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.
Goos-Hanchen and Imbert-Fedorov shifts for bounded wavepackets of light
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.
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.
SCATTERING OF AN EXPONENTIAL PULSE BY A SINGLE ATOM
Markus Sondermann,
Gerd Leuchs
ROMANIAN REPORTS IN PHYSICS
65
(3)
638-645
(2013)
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
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
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.
Radially and azimuthally polarized nonparaxial Bessel beams made simple
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
JOURNAL OF THE EUROPEAN OPTICAL SOCIETY-RAPID PUBLICATIONS
8
13052
(2013)
| Journal
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.
Goos-Hanchen and Imbert-Fedorov beam shifts: an overview
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
Interferometric homogeneity test using adaptive frequency comb
illumination
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
Identical classical particles: Half fermions and half bosons
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
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
JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS
46
(9)
095502
(2013)
| Journal
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.
Goos-Hanchen and Imbert-Fedorov shifts from a quantum-mechanical
perspective
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
EUROPEAN PHYSICAL JOURNAL D
67
(3)
57
(2013)
| Journal
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
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.
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
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.
Corrections to the knife-edge based reconstruction scheme of tightly
focused light beams
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
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.
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.
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.
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.
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
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.
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.
Total absorption of light by a nanoparticle: an electromagnetic sink in
the optical regime
A. Sentenac,
P. C. Chaumet,
G. Leuchs
OPTICS LETTERS
38
(6)
818-820
(2013)
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
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
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.
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.
Nonclassical features of the polarization quasiprobability distribution
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.
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.
Causal signal transmission by quantum fields. VI: The Lorentz condition
and Maxwell's equations for fluctuations of the electromagnetic field
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.
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
JOURNAL OF THE EUROPEAN OPTICAL SOCIETY-RAPID PUBLICATIONS
8
13032
(2013)
| Journal
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.
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
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.
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