations of the soliton trains. Finally, we demonstrate the controllable generation of slow and fast supersolitons by adding external localized potentials in the nonlinear region.

Diffractive Resonant Radiation Emitted by Spatial Solitons in Waveguide Arrays

Truong X. Tran, Fabio Biancalana

We study analytically and numerically the diffractive resonant radiation emitted by spatial solitons, which is generated in waveguide arrays with Kerr nonlinearity. The phase matching condition between solitons and radiation is derived and studied for the first time and agrees well with direct pulse propagation simulations. The folded dispersion due to the Brillouin zone leads to a peculiar anomalous soliton recoil that we describe in detail. DOI: 10.1103/PhysRevLett.110.113903

The polarization properties of a tilted polarizer

Jan Korger, Tobias Kolb, Peter Banzer, Andrea Aiello, Christoffer Wittmann, Christoph Marquardt, Gerd Leuchs

Polarizers are key components in optical science and technology. Thus, understanding the action of a polarizer beyond oversimplifying approximations is crucial. In this work, we study the interaction of a polarizing interface with an obliquely incident wave experimentally. To this end, a set of Mueller matrices is acquired employing a novel procedure robust against experimental imperfections. We connect our observation to a geometric model, useful to predict the effect of polarizers on complex light fields. (C) 2013 Optical Society of America

Efficient coupling to an optical resonator by exploiting time-reversal symmetry

M. Bader, S. Heugel, A. L. Chekhov, M. Sondermann, G. Leuchs

The interaction of a cavity with an external field is symmetric under time reversal. Thus, coupling to a resonator is most efficient when the incident light is the time reversed version of a free cavity decay, i.e. when it has a rising exponential shape matching the cavity lifetime. For light entering the cavity from only one side, the maximally achievable coupling efficiency is limited by the choice of the cavity mirrors' reflectivities. Such an empty-cavity experiment serves also as a model system for single-photon single-atom absorption dynamics. We present experiments coupling exponentially rising pulses to a cavity system which allows for high coupling efficiencies. The influence of the time constant of the rising exponential is investigated as well as the effect of a finite pulse duration. We demonstrate coupling 94% of the incident TEM00 mode into the resonator.

Mode-based microparticle conveyor belt in air-filled hollow-core photonic crystal fiber

Oliver A. Schmidt, Tijmen G. Euser, Philip St. J. Russell

We show how microparticles can be moved over long distances and precisely positioned in a low-loss air-filled hollow-core photonic crystal fiber using a coherent superposition of two co-propagating spatial modes, balanced by a backward-propagating fundamental mode. This creates a series of trapping positions spaced by half the beat-length between the forward-propagating modes (typically a fraction of a millimeter). The system allows a trapped microparticle to be moved along the fiber by continuously tuning the relative phase between the two forward-propagating modes. This mode-based optical conveyor belt combines long-range transport of microparticles with a positional accuracy of 1 mu m. The technique also has potential uses in waveguide-based optofluidic systems. (C)2013 Optical Society of America

Compensation of anisotropy effects in a nonlinear crystal for squeezed vacuum generation

A. M. Perez, F. Just, A. Cavanna, M. V. Chekhova, G. Leuchs

Squeezed vacuum can be obtained by an optical parametric amplifier (OPA) with the quantum vacuum state at the input. We are interested in a degenerate type-I OPA based on parametric down-conversion (PDC) where, due to phase matching requirements, an extraordinary polarized pump must impinge onto a birefringent crystal with a large chi((2)) nonlinearity. As a consequence of the optical anisotropy of the medium, the spatial spectrum of the generated radiation is affected by the transverse walk-off. In this work we describe a method that reduces the spatial distortions, by using two consecutive crystals instead of one. We show that after anisotropy compensation the two-photon amplitude becomes symmetric, allowing for a simple Schmidt expansion, a procedure that in practice requires states that come from experimental systems free of anisotropy effects. Qualitative experimental observations are made for the case of high-gain PDC.

Nonlinear optics in Xe-filled hollow-core PCF in high pressure and supercritical regimes

M. Azhar, N. Y. Joly, J. C. Travers, P. St J. Russell

Supercritical Xe at 293 K offers a Kerr nonlinearity that can exceed that of fused silica while being free of Raman scattering. It also has a much higher optical damage threshold and a transparency window that extends from the UV to the infrared. We report the observation of nonlinear phenomena, such as self-phase modulation, in hollow-core photonic crystal fiber filled with supercritical Xe. In the subcritical regime, intermodal four-wave mixing resulted in the generation of UV light in the HE12 mode. The normal dispersion of the fiber at high pressures means that spectral broadening can be clearly obtained without influence from soliton effects or material damage.

Subwavelength solitons and Faraday waves in two-dimensional lattices of metal nanoparticles

Roman E. Noskov, Daria A. Smirnova, Yuri S. Kivshar

We demonstrate that optically driven two-dimensional lattices of nonlinear metal nanoparticles can support a variety of dissipative localized modes including Faraday ripples, trapped and walking solitons, oscillons, and switching waves connecting different polarization states. (C) 2013 Optical Society of America

Antennas, quantum optics and near-field microscopy

Vahid Sandoghdar, Mario Agio, Xue-Wen Chen, Stephan Götzinger, Kwang-Geol Lee

The atom is the most elementary constituent of any model that describes the quantum nature of light–matter interaction. Because atoms emit and absorb light at well-defined frequencies, nineteenth century scientists thought of them as collections of harmonically oscillating electric dipole moments or EHDs. In the language of modern physics, the latter represent dipolar transitions among the various quantum mechanical states of an atom.<br><br>In a strict definition, the field of quantum optics deals with problems that not only require the quantization of matter but also of the electromagnetic field, with examples such as (i) generation of squeezed light or Fock states, (ii) strong coupling of an atom and a photon, (iii) entanglement of a photon with an atom and (iv) Casimir and van der Waals forces. There are also many other important topics that have been discussed within the quantum optics community but do not necessarily require a full quantum electrodynamic (QED) treatment. Examples are (i) cooling and trapping of atoms, (ii) precision spectroscopy and (iii) modification of spontaneous emission.<br><br>The simple picture of a TLS as an EHD remains very insightful and valuable to this day. Indeed, much of what we discuss in this chapter has to do with the interplay between the quantum and classical mechanical characters of dipolar oscillators. For instance, the extinction cross-section of a TLS, given by 3λ2/2π, can be derived just as well using quantum mechanics [70] or classical optics [234]. Another example, albeit more subtle, concerns the spontaneous emission rate.

Multipolar hierarchy of efficient quantum polarization measures

P. de la Hoz, A. B. Klimov, G. Bjork, Y. -H. Kim, C. Mueller, Ch. Marquardt, G. Leuchs, L. L. Sanchez-Soto

We advocate a simple multipole expansion of the polarization density matrix. The resulting multipoles appear as successive moments of the Stokes variables and can be obtained from feasible measurements. In terms of these multipoles we construct a whole hierarchy of measures that accurately assess higher-order polarization fluctuations.

Distributing Entanglement with Separable States

Christian Peuntinger, Vanessa Chille, Ladislav Mista Jr., Natalia Korolkova, Michael Foertsch, Jan Korger, Christoph Marquardt, Gerd Leuchs

We experimentally demonstrate a protocol for entanglement distribution by a separable quantum system. In our experiment, two spatially separated modes of an electromagnetic field get entangled by local operations, classical communication, and transmission of a correlated but separable mode between them. This highlights the utility of quantum correlations beyond entanglement for the establishment of a fundamental quantum information resource and verifies that its distribution by a dual classical and separable quantum communication is possible.

Quantum repeaters and quantum key distribution: Analysis of secret-key rates

Silvestre Abruzzo, Sylvia Bratzik, Nadja K. Bernardes, Hermann Kampermann, Peter van Loock, Dagmar Bruss

We analyze various prominent quantum repeater protocols in the context of long-distance quantum key distribution. These protocols are the original quantum repeater proposal by Briegel, Dur, Cirac and Zoller, the so-called hybrid quantum repeater using optical coherent states dispersively interacting with atomic spin qubits, and the Duan-Lukin-Cirac-Zoller-type repeater using atomic ensembles together with linear optics and, in its most recent extension, heralded qubit amplifiers. For our analysis, we investigate the most important experimental parameters of every repeater component and find their minimally required values for obtaining a nonzero secret key. Additionally, we examine in detail the impact of device imperfections on the final secret key rate and on the optimal number of rounds of distillation when the entangled states are purified right after their initial distribution.

Highly efficient coupling from an optical fiber to a nanoscale silicon optomechanical cavity

Simon Groeblacher, Jeff T. Hill, Amir H. Safavi-Naeini, Jasper Chan, Oskar Painter

We demonstrate highly efficient coupling of light from an optical fiber to a silicon photonic crystal optomechanical cavity. The fiber-to-cavity coupling utilizes a compact ( L approximate to 25 mu m) intermediate adiabatic coupler. The optical coupling is lithographically controlled, broadband, relatively insensitive to fiber misalignment and allows for light to be transferred from an optical fiber to, in principle, any photonic chip with refractive index greater than that of the optical fiber. Here we demonstrate single-sided cavity coupling with a total fiber-to-cavity optical power coupling efficiency of 85%. (c) 2013 AIP Publishing LLC.

Oxide-free hybrid silicon nanowires: From fundamentals to applied nanotechnology

Muhammad Y. Bashouti, Kasra Sardashti, Sebastian W. Schmitt, Matthias Pietsch, Juergen Ristein, Hossam Haick, Silke H. Christiansen

The ability to control physical properties of silicon nanowires (Si NWs) by designing their surface bonds is important for their applicability in devices in the areas of nano-electronics, nano-photonics, including photovoltaics and sensing. In principle a wealth of different molecules can be attached to the bare Si NW surface atoms to create e.g. Si-O, Si-C, Si-N, etc. to mention just the most prominent ones. Si-O bond formation, i.e. oxidation usually takes place automatically as soon as Si NWs are exposed to ambient conditions and this is undesired is since a defective oxide layer (i.e. native silicon dioxide - SiO2) can cause uncontrolled trap states in the band gap of silicon. Surface functionalization of Si NW surfaces with the aim to avoid oxidation can be carried out by permitting e.g. Si-C bond formation when alkyl chains are covalently attached to the Si NW surfaces by employing a versatile two-step chlorination/alkylation process that does not affect the original length and diameter of the NWs. Termination of Si NWs with alkyl molecules through covalent Si-C bonds can provide long term stability against oxidation of the Si NW surfaces. The alkyl chain length determines the molecular coverage of Si NW surfaces and thus the surface energy and next to simple Si-C bonds even bond types such as C=C and C=C can be realized. When integrating differently functionalized Si NWs in functional devices such as field effect transistors (FETs) and solar cells, the physical properties of the resultant devices vary. (C) 2013 Elsevier Ltd. All rights reserved.

Causal signal transmission by quantum fields. VI: The Lorentz condition and Maxwell's equations for fluctuations of the electromagnetic field

L. I. Plimak, S. Stenholm

The general structure of electromagnetic interactions in the so-called response representation of quantum electrodynamics (QED) is analysed. A formal solution to the general quantum problem of the electromagnetic field interacting with matter is found. Independently, a formal solution to the corresponding problem in classical stochastic electrodynamics (CSED) is constructed. CSED and QED differ only in the replacement of stochastic averages of c-number fields and currents by time-normal averages of the corresponding Heisenberg operators. All relations of QED connecting quantum field to quantum current lack Planck's constant, and thus coincide with their counterparts in CSED. In Feynman's terms, one encounters complete disentanglement of the potential and current operators in response picture. Based on this parallelism between QED and CSED, it is natural to expect validity of the Lorentz condition and Maxwell's equations for the time-normal averages of the potential and current. Things however turn out to be more complicated. Maxwell's equations under the time-normal ordering can only be demonstrated subject to cancellation of the so-called Schwinger terms by gauge-invariant regularisations. We presume this pattern to be general, formulating this as "commutativity conjecture". Consistency of the latter with the Heisenberg uncertainty principle is discussed. (C) 2013 Elsevier Inc. All rights reserved.

Mode structure and polaritonic contributions to the Casimir effect in a magnetodielectric cavity

Harald R. Haakh, Francesco Intravaia

We present a full analysis of the mode spectrum in a cavity formed by two parallel plates, one of which is magnetodielectric (metamaterial) while the other one is metallic, and obtain dispersion relations in closed form. The optical properties of the cavity walls are described in terms of realistic models for effective permittivity and permeability. Surface polaritons, i.e., electromagnetic modes that have at least partly an evanescent character, are shown to dominate the Casimir interaction at small separations. We analyze in detail the s-polarized polaritons, which are a characteristic feature of a magnetodielectric configuration, and discuss their role in the repulsive Casimir force.

Amplification of higher-order modes by stimulated Raman scattering in H-2-filled hollow-core photonic crystal fiber

B. M. Trabold, A. Abdolvand, T. G. Euser, A. M. Walser, P. St. J. Russell

We report a method for amplifying higher-order guided modes, synthesized with a spatial light modulator, in a hydrogen-filled hollow-core photonic crystal fiber. The gain mechanism is intermodal stimulated Raman scattering, a pump laser source in the fundamental mode providing amplification for weak higher-order seed modes at the Stokes frequency. The gain for higher-order modes up to LP31 is calculated and verified experimentally. (C) 2013 Optical Society of America

The Role of Hole Transport in Hybrid Inorganic/Organic Silicon/Poly(3,4-ethylenedioxy-thiophene):Poly(styrenesulfonate) Heterojunction Solar Cells

Matthias Pietsch, Muhammad Y. Bashouti, Silke Christiansen

In this paper, the fundamental advantage of highly conductive transparent polymers as hole transport layers in hybrid solar cells is demonstrated. The substantial efficiency improvement of hybrid n-type silicon (n-Si)/poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS) solar cells by adding organic solvents to the polymer dispersion is investigated, and a model that explains reasons and mechanisms for that improvement is given. Open-circuit voltages of 600 mV were measured, which are comparable to conventional diffused silicon pn-junction wafer cells. It is shown by means of X-ray photoelectron spectroscopy that the PEDOT versus PSS ratio plays an important role for charge carrier transport in the PEDOT:PSS layer as well as for charge carrier separation at the n-Si/PEDOT:PSS interface. A shell of insulating PSS segregates at the surface of PEDOT:PSS grains and represents a considerable barrier for charge carrier transport and charge carrier separation, influencing the conductivity of the polymer film and the open-circuit voltage of a processed solar cell, respectively. It could be demonstrated that a mixing of the PEDOT:PSS polymer blend with the organic solvent dimethylsulfoxide reduces the PSS insulator segregation at the surface of PEDOT:PSS grains and improves the performance of hybrid n-Si/PEDOT:PSS solar cells.

A Time-Resolved Numerical Study of the Vapor-Liquid-Solid Growth Kinetics Describing the Initial Nucleation Phase as well as Pulsed Deposition Processes

Bjoern Eisenhawer, Vladimir Sivakov, Silke Christiansen, Fritz Falk

Today, the vapor liquid solid (VLS) growth mechanism is a common process for the metal catalyzed bottom-up growth of semiconductor nanowires (NWs). Nevertheless, most of the literature only is concerned with the steady-state NW growth which applies when the amount of material supplied is equal to the amount consumed by the NW growth at the same time. While this description is suitable for chemical vapor deposition (CVD) or electron beam evaporation (EBE) processes after the initial nucleation time, problems arise when pulsed growth processes like pulsed laser deposition (PLD) are used since in this case the steady state growth condition cannot be applied. Moreover, the initial phase of NW growth cannot be described with steady state growth conditions, either. In this work, we present a modeling approach for VLS NW growth based on numerical simulations, which is capable of describing the nucleation phase of the VLS growth process as well as a pulsed deposition process.

From Arrays of THz Antennas to Large-Area Emitters

Gottfried H. Doehler, Luis Enrique Garcia-Munoz, Sascha Preu, Stefan Malzer, Sebastian Bauerschmidt, Javier Montero-de-Paz, Eduardo Ugarte-Munoz, Alejandro Rivera-Lavado, Vicente Gonzalez-Posadas, et al.

Arrays of coherently driven photomixers with antenna (antenna emitter arrays, AEAs) have been evaluated as a possibility to overcome the power limitations of individual conventional photomixers with antenna ("antenna emitters", AEs) for the generation of continuous-wave (CW) THz radiation. In this paper, "large area emitters" (LAEs) are proposed as an alternative approach, and compared with AEAs. In this antenna-free new scheme of photomixing, the THz radiation originates directly from the acceleration of photo-induced charge carriers generated within a large semiconductor area. The quasi-continuous distribution of emitting elements corresponds to a high-density array and results in favorable radiation profiles without side lobes. Moreover, the achievable THz power is expected to outnumber even large AEAs. Last not least, the technological challenge of fabricating LAEs appears to be significantly less demanding.

Nonlinear amplification of side-modes in frequency combs

R. A. Probst, T. Steinmetz, T. Wilken, H. Hundertmark, S. P. Stark, G. K. L. Wong, P. St. J. Russell, T. W. Haensch, R. Holzwarth, et al.

We investigate how suppressed modes in frequency combs are modified upon frequency doubling and self-phase modulation. We find, both experimentally and by using a simplified model, that these side-modes are amplified relative to the principal comb modes. Whereas frequency doubling increases their relative strength by 6 dB, the growth due to self-phase modulation can be much stronger and generally increases with nonlinear propagation length. Upper limits for this effect are derived in this work. This behavior has implications for high-precision calibration of spectrographs with frequency combs used for example in astronomy. For this application, Fabry-Perot filter cavities are used to increase the mode spacing to exceed the resolution of the spectrograph. Frequency conversion and/or spectral broadening after non-perfect filtering reamplify the suppressed modes, which can lead to calibration errors. (C) 2013 Optical Society of America

Measurement-induced optical Kerr interaction

Seckin Sefi, Vishal Vaibhav, Peter van Loock

We present a method for implementing a weak optical Kerr interaction (single-mode Kerr Hamiltonian) in a measurement-based fashion using the common set of universal elementary interactions for continuous-variable quantum computation. Our scheme is a conceptually distinct alternative to the use of naturally occurring, weak Kerr nonlinearities or specially designed nonlinear media. Instead, we propose to exploit suitable off-line prepared quartic ancilla states together with beam splitters, squeezers, and homodyne detectors. For perfect ancilla states and ideal operations, our decompositions for obtaining the measurement-based Kerr Hamiltonian lead to a realization with near-unit fidelity. Nonetheless, even by using only approximate ancilla states in the form of superposition states of up to four photons, high fidelities are still attainable. Our scheme requires four elementary operations and its deterministic implementation corresponds to about 10 ancilla-based gate teleportations. We test our measurement-based Kerr interaction against an ideal Kerr Hamiltonian by applying them both to weak coherent states and single-photon superposition states.

The photonic wheel - demonstration of a state of light with purely transverse angular momentum

P. Banzer, M. Neugebauer, A. Aiello, C. Marquardt, N. Lindlein, T. Bauer, G. Leuchs

In classical mechanics, a system may possess angular momentum which can be either transverse (e.g. in a spinning wheel) or longitudinal (e.g. for a spiraling seed falling from a tree) with respect to the direction of motion. However, for light, a typical massless wave system, the situation is less versatile. Photons are well-known to exhibit intrinsic angular momentum which is longitudinal only: the spin angular momentum defining the polarization and the orbital angular momentum associated with a spiraling phase front. Here we show that it is possible to generate a novel state of the light field that contains purely transverse angular momentum, the analogue of a spinning mechanical wheel. We realize this state by tight focusing of a polarization tailored light beam and measure it using an optical nano-probing technique. Such a novel state of the light field can find applications in optical tweezers and spanners where it allows for additional rotational degree of freedom not achievable in single-beam configurations so far.

Continuous-Wave Sub-THz Photonic Generation With Ultra-Narrow Linewidth, Ultra-High Resolution, Full Frequency Range Coverage and High Long-Term Frequency Stability

A. R. Criado, C. de Dios, E. Prior, G. H. Doehler, S. Preu, S. Malzer, H. Lu, A. C. Gossard, P. Acedo

We report on a photonic system for generation of high quality continuous-wave (CW) sub-THz signals. The system consists on a gain-switching-based optical frequency comb generator (GS-OFCG), a two-optical-modes selection mechanism and a n-i-pn-i-p superlattice photomixer. As mode selection mechanism, both selective tunable optical filtering using Fabry-Perot tunable filters (FPTFs) and Optical Injection Locking (OIL) are evaluated. The performance of the reported system surpasses in orders of magnitude the performance of any commercially available optical mm-wave and sub-THz generation system in a great number of parameters. It matches and even overcomes those of the best commercially available electronic THz generation systems. The performance parameters featured by our system are: linewidth 10 Hz at 120 GHz, complete frequency range coverage (60-140 GHz) with a resolution in the order of 0.1 Hz at 120 GHz (10 of generated frequency), high long term frequency stability (5 Hz deviation over one hour). Most of these values are limited by the measurement instrumentation accuracy and resolution, thus the actual values of the system could be better than the reported ones. The frequency can be extended straightforwardly up to 1 THz extending the OFCG frequency span. This system is compact, robust, reliable, offers a very high performance, especially suited for sub-THz photonic local oscillators and high resolution spectroscopy.

Directional emission of dielectric disks with a finite scatterer in the THz regime

S. Preu, S. I. Schmid, F. Sedlmeir, J. Evers, H. G. L. Schwefel

In the Terahertz (THz) domain, we investigate both numerically and experimentally the directional emission of whispering gallery mode resonators that are perturbed by a small scatterer in the vicinity of the resonators rim. We determine quality factor degradation, the modal structure and the emission direction for various geometries. We find that scatterers do allow for directional emission without destroying the resonator's quality factor. This finding allows for new geometries and outcoupling scenarios for active whispering gallery mode structures such as quantum cascade lasers and passive resonators such as evanescent sensors. The experimental results agree well with finite difference time domain simulations. (C) 2013 Optical Society of America

Geometrical optimization and contact configuration in radial pn junction silicon nanorod and microrod solar cells

F. Voigt, T. Stelzner, S. Christiansen

Electric charge transport simulations of symmetrically doped radial pn junction silicon nanorod solar cells were performed using the Technology Computer-aided Design software suite by Silvaco. Two schemes of electric contacting were applied, the first one consisting of a cathode wrapped around the cladding of the rod and the second one in a cathode located only on the top rod surface. In both cases, the anode was implemented just below the bottom end of the p-type rod core. P-type cores and n-type shells of the rods were assumed, with dopant densities of 10(18)cm(-3) in both regions. The location of the pn junction was chosen such that well-formed space charge regions could be established with the outer end of the n-type depletion region being adjacent to the cylindric surface of the nanorod. Rod radii and rod lengths were varied and optimized in a three-step process for both types of contacting schemes. It was found that inhomogeneous carrier generation profiles diminish the open-circuit voltage in case of a wrapped cathode configuration. Most realistic is the usage of a top contact configuration with rod radii of 2 mu m and lengths of around 100 mu m, leading to a cell efficiency of about 15%. Further enhancement of performance is expected, if light trapping of the nanorod layer is taken into account and photonic light harvesting is applied. Copyright (c) 2012 John Wiley & Sons, Ltd.

Lightmatter interaction in free space

Gerd Leuchs, Markus Sondermann

We review recent experimental advances in the field of efficient coupling of single atoms and light in free space. Furthermore, a comparison of efficient free space coupling and strong coupling in cavity quantum electrodynamics (QED) is given. Free space coupling does not allow for observing oscillatory exchange between the light field and the atom which is the characteristic feature of strong coupling in cavity QED. Like cavity QED, free space QED does, however, offer full switching of the light field, a 180 degrees phase shift conditional on the presence of a single atom as well as 100% absorption probability of a single photon by a single atom. Furthermore, free space cavity QED comprises the interaction with a continuum of modes.

Increasing the Dimensionality of Quantum Walks Using Multiple Walkers

Peter P. Rohde, Andreas Schreiber, Martin Stefanak, Igor Jex, Alexei Gilchrist, Christine Silberhorn

We show that with the addition of multiple walkers, quantum walks on a line can be transformed into lattice graphs of higher dimension. Thus, multi-walker walks can simulate single-walker walks on higher dimensional graphs and vice versa. This exponential complexity opens up new applications for present-day quantum walk experiments. We discuss the applications of such higher-dimensional structures and how they relate to linear optics quantum computing. In particular we show that multi-walker quantum walks are equivalent to the BOSONSAMPLING model for linear optics quantum computation proposed by Aaronson and Arkhipov. With the addition of control over phase-defects in the lattice, which can be simulated with entangling gates, asymmetric lattice structures can be constructed which are universal for quantum computation.

Coherent Interaction of Light with a Metallic Structure Coupled to a Single Quantum Emitter: From Superabsorption to Cloaking

Xue-Wen Chen, Vahid Sandoghdar, Mario Agio

We provide a general theoretical platform based on quantized radiation in absorptive and inhomogeneous media for investigating the coherent interaction of light with material structures in the immediate vicinity of quantum emitters. In the case of a very small metallic cluster, we demonstrate extreme regimes where a single emitter can either counteract or enhance particle absorption by 3 orders of magnitude. For larger structures, we show that an emitter can eliminate both scattering and absorption and cloak a plasmonic antenna. We provide physical interpretations of our results and discuss their applications in active metamaterials and quantum plasmonics. DOI: 10.1103/PhysRevLett.110.153605

Passive mode-locking of fiber ring laser at the 337th harmonic using gigahertz acoustic core resonances

M. S. Kang, N. Y. Joly, P. St. J. Russell

We report the experimental demonstration of a passively mode-locked Er-doped fiber ring laser operating at the 337th harmonic (1.80 GHz) of the cavity. The laser makes use of highly efficient Raman-like optoacoustic interactions between the guided light and gigahertz acoustic resonances trapped in the micron-sized solid glass core of a photonic crystal fiber. At sufficient pump power levels the laser output locks to a repetition rate corresponding to the acoustic frequency. A stable optical pulse train with a side-mode suppression ratio higher than 45 dB was obtained at low pump powers (similar to 60 mW). (C) 2013 Optical Society of America

High-T-g TOPAS microstructured polymer optical fiber for fiber Bragg grating strain sensing at 110 degrees

Christos Markos, Alessio Stefani, Kristian Nielsen, Henrik K. Rasmussen, Wu Yuan, Ole Bang

We present the fabrication and characterization of fiber Bragg gratings (FBGs) in an endlessly single-mode microstructured polymer optical fiber (mPOF) made of humidity-insensitive high-Tg TOPAS cyclic olefin copolymer. The mPOF is the first made from grade 5013 TOPAS with a glass transition temperature of Tg = 135 degrees C and we experimentally demonstrate high strain operation (2.5%) of the FBG at 98 degrees C and stable operation up to a record high temperature of 110 degrees C. The Bragg wavelengths of the FBGs are around 860 nm, where the propagation loss is 5.1dB/m, close to the fiber loss minimum of 3.67dB/m at 787nm. (C) 2013 Optical Society of America

Two techniques for temporal pulse compression in gas-filled hollow-core kagome photonic crystal fiber

K. F. Mak, J. C. Travers, N. Y. Joly, A. Abdolvand, P. St. J. Russell

We demonstrate temporal pulse compression in gas-filled kagome hollow-core photonic crystal fiber (PCF) using two different approaches: fiber-mirror compression based on self-phase modulation under normal dispersion, and soliton effect self-compression under anomalous dispersion with a decreasing pressure gradient. In the first, efficient compression to near-transform-limited pulses from 103 to 10.6 fs was achieved at output energies of 10.3 mu J. In the second, compression from 24 to 6.8 fs was achieved at output energies of 6.6 mu J, also with near-transform-limited pulse shapes. The results illustrate the potential of kagome-PCF for postprocessing the output of fiber lasers. We also show that, using a negative pressure gradient, ultrashort pulses can be delivered directly into vacuum. (C) 2013 Optical Society of America

Creation and dynamics of remote spin-entangled pairs in the expansion of strongly correlated fermions in an optical lattice

Stefan Kessler, Ian P. McCulloch, Florian Marquardt

We consider the nonequilibrium dynamics of an interacting spin-1/2 fermion gas in a one-dimensional optical lattice after switching off the confining potential. In particular, we study the creation and the time evolution of spatially separated, spin-entangled fermionic pairs. The time-dependent density-matrix renormalization group is used to simulate the time evolution and evaluate the two-site spin correlation functions, from which the concurrence is calculated. We find that the typical distance between entangled fermions depends crucially on the onsite interaction strength, and that a time-dependent modulation of the tunnelling amplitude can enhance the production of spin entanglement. Moreover, we discuss the prospects of experimentally observing these phenomena using spin-dependent single-site detection.

Gain-tunable optomechanical cooling in a laser cavity

Li Ge, Sanli Faez, Florian Marquardt, Hakan E. Tuereci

We study the optical cooling of the cavity mirror in an active laser cavity. We find that the optical damping rate is vanishingly small for an incoherently pumped laser above threshold. In the presence of an additional external coherent drive however, the optical damping rate can be enhanced substantially with respect to that of a passive cavity. We show that the strength of the incoherent pump provides the means to tune the optical damping rate and the steady state phonon number. The system is found to undergo a transition from the weak optomechanical coupling regime to the strong optomechanical coupling regime as the strength of the incoherent pump is varied.

Quantum Many-Body Dynamics in Optomechanical Arrays

Max Ludwig, Florian Marquardt

We study the nonlinear driven dissipative quantum dynamics of an array of optomechanical systems. At each site of such an array, a localized mechanical mode interacts with a laser-driven cavity mode via radiation pressure, and both photons and phonons can hop between neighboring sites. The competition between coherent interaction and dissipation gives rise to a rich phase diagram characterizing the optical and mechanical many-body states. For weak intercellular coupling, the mechanical motion at different sites is incoherent due to the influence of quantum noise. When increasing the coupling strength, however, we observe a transition towards a regime of phase-coherent mechanical oscillations. We employ a Gutzwiller ansatz as well as semiclassical Langevin equations on finite lattices, and we propose a realistic experimental implementation in optomechanical crystals.

Dynamics of levitated nanospheres: towards the strong coupling regime

T. S. Monteiro, J. Millen, G. A. T. Pender, Florian Marquardt, D. Chang, P. F. Barker

The use of levitated nanospheres represents a new paradigm for the optomechanical cooling of a small mechanical oscillator, with the prospect of realizing quantum oscillators with unprecedentedly high quality factors. We investigate the dynamics of this system, especially in the so-called self-trapping regime, where one or more optical fields simultaneously trap and cool the mechanical oscillator. The determining characteristic of this regime is that both the mechanical frequency omega(M) and single-photon optomechanical coupling strength parameters g are a function of the optical field intensities, in contrast to usual set-ups where omega(M) and g are constant for the given system. We also measure the characteristic transverse and axial trapping frequencies of different sized silica nanospheres in a simple optical standing wave potential, for spheres of radii r = 20-500 nm, illustrating a protocol for loading single nanospheres into a standing wave optical trap that would be formed by an optical cavity. We use these data to confirm the dependence of the effective optomechanical coupling strength on sphere radius for levitated nanospheres in an optical cavity and discuss the prospects for reaching regimes of strong light-matter coupling. Theoretical semiclassical and quantum displacement noise spectra show that for larger nanospheres with r greater than or similar to 100 nm a range of interesting and novel dynamical regimes can be accessed. These include simultaneous hybridization of the two optical modes with the mechanical modes and parameter regimes where the system is bistable. We show that here, in contrast to typical single-optical mode optomechanical systems, bistabilities are independent of intracavity intensity and can occur for very weak laser driving amplitudes.

Photonic Cavity Synchronization of Nanomechanical Oscillators

Mahmood Bagheri, Menno Poot, Linran Fan, Florian Marquardt, Hong X. Tang

Synchronization in oscillatory systems is a frequent natural phenomenon and is becoming an important concept in modern physics. Nanomechanical resonators are ideal systems for studying synchronization due to their controllable oscillation properties and engineerable nonlinearities. Here we demonstrate synchronization of two nanomechanical oscillators via a photonic resonator, enabling optomechanical synchronization between mechanically isolated nanomechanical resonators. Optical backaction gives rise to both reactive and dissipative coupling of the mechanical resonators, leading to coherent oscillation and mutual locking of resonators with dynamics beyond the widely accepted phase oscillator (Kuramoto) model. In addition to the phase difference between the oscillators, also their amplitudes are coupled, resulting in the emergence of sidebands around the synchronized carrier signal.