Aashish Clerk, Martin Houde, Florian Marquardt, Vittorio Peano
(2018)
Cavity optomechanics in a levitated helium drop
L. Childress, M. P. Schmidt, A. D. Kashkanova, C. D. Brown, G. I. Harris, Andrea Aiello, Florian Marquardt, J. G. E. Harris
PHYSICAL REVIEW A
96(6)
063842
(2017)

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We describe a proposal for a type of optomechanical system based on a drop of liquid helium that ismagnetically levitated in vacuum. In the proposed device, the drop would serve three roles: its optical whisperinggallery modes would provide the optical cavity, its surface vibrations would constitute the mechanical element, and evaporation of He atoms from its surface would provide continuous refrigeration. We analyze the feasibility of such a system in light of previous experimental demonstrations of its essential components: magnetic levitation of mmscale and cmscale drops of liquid He, evaporative cooling of He droplets in vacuum, and coupling to highquality optical whisperinggallery modes in a wide range of liquids. We find that the combination of these features could result in a device that approaches the singlephoton strongcoupling regime, due to the high optical quality factors attainable at low temperatures. Moreover, the system offers a unique opportunity to use optical techniques to study the motion of a superfluid that is freely levitating in vacuum (in the case of He4). Alternatively, for a normal fluid drop of He3, we propose to exploit the coupling between the drop's rotations and vibrations to perform quantum nondemolition measurements of angular momentum.
Multiparameter Quantum Metrology of Incoherent Point Sources: Towards Realistic Superresolution
J. Rehacek, Z. Hradil, B. Stoklasa, M. Paur, J. Grover, A. Krzic, L. L. SanchezSoto
Physical Review A
96(6)
062107
(2017)

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We establish the multiparameter quantum CramérRao bound for simultaneously estimating the centroid, the separation, and the relative intensities of two incoherent optical point sources using alinear imaging system. For equally bright sources, the CramérRao bound is independent of the source separation, which confirms that the Rayleigh resolution limit is just an artifact of the
conventional direct imaging and can be overcome with an adequate strategy. For the general case of unequally bright sources, the amount of information one can
gain about the separation falls to zero, but we show that there is always a quadratic improvement in an optimal detection in comparison with the intensity measurements. This advantage can be of utmost important in realistic scenarios, such as observational astronomy.
L lines, C points and Chern numbers: understanding band structure topology using polarization fields
Thomas Fösel, Vittorio Peano, Florian Marquardt
New Journal of Physics
19
115013
(2017)

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Topology has appeared in different physical contexts. The most prominent application is topologically protected edge transport in condensed matter physics. The Chern number, the topological invariant of gapped Bloch Hamiltonians, is an important quantity in this field. Another example of topology, in polarization physics, are polarization singularities, called L lines and C points. By establishing a connection between these two theories, we develop a novel technique to visualize and potentially measure the Chern number: it can be expressed either as the winding of the polarization azimuth along L lines in reciprocal space, or in terms of the handedness and the index of the C points. For mechanical systems, this is directly connected to the visible motion patterns.
Quantum metrology at the limit with extremal Majorana constellations
F. Bouchard, P. de la Hoz, G. Bjork, R. W. Boyd, M. Grassl, Z. Hradil, E. Karimi, A. B. Klimov, G. Leuchs, et al.
Quantum metrology allows for a tremendous boost in the accuracy of measurement of diverse physical parameters. The estimation of a rotation
constitutes a remarkable example of this quantumenhanced precision. The recently introduced Kings of Quantumness are especially germane for this task
when the rotation axis is unknown, as they have a sensitivity independent of that axis and they achieve a Heisenberglimit scaling. Here, we report the
experimental realization of these states by generating up to 21dimensional orbital angular momentum states of single photons, and confirm their high metrological abilities.
FibonacciLucas SICPOVMs
Markus Grassl, Andrew J. Scott
Journal of Mathematical Physics
58
122201
(2017)

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We present a conjectured family of SICPOVMs which have an additional
symmetry group whose size is growing with the dimension. The symmetry group is
related to Fibonacci numbers, while the dimension is related to Lucas numbers.
The conjecture is supported by exact solutions for dimensions
d=4,8,19,48,124,323, as well as a numerical solution for dimension d=844.
Kinetics of CrPV and HCV IRESmediated eukaryotic translation using singlemolecule fluorescence microscopy
Olivier Bugaud, Nathalie Barbier, Helene Chommy, Nicolas Fiszman, Antoine Le Gall, David Dulin, Matthieu Saguy, Nathalie Westbrook, Karen Perronet, et al.
Protein synthesis is a complex multistep process involving many factors that need to interact in a coordinated manner to properly translate the messenger RNA. As translating ribosomes cannot be synchronized over many elongation cycles, singlemolecule studies have been introduced to bring a deeper understanding of prokaryotic translation dynamics. Extending this approach to eukaryotic translation is very appealing, but initiation and specific labeling of the ribosomes are much more complicated. Here, we use a noncanonical translation initiation based on internal ribosome entry sites (IRES), and we monitor the passage of individual, unmodified mammalian ribosomes at specific fluorescent milestones along mRNA. We explore initiation by two types of IRES, the intergenic IRES of cricket paralysis virus (CrPV) and the hepatitis C (HCV) IRES, and show that they both strongly limit the rate of the first elongation steps compared to the following ones, suggesting that those first elongation cycles do not correspond to a canonical elongation. This new system opens the possibility of studying both IRESmediated initiation and elongation kinetics of eukaryotic translation and will undoubtedly be a valuable tool to investigate the role of translation machinery modifications in human diseases.
Signatures of Nucleotide Analog Incorporation by an RNADependent RNA
Polymerase Revealed Using HighThroughput Magnetic Tweezers
David Dulin, Jamie J. Arnold, Theo van Laar, HyungSuk Oh, Cheri Lee, Angela L. Perkins, Daniel A. Harki, Martin Depken, Craig E. Cameron, et al.
RNA viruses pose a threat to public health that is exacerbated by the dearth of antiviral therapeutics. The RNAdependent RNA polymerase (RdRp) holds promise as a broadspectrum, therapeutic target because of the conserved nature of the nucleotidesubstratebinding and catalytic sites. Conventional, quantitative, kinetic analysis of antiviral ribonucleotides monitors one or a few incorporation events. Here, we use a highthroughput magnetic tweezers platformto monitor the elongation dynamics of a prototypicalRdRpover thousands of nucleotideaddition cycles in the absence and presence of a suite of nucleotide analog inhibitors. We observe multiple RdRpRNA elongation complexes; only a subset of which are competent for analog utilization. Incorporation of a pyrazinecarboxamide nucleotide analog, T1106, leads to RdRp backtracking. This analysis reveals a mechanism of action for this antiviral ribonucleotide that is corroborated by cellular studies. We propose that induced backtracking represents a distinct mechanistic class of antiviral ribonucleotides.
Tracing the phase of focused broadband laser pulses
Dominik Hoff, Michael Krueger, Lothar Maisenbacher, A. M. Sayler, Gerhard G. Paulus, Peter Hommelhoff
Majorization uncertainty relations are generalized for an arbitrary mixed
quantum state $\rho$ of a finite size $N$. In particular, a lower bound for the
sum of two entropies characterizing probability distributions corresponding to
measurements with respect to arbitrary two orthogonal bases is derived in terms
of the spectrum of $\rho$ and the entries of a unitary matrix $U$ relating both
bases. The obtained results can also be formulated for two measurements
performed on a single subsystem of a bipartite system described by a pure
state, and consequently expressed as uncertainty relation for the sum of
conditional entropies.
General Linearized Theory of Quantum Fluctuations around Arbitrary Limit Cycles
Carlos NavarreteBenlloch, Talitha Weiss, Stefan Walter, Germán J. de Valcarcel
Physical Review Letters
119(13)
133601
(2017)

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PDF
The theory of Gaussian quantum fluctuations around classical steady states in nonlinear quantumoptical systems (also known as standard linearization) is a cornerstone for the analysis of such systems. Its simplicity, together with its accuracy far from critical points or situations where the nonlinearity reaches the strong coupling regime, has turned it into a widespread technique, being the first method of choice in most works on the subject. However, such a technique finds strong practical and conceptual complications when one tries to apply it to situations in which the classical longtime solution is time dependent, a most prominent example being spontaneous limitcycle formation. Here, we introduce a linearization scheme adapted to such situations, using the driven Van der Pol oscillator as a test bed for the method, which allows us to compare it with full numerical simulations. On a conceptual level, the scheme relies on the connection between the emergence of limit cycles and the spontaneous breaking of the symmetry under temporal translations. On the practical side, the method keeps the simplicity and linear scaling with the size of the problem (number of modes) characteristic of standard linearization, making it applicable to large (manybody) systems.
Dielectric laser acceleration of subrelativistic electrons by fewcycle laser pulses
M. Kozak, M. Foerster, J. McNeur, N. Schoenenberger, K. Leedle, H. Deng, J. S. Harris, R. L. Byer, P. Hommelhoff
NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION AACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT
865
8486
(2017)

Journal
In this paper we show the application of fewcycle infrared laser pulses for dielectric laser acceleration of electrons in the vicinity of a silicon nanostructure. An ultrashort pulse duration of 20 fs (3.3 optical cycles) allows achieving high peak fields of 2.8 GV/m without structural damage, leading to a peak acceleration gradient of G(p)=210 MeV/m for subrelativistic electrons (v=0.33c).
Cavity Antiresonance Spectroscopy of Dipole Coupled Subradiant Arrays
David Plankensteiner, Christian Sommer, Helmut Ritsch, Claudiu Genes
An array of N closely spaced dipole coupled quantum emitters exhibits superand subradiance with characteristic tailorable spatial radiation patterns. Optimizing the emitter geometry and distance with respect to the spatial profile of a near resonant optical cavity mode allows us to increase the ratio between light scattering into the cavity mode and free space emission by several orders of magnitude. This leads to distinct scaling of the collective coherent emitterfield coupling vs the free space decay as a function of the emitter number. In particular, for subradiant states, the effective cooperativity increases much faster than the typical linear proportional to N scaling for independent emitters. This extraordinary collective enhancement is manifested both in the amplitude and the phase profile of narrow collective antiresonances appearing at the cavity output port in transmission spectroscopy.
Unraveling beam selfhealing
Andrea Aiello, Girish S. Agarwal, Martin Paur, Bohumil Stoklasa, Zdenek Hradil, Jaroslav Rehacek, Pablo de la Hoz, Gerd Leuchs, Luis L. SanchezSoto
Optics Express
25(16)
1914719157
(2017)

Journal

PDF
We show that, contrary to popular belief, diffractionfree beams not only may reconstruct themselves after hitting an opaque obstacle but also, for example, Gaussian beams. We unravel the mathematics and the physics underlying the selfreconstruction mechanism and we provide for a novel definition for the minimum reconstruction distance beyond geometric optics, which is in principle applicable to any optical beam that admits an angular spectrum representation. Moreover, we propose to quantify the selfreconstruction ability of a beam via a newly established degree of selfhealing. This is defined via a comparison between the amplitudes, as opposite to intensities, of the original beam and the obstructed one. Such comparison is experimentally accomplished by tailoring an innovative experimental technique based upon ShackHartmann wave front reconstruction. We believe that these results can open new avenues in this field. (C) 2017 Optical Society of America
Efficient tomography with unknown detectors
L. Motka, M. Paur, J. Rehacek, Z. Hradil, L. L. SanchezSoto
We compare the two main techniques used for estimating the state of a
physical system from unknown measurements: standard detector tomography and
datapattern tomography. Adopting linear inversion as a fair benchmark, we show
that the difference between these two protocols can be traced back to the
nonexistence of the reverseorder law for pseudoinverses. We capitalize on this
fact to identify regimes where the datapattern approach outperforms the
standard one and vice versa. We corroborate these conclusions with numerical
simulations of relevant examples of quantum state tomography.
From KardarParisiZhang scaling to explosive desynchronization in arrays of limitcycle oscillators
Roland Lauter, Aditi Mitra, Florian Marquardt
Physical Review E
96(1)
012220
(2017)

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Phase oscillator lattices subject to noise are one of the most fundamental systems in nonequilibrium physics. We have discovered a dynamical transition which has a significant impact on the synchronization dynamics in such lattices, as it leads to an explosive increase of the phase diffusion rate by orders of magnitude. Our analysis is based on the widely applicable KuramotoSakaguchi model, with local couplings between oscillators. For onedimensional lattices, we observe the universal evolution of the phase spread that is suggested by a connection to the theory of surface growth, as described by the KardarParisiZhang (KPZ) model. Moreover, we are able to explain the dynamical transition both in one and two dimensions by connecting it to an apparent finitetime singularity in a related KPZ lattice model. Our findings have direct consequences for the frequency stability of coupled oscillator lattices.Phase oscillator lattices subject to noise are one of the most fundamental systems in nonequilibrium physics. We have discovered a dynamical transition which has a significant impact on the synchronization dynamics in such lattices, as it leads to an explosive increase of the phase diffusion rate by orders of magnitude. Our analysis is based on the widely applicable KuramotoSakaguchi model, with local couplings between oscillators. For onedimensional lattices, we observe the universal evolution of the phase spread that is suggested by a connection to the theory of surface growth, as described by the KardarParisiZhang (KPZ) model. Moreover, we are able to explain the dynamical transition both in one and two dimensions by connecting it to an apparent finitetime singularity in a related KPZ lattice model. Our findings have direct consequences for the frequency stability of coupled oscillator lattices.
Invariant Perfect Tensors
Youning Li, Muxin Han, Markus Grassl, Bei Zeng
New Journal of Physics
19
063029
(2017)

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Invariant tensors are states in the SU(2) tensor product representation that are invariant under the SU(2) action. They play an important role in the study of loop quantum gravity. On the other hand, perfect tensors are highly
entangled manybody quantum states with local density matrices maximally mixed. Recently, the notion of perfect tensors recently has attracted a lot of
attention in the fields of quantum information theory, condensed matter theory, and quantum gravity. In this work, we introduce the concept of an invariant perfect tensor (IPT), which is a $n$valent tensor that is both invariant and perfect. We discuss the existence and construction of IPT. For bivalent tensors, the invariant perfect tensor is the unique singlet state for each local dimension. The trivalent invariant perfect tensor also exists and is uniquely given by Wigner's 3j symbol. However, we show that, surprisingly, there does not exist fourvalent invariant perfect tensors for any dimension. On the contrary, when the dimension is large, almost all invariant tensors are perfect asymptotically, which is a consequence of the phenomenon of
concentration of measure for multipartite quantum states.
Probing the salt dependence of the torsional stiffness of DNA by multiplexed magnetic torque tweezers
Franziska Kriegel, Niklas Ermann, Ruaridh Forbes, David Dulin, Nynke H. Dekker, Jan Lipfert
Nucleic Acids Research
45(10)
59205929
(2017)

Journal
The mechanical properties of DNA fundamentally constrain and enable the storage and transmission of genetic information and its use in DNA nanotechnology. Many properties of DNA depend on the ionic environment due to its highly charged backbone. In particular, both theoretical analyses and direct singlemolecule experiments have shown its bending stiffness to depend on salt concentration. In contrast, the saltdependence of the twist stiffness of DNA is much less explored. Here, we employ optimized multiplexed magnetic torque tweezers to study the torsional stiffness of DNA under varying salt conditions as a function of stretching force. At low forces (< 3 pN), the effective torsional stiffness is similar to 10% smaller for high salt conditions (500 mM NaCl or 10 mM MgCl2) compared to lower salt concentrations (20 mM NaCl and 100 mM NaCl). These differences, however, can be accounted for by taking into account the known salt dependence of the bending stiffness. In addition, the measured highforce (6.5 pN) torsional stiffness values of C = 103 +/ 4 nm are identical, within experimental errors, for all tested salt concentration, suggesting that the intrinsic torsional stiffness of DNA does not depend on salt.
Towards optimal quantum tomography with unbalanced homodyning
Yong Siah Teo, Hyunseok Jeong, Luis L. SanchezSoto
Balanced homodyning, heterodyning and unbalanced homodyning are the three
wellknown sampling techniques used in quantum optics to characterize all
possible photonic sources in continuousvariable quantum information theory. We
show that for all quantum states and all observableparameter tomography
schemes, which includes the reconstructions of arbitrary operator moments and
phasespace quasidistributions, localized sampling with unbalanced homodyning
is always tomographically more powerful (gives more accurate estimators) than
delocalized sampling with heterodyning. The latter is recently known to often
give more accurate parameter reconstructions than conventional marginalized
sampling with balanced homodyning. This result also holds for realistic
photodetectors with subunit efficiency. With examples from first through
fourthmoment tomography, we demonstrate that unbalanced homodyning can
outperform balanced homodyning when heterodyning fails to do so. This new
benchmark takes us one step towards optimal continuousvariable tomography with
conventional photodetectors and minimal experimental components.
Synchronization of an optomechanical system to an external drive
Ehud Amitai, Niels Loerch, Andreas Nunnenkamp, Stefan Walter, Christoph Bruder
Physical Review A
95(5)
053858
(2017)

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PDF
Optomechanical systems driven by an effective bluedetuned laser can exhibit selfsustained oscillations of the mechanical oscillator. These selfoscillations are a prerequisite for the observation of synchronization. Here, we study the synchronization of the mechanical oscillations to an external reference drive. We study two cases of reference drives: (1) an additional laser applied to the optical cavity; (2) a mechanical drive applied directly to the mechanical oscillator. Starting from a master equation description, we derive a microscopic Adler equation for both cases, valid in the classical regime in which the quantum shot noise of the mechanical selfoscillator does not play a role. Furthermore, we numerically show that, in both cases, synchronization arises also in the quantum regime. The optomechanical system is therefore a good candidate for the study of quantum synchronization.
Focusing characteristics of a 4 pi parabolic mirror lightmatter interface
Lucas Alber, Martin Fischer, Marianne Bader, Klaus Mantel, Markus Sondermann, Gerd Leuchs
JOURNAL OF THE EUROPEAN OPTICAL SOCIETYRAPID PUBLICATIONS
13
14
(2017)

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PDF
Background: Focusing with a 4 pi parabolic mirror allows for concentrating light from nearly the complete solid angle, whereas focusing with a single microscope objective limits the angle cone used for focusing to half solid angle at maximum. Increasing the solid angle by using deep parabolic mirrors comes at the cost of adding more complexity to the mirror's fabrication process and might introduce errors that reduce the focusing quality.
Methods: To determine these errors, we experimentally examine the focusing properties of a 4p parabolic mirror that was produced by singlepoint diamond turning. The properties are characterized with a single Yb174(+) ion as a mobile point scatterer. The ion is trapped in a vacuum environment with a movable high optical access Paul trap.
Results: We demonstrate an effective focal spot size of 209 nm in lateral and 551 nm in axial direction. Such tight focusing allows us to build an efficient lightmatter interface.
Conclusion: Our findings agree with numerical simulations incorporating a finite ion temperature and interferometrically measured wavefront aberrations induced by the parabolic mirror. We point at further technological improvements and discuss the general scope of applications of a 4p parabolic mirror.
Quantumcoherent phase oscillations in synchronization
Talitha Weiss, Stefan Walter, Florian Marquardt
Physical Review A
95(4)
041802
(2017)

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Recently, several studies have investigated synchronization in quantummechanical limitcycle oscillators. However, the quantum nature of these systems remained partially hidden, since the dynamics of the oscillator's phase was overdamped and therefore incoherent. We show that there exist regimes of underdamped and even quantumcoherent phase motion, opening up new possibilities to study quantum synchronization dynamics. To this end, we investigate the Van der Pol oscillator (a paradigm for a selfoscillating system) synchronized to an external drive. We derive an effective quantum model which fully describes the regime of underdamped phase motion and additionally allows us to identify the quality of quantum coherence. Finally, we identify quantum limit cycles of the phase itself.
ManyParticle Dephasing after a Quench
Thomas Kiendl, Florian Marquardt
Physical Review Letters
118(13)
130601
(2017)

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PDF
After a quench in a quantum manybody system, expectation values tend to relax towards longtime averages. However, temporal fluctuations remain in the longtime limit, and it is crucial to study the suppression of these fluctuations with increasing system size. The particularly important case of nonintegrable models has been addressed so far only by numerics and conjectures based on analytical bounds. In this work, we are able to derive analytical predictions for the temporal fluctuations in a nonintegrable model (the transverse Ising chain with extra terms). Our results are based on identifying a dynamical regime of "manyparticle dephasing,"where quasiparticles do not yet relax but fluctuations are nonetheless suppressed exponentially by weak integrability breaking.
Pseudomagnetic fields for sound at the nanoscale
Christian Brendel, Vittorio Peano, Oskar J. Painter, Florian Marquardt
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
114(17)
E3390E3395

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PDF
There is a growing effort in creating chiral transport of sound waves. However, most approaches so far have been confined to the macroscopic scale. Here, we propose an approach suitable to the nanoscale that is based on pseudomagnetic fields. These pseudomagnetic fields for sound waves are the analogue of what electrons experience in strained graphene. In our proposal, they are created by simple geometrical modifications of an existing and experimentally proven phononic crystal design, the snowflake crystal. This platform is robust, scalable, and wellsuited for a variety of excitation and readout mechanisms, among them optomechanical approaches.
Coarse graining the phase space of N qubits
Olivia Di Matteo, Luis L. SanchezSoto, Gerd Leuchs, Markus Grassl
Physical Review A
95(2)
022340
(2017)

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PDF
We develop a systematic coarse graining procedure for systems of N qubits. We exploit the underlying geometrical structures of the associated discrete
phase space to produce a coarsegrained version with reduced effective size. Our coarsegrained spaces inherit key properties of the original ones. In
particular, our procedure naturally yields a subset of the original measurement operators, which can be used to construct a coarse discrete Wigner function. These operators also constitute a systematic choice of incomplete measurements for the tomographer wishing to probe an intractably large system.
Significant performance enhancement of InGaN/GaN nanorod LEDs with multilayer graphene transparent electrodes by alumina surface passivation
Michael Latzel, P. Buettner, George Sarau, Katja Höflich, Martin Heilmann, W. Chen, X. Wen, G. Conibeer, Silke Christiansen
Nanotextured surfaces provide an ideal platform for efficiently capturing and emitting light. However, the increased surface area in combination with surface defects induced by nanostructuring e.g. using reactive ion etching (RIE) negatively affects the device's active region and, thus, drastically decreases device performance. In this work, the influence of structural defects and surface states on the optical and electrical performance of InGaN/GaN nanorod (NR) light emitting diodes (LEDs) fabricated by topdown RIE of cplane GaN with InGaN quantum wells was investigated. After proper surface treatment a significantly improved device performance could be shown. Therefore, wet chemical removal of damaged material in KOH solution followed by atomic layer deposition of only 10 nm alumina as wide bandgap oxide for passivation were successfully applied. Raman spectroscopy revealed that the initially compressively strained InGaN/GaN LED layer stack turned into a virtually completely relaxed GaN and partially relaxed InGaN combination after RIE etching of NRs. Timecorrelated single photon counting provides evidence that both treatmentschemical etching and alumina depositionreduce the number of pathways for nonradiative recombination. Steadystate photoluminescence revealed that the luminescent performance of the NR LEDs is increased by about 50% after KOH and 80% after additional alumina passivation. Finally, complete NR LED devices with a suspended graphene contact were fabricated, for which the effectiveness of the alumina passivation was successfully demonstrated by electroluminescence measurements.
Cryogenic optical localization provides 3D protein structure data with Angstrom resolution
Siegfried Weisenburger, Daniel Boening, Benjamin Schomburg, Karin Giller, Stefan Becker, Christian Griesinger, Vahid Sandoghdar
We introduce Cryogenic Optical Localization in 3D (COLD), a method to localize multiple fluorescent sites within a single small protein with Angstrom resolution. We demonstrate COLD by determining the conformational state of the cytosolic PerARNTSim domain from the histidine kinase CitA of Geobacillus thermodenitnficans and resolving the four biotin sites of streptavidin. COLD provides quantitative 3D information about small to mediumsized biomolecules on the Angstrom scale and complements other techniques in structural biology.
High visibility in twocolor abovethreshold photoemission from tungsten nanotips in a coherent control scheme
Timo Paschen, Michael Förster, Michael Krüger, Christoph Lemell, Georg Wachter, Florian Libisch, Thomas Madlener, Joachim Burgdoerfer, Peter Hommelhoff
JOURNAL OF MODERN OPTICS
64(1011)
10541060
(2017)

Journal
In this article, we present coherent control of abovethreshold photoemission from a tungsten nanotip achieving nearly perfect modulation. Depending on the pulse delay between fundamental (1560nm) and second harmonic (780nm) pulses of a femtosecond fiber laser at the nanotip, electron emission is significantly enhanced or depressed during temporal overlap. Electron emission is studied as a function of pulse delay, optical nearfield intensities, DC bias field and final photoelectron energy. Under optimized conditions modulation amplitudes of the electron emission of 97.5% are achieved. Experimental observations are discussed in the framework of quantumpathway interference supported by local density of states simulations.
Optical gating and streaking of free electrons with suboptical cycle precision
M. Kozak, J. McNeur, K. J. Leedle, H. Deng, N. Schoenenberger, A. Ruehl, I. Hartl, J. S. Harris, R. L. Byer, et al.
The temporal resolution of ultrafast electron diffraction and microscopy experiments is currently limited by the available experimental techniques for the generation and characterization of electron bunches with single femtosecond or attosecond durations. Here, we present proof of principle experiments of an optical gating concept for free electrons via direct timedomain visualization of the suboptical cycle energy and transverse momentum structure imprinted on the electron beam. We demonstrate a temporal resolution of 1.2 +/ 0.3 fs. The scheme is based on the synchronous interaction between electrons and the nearfield mode of a dielectric nanograting excited by a femtosecond laser pulse with an optical period duration of 6.5 fs. The suboptical cycle resolution demonstrated here is promising for use in laserdriven streak cameras for attosecond temporal characterization of bunched particle beams as well as timeresolved experiments with freeelectron beams.
Small sets of complementary observables
M. Grassl, D. McNulty, L. Mišta, T. Paterek
Physical Review A
95(1)
012118
(2017)

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PDF
Two observables are called complementary if preparing a physical object in an eigenstate of one of them yields a completely random result in a measurement of
the other. We investigate small sets of complementary observables that cannot be extended by yet another complementary observable. We construct explicit
examples of the unextendible sets up to dimension $16$ and conjecture certain small sets to be unextendible in higher dimensions. Our constructions provide
three complementary measurements, only one observable away from the ultimate minimum of two observables in the set. Almost all of our examples in finite dimension allow to discriminate pure states from some mixed states, and shed light on the complex topology of the Bloch space of higherdimensional quantum systems.
Generalized nonreciprocity in an optomechanical circuit via synthetic magnetism and reservoir engineering
Kejie Fang, Jie Luo, Anja Metelmann, Matthew H. Matheny, Florian Marquardt, Aashish A. Clerk, Oskar Painter
Synthetic magnetism has been used to control charge neutral excitations for applications ranging from classical beam steering to quantum simulation. In optomechanics, radiationpressureinduced parametric coupling between optical (photon) and mechanical (phonon) excitations may be used to break timereversal symmetry, providing the prerequisite for synthetic magnetism. Here we design and fabricate a silicon optomechanical circuit with both optical and mechanical connectivity between two optomechanical cavities. Driving the two cavities with phasecorrelated laser light results in a synthetic magnetic flux, which, in combination with dissipative coupling to the mechanical bath, leads to nonreciprocal transport of photons with 35 dB of isolation. Additionally, optical pumping with bluedetuned light manifests as a particle nonconserving interaction between photons and phonons, resulting in directional optical amplification of 12 dB in the isolator throughdirection. These results suggest the possibility of using optomechanical circuits to create a more general class of nonreciprocal optical devices, and further, to enable new topological phases for both light and sound on a microchip.
Shifting the phase of a coherent beam with a Yb174(+) ion: influence of the scattering cross section
Martin Fischer, Bharath Srivathsan, Lucas Alber, Markus Weber, Markus Sondermann, Gerd Leuchs
APPLIED PHYSICS BLASERS AND OPTICS
123(1)
48
(2017)

Journal

PDF
We discuss and measure the phase shift imposed onto a radially polarized light beam when focusing it onto an Yb174(+) ion. In the derivation of the expected phase shifts, we include the properties of the involved atomic levels. Furthermore, we emphasize the importance of the scattering cross section and its relation to the efficiency for coupling the focused light to an atom. The phase shifts found in the experiment are compatible with the expected ones when accounting for known deficiencies of the focusing optics and the motion of the trapped ion at the Doppler limit of laser cooling (Hensch and Schawlow in Opt Commun 13:6869,1975).
Anderson localization of composite excitations in disordered optomechanical arrays
Thales Figueiredo Roque, Vittorio Peano, Oleg M. Yevtushenko, Florian Marquardt
New Journal of Physics
19
013006
(2017)

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PDF
Optomechanical (OMA) arrays are a promising future platform for studies of transport, manybody dynamics, quantum control and topological effects in systems of coupled photon and phonon modes. We introduce disordered OMA arrays, focusing on features of Anderson localization of hybrid photonphonon excitations. It turns out that these represent a unique disordered system, where basic parameters can be easily controlled by varying the frequency and the amplitude of an external laser field. We show that the twospecies setting leads to a nontrivial frequency dependence of the localization length for intermediate laser intensities. This could serve as a convincing evidence of localization in a nonequilibrium dissipative situation.
Roadmap on structured light
Halina RubinszteinDunlop, Andrew Forbes, M. V. Berry, M. R. Dennis, David L. Andrews, Masud Mansuripur, Cornelia Denz, Christina Alpmann, Peter Banzer, et al.
Structured light refers to the generation and application of custom light fields. As the tools and technology to create and detect structured light have evolved, steadily the applications have begun to emerge. This roadmap touches on the key fields within structured light from the perspective of experts in those areas, providing insight into the current state and the challenges their respective fields face. Collectively the roadmap outlines the venerable nature of structured light research and the exciting prospects for the future that are yet to be realized.
Lightmatter interactions in multielement resonators
Claudiu Genes, Aurelien Dantan
JOURNAL OF PHYSICS BATOMIC MOLECULAR AND OPTICAL PHYSICS
50(10)
105502
(2017)

Journal
We investigate lightmatter interactions in multielement optical resonators and provide a roadmap for the identification of structural resonances and the description of the interaction of single extended cavity modes with quantum emitters or mechanical resonators. Using a first principle approach based on the transfer matrix formalism we analyze, both numerically and analytically, the static and dynamical properties of threeand fourmirror cavities. We investigate in particular conditions under which the confinement of the field in specific subcavities allows for enhanced lightmatter interactions in the context of cavity quantum electrodynamics and cavity optomechanics.
Optimal measurements for resolution beyond the Rayleigh limit
J. Rehacek, M. Paur, B. Stoklasa, Z. Hradil, L. L. SanchezSoto
We establish the conditions to attain the ultimate resolution predicted by quantum estimation theory for the case of two incoherent point sources using a linear imaging system. The solution is closely related to the spatial symmetries of the detection scheme. In particular, for real symmetric point spread functions, any complete set of projections with definite parity achieves the goal. (C) 2017 Optical Society of America
Invariant tensors are states in the SU(2) tensor product representation that are invariant under SU(2) action. They play an important role in the study of loop quantum gravity. On the other hand, perfect tensors are highly entangled manybody quantum states with local density matrices maximally mixed. Recently, the notion of perfect tensors has attracted a lot of attention in the fields of quantum information theory, condensed matter theory, and quantum gravity. In this work, we introduce the concept of an invariant perfect tensor (IPT), which is an nvalent tensor that is both invariant and perfect. We discuss the existence and construction of IPTs. For bivalent tensors, the IPT is the unique singlet state for each local dimension. The trivalent IPT also exists and is uniquely given by Wigner's 3j symbol. However, we show that, surprisingly, 4valent IPTs do not exist for any identical local dimension d. On the contrary, when the dimension is large, almost all invariant tensors are asymptotically perfect, which is a consequence of the phenomenon of the concentration of measure for multipartite quantum states.
Freespace propagation of highdimensional structured optical fields in
an urban environment
Martin P. J. Lavery, Christian Peuntinger, Kevin Guenthner, Peter Banzer, Dominique Elser, Robert W. Boyd, Miles J. Padgett, Christoph Marquardt, Gerd Leuchs
Spatially structured optical fields have been used to enhance the functionality of a wide variety of systems that use light for sensing or information transfer. As higherdimensional modes become a solution of choice in optical systems, it is important to develop channel models that suitably predict the effect of atmospheric turbulence on these modes. We investigate the propagation of a set of orthogonal spatial modes across a freespace channel between two buildings separated by 1.6 km. Given the circular geometry of a common optical lens, the orthogonal mode set we choose to implement is that described by the LaguerreGaussian (LG) field equations. Our study focuses on the preservation of phase purity, which is vital for spatial multiplexing and any system requiring full quantumstate tomography. We present experimental data for the modal degradation in a real urban environment and draw a comparison to recognized theoretical predictions of the link. Our findings indicate that adaptations to channel models are required to simulate the effects of atmospheric turbulence placed on highdimensional structured modes that propagate over a long distance. Our study indicates that with mitigation of vortex splitting, potentially through precorrection techniques, one could overcome the challenges in a real pointtopoint freespace channel in an urban environment.
Optimally cloned binary coherent states
C. R. Mueller, G. Leuchs, Ch. Marquardt, U. L. Andersen
Binary coherent state alphabets can be represented in a twodimensional Hilbert space. We capitalize this formal connection between the otherwise distinct domains of qubits and continuous variable states to map binary phaseshift keyed coherent states onto the Bloch sphere and to derive their quantumoptimal clones. We analyze the Wigner function and the cumulants of the clones, and we conclude that optimal cloning of binary coherent states requires a nonlinearity above second order. We propose several practical and nearoptimal cloning schemes and compare their cloning fidelity to the optimal cloner.
Some results on the structure of constacyclic codes and new linear codes over GF(7) from quasitwisted codes
Nuh Aydin, Nicholas Connolly, Markus Grassl
ADVANCES IN MATHEMATICS OF COMMUNICATIONS
11(1)
245258
(2017)

Journal
One of the most important and challenging problems in coding theory is to construct codes with good parameters. There are various methods to construct codes with the best possible parameters. A promising and fruitful approach has been to focus on the class of quasitwisted (QT) codes which includes constacyclic codes as a special case. This class of codes is known to contain many codes with good parameters. Although constacyclic codes and QT codes have been the subject of numerous studies and computer searches over the last few decades, we have been able to discover a new fundamental result about the structure of constacyclic codes which was instrumental in our comprehensive search method for new QT codes over GF(7). We have been able to find 41 QT codes with better parameters than the previously best known linear codes. Furthermore, we derived a number of additional new codes via Construction X as well as standard constructions, such as shortening and puncturing.
New selfdual additive F_4codes constructed from circulant graphs
In order to construct quantum [[n, 0, d]] codes for (n, d) = (56, 15), (57, 15), (58, 16), (63, 16), (67, 17), (70, 18), (71, 18), (79, 19), (83, 20), (87, 20), (89, 21), (95, 20), we construct selfdual additive F4codes of length n and minimum weight d from circulant graphs. The quantum codes with these parameters are constructed for the first time. (C) 2016 Elsevier B.V. All rights reserved.
Efficient Nitrogen Doping of SingleLayer Graphene Accompanied by Negligible Defect Generation for Integration into Hybrid Semiconductor Heterostructures
George Sarau, Martin Heilmann, Muhammad Bashouti, Michael Latzel, Christian Tessarek, Silke Christiansen
doping enables applicationspecific tailoring of graphene properties, it can also produce high defect densities that degrade the beneficial features. In this work, we report efficient nitrogen doping of similar to 11 atom % without virtually inducing new structural defects in the initial, largearea, low defect, and transferred singlelayer graphene. To shed light on this remarkable highdoping Iowdisorder relationship, a unique experimental strategy consisting of analyzing the changes in doping, strain) and defect density after each important step during :the doping procedure was employed. Complementary microRaman mapping, Xray photoelectron spectroscopy, and optical microscopy revealed that effective cleaning of the graphene surface assists efficient nitrogen incorporation accompanied by mild compressive strain resulting in negligible defect formation in the doped graphene lattice. These original results are achieved by separating the growth of graphene from its doping. Moreover, the high doping level occurred simultaneously with the epitaxial growth of nGaN micro and nanorods On top of graphene, leading to the flow of higher currents through the graphene/nGaN rod interface. Our approach can be extended toward integrating graphene into other technologically relevant hybrid semiconductor heterostructures and obtaining an ohmic contact at their interfaces by adjusting the doping level in graphene.
Optical gating and streaking of free electrons with suboptical cycle
precision
M. Kozak, J. McNeur, K. J. Leedle, H. Deng, N. Schoenenberger, A. Ruehl, I. Hartl, J. S. Harris, R. L. Byer, et al.
The temporal resolution of ultrafast electron diffraction and microscopy experiments is currently limited by the available experimental techniques for the generation and characterization of electron bunches with single femtosecond or attosecond durations. Here, we present proof of principle experiments of an optical gating concept for free electrons via direct timedomain visualization of the suboptical cycle energy and transverse momentum structure imprinted on the electron beam. We demonstrate a temporal resolution of 1.2 +/ 0.3 fs. The scheme is based on the synchronous interaction between electrons and the nearfield mode of a dielectric nanograting excited by a femtosecond laser pulse with an optical period duration of 6.5 fs. The suboptical cycle resolution demonstrated here is promising for use in laserdriven streak cameras for attosecond temporal characterization of bunched particle beams as well as timeresolved experiments with freeelectron beams.
Plasmonic gold helices for the visible range fabricated by oxygen plasma purification of electron beam induced deposits
Caspar Haverkamp, Katja Hoeflich, Sara Jaeckle, Anna Manzoni, Silke Christiansen
Electron beam induced deposition (EBID) currently provides the only direct writing technique for truly threedimensional nanostructures with geometrical features below 50 nm. Unfortunately, the depositions from metalorganic precursors suffer from a substantial carbon content. This hinders many applications, especially in plasmonics where the metallic nature of the geometric surfaces is mandatory. To overcome this problem a postdeposition treatment with oxygen plasma at room temperature was investigated for the purification of gold containing EBID structures. Upon plasma treatment, the structures experience a shrinkage in diameter of about 18 nm but entirely keep their initial shape. The proposed purification step results in a coreshell structure with the core consisting of mainly unaffected EBID material and a gold shell of about 20 nm in thickness. These purified structures are plasmonically active in the visible wavelength range as shown by dark field optical microscopy on helical nanostructures. Most notably, electromagnetic modeling of the corresponding scattering spectra verified that the thickness and quality of the resulting gold shell ensures an optical response equal to that of pure gold nanostructures.
Linear and angular momenta in tightly focused vortex segmented beams of light
Martin Neugebauer, Andrea Aiello, Peter Banzer
CHINESE OPTICS LETTERS
15(3)
030003
(2017)

Journal

PDF
We investigate the linear momentum density of light, which can be decomposed into spin and orbital parts, in the complex threedimensional field distributions of tightly focused vortex segmented beams. The chosen angular spectrum exhibits two spatially separated vortices of opposite charge and orthogonal circular polarization to generate phase vortices in a meridional plane of observation. In the vicinity of those vortices, regions of negative orbital linear momentum occur. Besides these phase vortices, the occurrence of transverse orbital angular momentum manifests in a vortex chargedependent relative shift of the energy density and linear momentum density.
Quantumlimited measurements of optical signals from a geostationary
satellite
Kevin Guenthner, Imran Khan, Dominique Elser, Birgit Stiller, Oemer Bayraktar, Christian R. Mueller, Karen Saucke, Daniel Troendle, Frank Heine, et al.
The measurement of quantum signals that travel through long distances is fundamentally and technologically interesting. We present quantumlimited coherent measurements of optical signals that are sent from a satellite in geostationary Earth orbit to an optical ground station. We bound the excess noise that the quantum states could have acquired after having propagated 38,600 km through Earth's gravitational potential, as well as its turbulent atmosphere. Our results indicate that quantum communication is feasible, in principle, in such a scenario, highlighting the possibility of a global quantum key distribution network for secure communication. (C) 2017 Optical Society of America
Enhanced Control of Transient Raman Scattering Using Buffered Hydrogen in HollowCore Photonic Crystal Fibers
P. Hosseini, D. Novoa, A. Abdolvand, P. St. J. Russell
Many reports on stimulated Raman scattering in mixtures of Ramanactive and noble gases indicate that the addition of a dispersive buffer gas increases the phase mismatch to higherorder Stokes and antiStokes sidebands, resulting in a preferential conversion to the first few Stokes lines, accompanied by a significant reduction in the Raman gain due to collisions with gas molecules. Here we report that, provided the dispersion can be precisely controlled, the effective Raman gain in a gasfilled hollowcore photonic crystal fiber can actually be significantly enhanced when a buffer gas is added. This counterintuitive behavior occurs when the nonlinear coupling between the interacting fields is strong and can result in a performance similar to that of a pure Ramanactive gas, but at a much lower total gas pressure, allowing competing effects such as Raman backscattering to be suppressed. We report high modal purity in all the emitted sidebands, along with antiStokes conversion efficiencies as high as 5% in the visible and 2% in the ultraviolet. This new class of gasbased waveguide device, which allows the nonlinear optical response to be beneficially pressuretuned by the addition of buffer gases, may find important applications in laser science and spectroscopy.
Universality of Coherent Raman Gain Suppression in GasFilled BroadbandGuiding Photonic Crystal Fibers
Pooria Hosseini, M. K. Mridha, D. Novoa, A. Abdolvand, P. St. J. Russell
As shown in the early 1960s, the gain in stimulated Raman scattering (SRS) is drastically suppressed when the rate of creation of phonons (via a pumptoStokes conversion) is exactly balanced by the rate of phonon annihilation (via a pumptoantiStokes conversion). This occurs when the phonon coherence wavessynchronized vibrations of a large population of moleculeshave identical propagation constants for both processes; i. e., they are phasevelocity matched. As recently demonstrated, hydrogenfilled photonic crystal fiber pumped in the vicinity of its zerodispersion wavelength provides an ideal system for observing this effect. Here we report that Raman gain suppression is actually a universal feature of SRS in gasfilled hollowcore fibers and that it can strongly impair SRS even when the phase mismatch is high, particularly at high pump powers when it is normally assumed that nonlinear processes become more (not less) efficient. This counterintuitive result means that intermodal stimulated Raman scattering (for example, between LP01 and LP11 core modes) begins to dominate at high power levels. The results reported have important implications for fiberbased Raman shifters, amplifiers, or frequency combs, especially for operation in the ultraviolet, where the Raman gain is much higher.
Experimental demonstration of a predictable single photon source with
variable photon flux
Aigar Vaigu, Geiland Porrovecchio, XiaoLiu Chu, Sarah Lindner, Marek Smid, Albert Manninen, Christoph Becher, Vahid Sandoghdar, Stephan Gotzinger, et al.
We present a predictable singlephoton source (SPS) based on a silicon vacancy centre in nanodiamond which is optically excited by a pulsed laser. At an excitation rate of 70 MHz the source delivers a photon flux large enough to be measured by a low optical flux detector (LOFD). The directly measured photon flux constitutes an absolute reference. By changing the repetition rate of the pulsed laser, we are able to change the photon flux of our SPS in a controllable way which in turn can act as a reference. The advantage of our method is that it does not require precise knowledge of the source efficiency, but the source is calibrated by the LOFD and can be used for detector responsivity characterizations at the fewphoton level.
Generation of spectral clusters in a mixture of noble and Ramanactive
gases (vol 41, pg 5543, 2016)
Pooria Hosseini, Amir Abdolvand, Philip St. J. Russell
Monitoring the kinetics and conformational dynamics of single enzymes is crucial to better understand their biological functions because these motions and structural dynamics are usually unsynchronized among the molecules. However, detecting the enzymereactant interactions and associated conformational changes of the enzyme on a singlemolecule basis remains as a challenge to established optical techniques because of the commonly required labeling of the reactants or the enzyme itself. The labeling process is usually nontrivial, and the labels themselves might skew the physical properties of the enzyme. We demonstrate an optical, labelfree method capable of observing enzymatic interactions and associated conformational changes on a singlemolecule level. We monitor polymerase/DNA interactions via the strong nearfield enhancement provided by plasmonic nanorods resonantly coupled to whispering gallery modes in microcavities. Specifically, we use two different recognition schemes: one in which the kinetics of polymerase/DNA interactions are probed in the vicinity of DNAfunctionalized nanorods, and the other in which these interactions are probed via the magnitude of conformational changes in the polymerase molecules immobilized on nanorods. In both approaches, we find that low and high polymerase activities can be clearly discerned through their characteristic signal amplitude and signal length distributions. Furthermore, the thermodynamic study of the monitored interactions suggests the occurrence of DNA polymerization. This work constitutes a proofofconcept study of enzymatic activities using plasmonically enhanced microcavities and establishes an alternative and labelfree method capable of investigating structural changes in single molecules.
Temporal and spectral properties of quantum light
B. Stiller, U. Seyfarth, G. Leuchs, C. Fabre, V. Sandoghdar, N. Treps, L.F. Cugliandolo
Quantum Optics and Nanophotonics
169227
(2017)

Book Chapter

PDF
Improving the phase supersensitivity of squeezingassisted
interferometers by squeeze factor unbalancing
The sensitivity properties of an SU(1,1) interferometer made of two cascaded parametric amplifiers, as well as of an ordinary SU(2) interferometer preceded by a squeezer and followed by an antisqueezer, are theoretically investigated. Several possible experimental configurations are considered, such as the absence or presence of a seed beam, direct or homodyne detection scheme. In all cases we formulate the optimal conditions to achieve phase supersensitivity, meaning a sensitivity overcoming the shotnoise limit. Weshow that for a given gain of the first parametric amplifier, unbalancing the interferometer by increasing the gain of the second amplifier improves the interferometer properties. In particular, a broader supersensitivity phase range and a better overall sensitivity can be achieved by gain unbalancing.
Experimental detection of entanglement polytopes via local filters
YuanYuan Zhao, Markus Grassl, Bei Zeng, GuoYong Xiang, Chao Zhang, ChuanFeng Li, GuangCan Guo
Quantum entanglement, resulting in correlations between subsystems that are stronger than any possible classical correlation, is one of the mysteries of quantum mechanics. Entanglement cannot be increased by any local operation, and for a sufficiently large manybody quantum system there exist infinitely many different entanglement classes, i. e., states that are not related by stochastic local operations and classical communications. On the other hand, the method of entanglement polytopes results in finitely many coarsegrained types of entanglement that can be detected by only measuring singleparticle spectra. We find, however, that with high probability the local spectra lie in more than one polytope, hence providing only partial information about the entanglement type. To overcome this problem, we propose to additionally use socalled local filters, which are nonunitary local operations. We experimentally demonstrate the detection of entanglement polytopes in a fourqubit system. Using local filters we can distinguish the entanglement type of states with the same single particle spectra, but which belong to different polytopes.
We introduce a novel design of antiresonant fibers with negativecurvature square cores to be employed in 1.55 and 2.94 mu m transmission bands. The fibers have low losses and singlemode operation via optimizing the negative curvature of the guiding walls. The first proposed fiber shows a broadband transmission window spanning 0.91.7 mu m, with losses of 0.025 and 0.056 dB/m at 1.064 and 1.55 mu m, respectively. The second proposed fiber has approximately a 0.023 dB/m guiding loss at 2.94 mu m with a small crosssectional area, useful for laser micromachining applications. (C) 2017 Optical Society of America
Discrete phasespace structures and Wigner functions for N qubits
C. Munoz, A. B. Klimov, L. SanchezSoto
QUANTUM INFORMATION PROCESSING
16(6)
UNSP 158
(2017)

Journal
We further elaborate on a phasespace picture for a system of N qubits and explore the structures compatible with the notion of unbiasedness. These consist of bundles of discrete curves satisfying certain additional properties and different entanglement properties. We discuss the construction of discrete covariant Wigner functions for these bundles and provide several illuminating examples.
Interaction Between Dirac Solitons and JackiwRebbi States in Binary Waveguide Arrays
Truong X. Tran, Dung C. Duong, Fabio Biancalana
JOURNAL OF LIGHTWAVE TECHNOLOGY
35(23)
50925097
(2017)

Journal
We systematically study different scenarios of collision between Dirac solitons and JackiwRebbi (JR) states, which have been found recently in a system consisting of two interfaced binary waveguide arrays with opposite propagation mismatches. This collision has the resonance features for the reflected and transmitted signals. The trapping effect of Dirac solitons between two JRstates is analyzed.
PolarizationSelective OutCoupling of WhisperingGallery Modes
Florian Sedlmeir, Matthew R. Foreman, Ulrich Vogl, Richard Zeltner, Gerhard Schunk, Dmitry V. Strekalov, Christoph Marquardt, Gerd Leuchs, Harald G. L. Schwefel
Whisperinggallery mode (WGM) resonators are an important platform for linear, nonlinear, and quantum optical experiments. In such experiments, independent control of incoupling and outcoupling rates to different modes can lead to higher conversion efficiencies and greater flexibility in the generation of nonclassical states based on parametric downconversion. In this work, we introduce a scheme that enables selective outcoupling of WGMs belonging to a specific polarization family, while the orthogonally polarized modes remain largely unperturbed. Our technique utilizes material birefringence in both the resonator and the coupler such that a negative (positive) birefringence allows for polarizationselective coupling to TE (TM) WGMs. We formulate a refined coupling condition suitable for describing the case where the refractive indices of the resonator and the coupler are almost the same, from which we derive a criterion for polarizationselective coupling. Finally, we experimentally demonstrate our proposed method using a lithium niobate disk resonator coupled to a lithium niobate prism, where we show a 22dB suppression of coupling to TM modes relative to TE modes.
Hybrid photoniccrystal fiber
Christos Markos, John C. Travers, Amir Abdolvand, Benjamin J. Eggleton, Ole Bang
REVIEWS OF MODERN PHYSICS
89(4)
045003
(2017)

Journal
This article offers an extensive survey of results obtained using hybrid photoniccrystal fibers (PCFs) which constitute one of the most active research fields in contemporary fiber optics. The ability to integrate novel and functional materials in solidand hollowcore PCFs through various postprocessing methods has enabled new directions toward understanding fundamental linear and nonlinear phenomena as well as novel application aspects, within the fields of optoelectronics, material and laser science, remote sensing, and spectroscopy. Here the recent progress in the field of hybrid PCFs is reviewed from scientific and technological perspectives, focusing on how different fluids, solids, and gases can significantly extend the functionality of PCFs. The first part of this review discusses the efforts to develop tunable linear and nonlinear fiberoptic devices using PCFs infiltrated with various liquids, glasses, semiconductors, and metals. The second part concentrates on recent and stateoftheart advances in the field of gasfilled hollowcore PCFs. Extreme ultrafast gasbased nonlinear optics toward light generation in the extreme wavelength regions of vacuum ultraviolet, pulse propagation, and compression dynamics in both atomic and molecular gases, and novel solitonplasma interactions are reviewed. A discussion of future prospects and directions is also included.
Helically twisted photonic crystal fibres
P. St. J. Russell, Ramin Beravat, G. K. L. Wong
PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY AMATHEMATICAL PHYSICAL
AND ENGINEERING SCIENCES
375(2087)
20150440
(2017)

Journal
Recent theoretical and experimental work on helically twisted photonic crystal fibres (PCFs) is reviewed. Helical Bloch theory is introduced, including a new formalism based on the tightbinding approximation. It is used to explore and explain a variety of unusual effects that appear in a range of different twisted PCFs, including fibres with a single core and fibres with N cores arranged in a ring around the fibre axis. We discuss a new kind of birefringence that causes the propagation constants of leftand rightspinning optical vortices to be nondegenerate for the same order of orbital angular momentum (OAM). Topological effects, arising from the twisted periodic 'space', cause light to spiral around the fibre axis, with fascinating consequences, including the appearance of dips in the transmission spectrum and low loss guidance in coreless PCF. Discussing twisted fibres with a single offaxis core, we report that optical activity in a PCF is opposite in sign to that seen in a stepindex fibre. Fabrication techniques are briefly described and emerging applications reviewed. The analytical results of helical Bloch theory are verified by an extensive series of 'numerical experiments' based on finiteelement solutions of Maxwell's equations in a helicoidal frame.
This article is part of the themed issue 'Optical orbital angular momentum'.
Fundamental precision limit of a MachZehnder interferometric sensor
when one of the inputs is the vacuum
Masahiro Takeoka, Kaushik P. Seshadreesan, Chenglong You, Shuro Izumi, Jonathan P. Dowling
In the lore of quantum metrology, one often hears (or reads) the following nogo theorem: If you put a vacuum into one input port of a balanced MachZehnder interferometer, then no matter what you put into the other input port, and nomatter what your detection scheme, the sensitivity can never be better than the shotnoise limit (SNL). Often the proof of this theorem is cited to be inC. Caves, Phys. Rev. D23, 1693 (1981), but upon further inspection, no such claim is made there. QuantumFisherinformationbased arguments suggestive of this nogo theorem appear elsewhere in the literature, but are not stated in their full generality. Here we thoroughly explore this nogo theorem and give a rigorous statement: the nogo theorem holds whenever the unknown phase shift is split between both of the arms of the interferometer, but remarkably does not hold when only one arm has the unknown phase shift. In the latter scenario, we provide an explicit measurement strategy that beats the SNL. We also point out that these two scenarios are physically different and correspond to different types of sensing applications.
Freespace quantum links under diverse weather conditions
D. Vasylyev, A. A. Semenov, W. Vogel, K. Guenthner, A. Thurn, O. Bayraktar, Ch. Marquardt
Freespace optical communication links are promising channels for establishing secure quantum communication. Here we study the transmission of nonclassical light through a turbulent atmospheric link under diverse weather conditions, including rain or haze. To include these effects, the theory of light transmission through atmospheric links in the ellipticbeam approximation presented by Vasylyev et al. [D. Vasylyev et al., Phys. Rev. Lett. 117, 090501 (2016)] is further generalized. It is demonstrated, with good agreement between theory and experiment, that lowintensity rain merely contributes additional deterministic losses, whereas haze also introduces additional beam deformations of the transmitted light. Based on these results, we study theoretically the transmission of quadrature squeezing and Gaussian entanglement under these weather conditions.
Characterization and shaping of the timefrequency Schmidt mode spectrum
of bright twin beams generated in gasfilled hollowcore photonic
crystal fibers
M. A. Finger, N. Y. Joly, P. St. J. Russell, M. V. Chekhova
We vary the timefrequency mode structure of ultrafast pulsepumped modulational instability (MI) twin beams in an argonfilled hollowcore kagomestyle photonic crystal fiber by adjusting the pressure, pump pulse chirp, fiber length, and parametric gain. Compared to solidcore systems, the pressuredependent dispersion landscape brings increased flexibility to the tailoring of frequency correlations, and we demonstrate that the pump pulse chirp can be used to tune the joint spectrum of femtosecondpumped.(3) sources. We also characterize the resulting mode content, not only by measuring the multimode secondorder correlation function g((2)), but also by directly reconstructing the shapes and weights of timefrequency Schmidt (TFS) modes. We show that the number of modes directly influences the shottoshot pulseenergy and spectralshape fluctuations in MI. Using this approach we control and monitor the number of TFS modes within the range from 1.3 to 4 using only a single fiber.
Rapid screening of photoactivatable metallodrugs: photonic crystal fibre
microflow reactor coupled to ESI mass spectrometry
Ruth J. McQuitty, Sarah Unterkofler, Tijmen G. Euser, Philip St J. Russell, Peter J. Sadler
We explore the efficacy of a hyphenated photonic crystal fibre microflow reactorhighresolution mass spectrometer system as a method for screening the activity of potential new photoactivatable drugs. The use of light to activate drugs is an area of current development as it offers the possibility of reduced side effects due to improved spatial and temporal targeting and novel mechanisms of anticancer activity. The dinuclear ruthenium complex [{(eta(6)indan) RuCl}(2)(mu2,3dpp)](PF6)(2), previously studied by Magennis et al. (Inorg. Chem., 2007, 46, 5059) is used as a model drug to compare the system to standard irradiation techniques. The photodecomposition pathways using blue light radiation are the same for PCF and conventional cuvette methods. Reactions in the presence of small biomolecules 50guanosine monophosphate (5'GMP), 5'adenosine monophosphate (5'AMP), Lcysteine (LCys) and glutathione (gammaLglutamylLcysteinylglycine, GSH) were studied. The complex was found to bind to nucleobases in the dark and this binding increased upon irradiation with 488 nm light, forming the adducts [(eta(6)indan) Ru2(mu2,3dpp) + 5'GMP](2+) and [(eta(6)indan) Ru + (5'AMP)]+. These findings are consistent with studies using conventional methods. The dinuclear complex also binds strongly to GSH after irradiation, a possible explanation for its lack of potency in cell line testing. The use of the PCFMS system dramatically reduced the sample volume required and reduced the irradiation time by four orders of magnitude from 14 hours to 12 seconds. However, the reduced sample volume also results in a reduced MS signal intensity. The dead time of the combined system is 15 min, limited by the intrinsic dead volume of the HRMS.
Experimental demonstration of negativevalued polarization
quasiprobability distribution
Polarization quasiprobability distribution defined in the Stokes space shares many important properties with the Wigner function for position and momentum. Most notably, they both give correct onedimensional marginal probability distributions and therefore represent the natural choice for the probability distributions in classical hiddenvariable models. In this context, negativity of the Wigner function is considered as proof of nonclassicality for a quantum state. On the contrary, the polarization quasiprobability distribution demonstrates negativity for all quantum states. This feature comes from the discrete nature of Stokes variables; however, it was not observed in previous experiments, because they were performed with photonnumber averaging detectors. Here we reconstruct the polarization quasiprobability distribution of a coherent state with photonnumber resolving detectors, which allows us to directly observe for the first time its negativity. Furthermore we derive a theoretical polarization quasiprobability distribution for any linearly polarized quantum state.
Plasmon coherence determination by nanoscattering
Yahong Chen, Andreas Norrman, Sergey A. Ponomarenko, Ari T. Friberg
We present a simple and robust protocol to recover the secondorder field correlations of polychromatic, statistically stationary surface plasmon polaritons (SPPs) from a spectrum measurement in the far zone of a dipolar nanoscatterer. The recovered correlations carry comprehensive information about the spectral, spatial, and temporal coherence of the SPPs. We also introduce and exemplify for the first time, to the best of our knowledge, the twopoint Stokes parameters associated with partially coherent SPP fields. (C) 2017 Optical Society of America
Quantum communication with coherent states of light
Imran Khan, Dominique Elser, Thomas Dirmeier, Christoph Marquardt, Gerd Leuchs
PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY AMATHEMATICAL PHYSICAL
AND ENGINEERING SCIENCES
375(2099)
20160235
(2017)

Journal
Quantum communication offers longterm security especially, but not only, relevant to government and industrial users. It is worth noting that, for the first time in the history of cryptographic encoding, we are currently in the situation that secure communication can be based on the fundamental laws of physics ( information theoretical security) rather than on algorithmic security relying on the complexity of algorithms, which is periodically endangered as standard computer technology advances. On a fundamental level, the security of quantum key distribution (QKD) relies on the nonorthogonality of the quantum states used. So even coherent states are well suited for this task, the quantum states that largely describe the light generated by laser systems. Depending on whether one uses detectors resolving single or multiple photon states or detectors measuring the field quadratures, one speaks of, respectively, a discrete or a continuousvariable description. Continuousvariable QKD with coherent states uses a technology that is very similar to the one employed in classical coherent communication systems, the backbone of today's Internet connections. Here, we review recent developments in this field in two connected regimes: (i) improving QKD equipment by implementing frontend telecom devices and (ii) research into satellite QKD for bridging long distances by building upon existing optical satellite links.
This article is part of the themed issue 'Quantum technology for the 21st century'.
Effect of stray fields on Rydberg states in hollowcore PCF probed by
higherorder modes
G. Epple, N. Y. Joly, T. G. Euser, P. St. J. Russell, R. Loew
The spectroscopy of atomic gases confined in hollowcore photonic crystal fiber (HCPCF) provides optimal atomlight coupling beyond the diffraction limit, which is desirable for various applications such as sensing, referencing, and nonlinear optics. Recently, coherent spectroscopy was carried out on highly excited Rydberg states at room temperature in a gasfilled HCPCF. The large polarizability of the Rydberg states made it possible to detect weak electric fields inside the fiber. In this Letter, we show that by combining highly excited Rydberg states with higherorder optical modes, we can gain insight into the distribution and underlying effects of these electric fields. Comparisons between experimental findings and simulations indicate that the fields are caused by the dipole moments of atoms adsorbed on the hollowcore wall. Knowing the origin of the electric fields is an important step towards suppressing them in future HCPCF experiments. Furthermore, a better understanding of the influence of adatoms will be advantageous for optimizing electricfieldsensitive experiments carried out in the vicinity of nearby surfaces. (C) 2017 Optical Society of America
Detection Loss Tolerant Supersensitive Phase Measurement with an SU(1,1) Interferometer
Mathieu Manceau, Gerd Leuchs, Farid Khalili, Maria Chekhova
In an unseeded SU(1,1) interferometer composed of two cascaded degenerate parametric amplifiers, with direct detection at the output, we demonstrate a phase sensitivity overcoming the shot noise limit by 2.3 dB. The interferometer is strongly unbalanced, with the parametric gain of the second amplifier exceeding the gain of the first one by a factor of 2, which makes the scheme extremely tolerant to detection losses. We show that by increasing the gain of the second amplifier, the phase supersensitivity of the interferometer can be preserved even with detection losses as high as 80%. This finding can considerably improve the stateoftheart interferometry, enable subshotnoise phase sensitivity in spectral ranges with inefficient detection, and allow extension to quantum imaging.
Acceleration of subrelativistic electrons with an evanescent optical
wave at a planar interface
M. Kozak, P. Beck, H. Deng, J. McNeur, N. Schoenenberger, C. Gaida, F. Stutzki, M. Gebhardt, J. Limpert, et al.
We report on a theoretical and experimental study of the energy transfer between an optical evanescent wave, propagating in vacuum along the planar boundary of a dielectric material, and a beam of subrelativistic electrons. The evanescent wave is excited via total internal reflection in the dielectric by an infrared (lambda = 2 mu m) femtosecond laser pulse. By matching the electron propagation velocity to the phase velocity of the evanescent wave, energy modulation of the electron beam is achieved. A maximum energy gain of 800 eV is observed, corresponding to the absorption of more than 1000 photons by one electron. The maximum observed acceleration gradient is 19 +/ 2 MeV/m. The striking advantage of this scheme is that a structuring of the acceleration element's surface is not required, enabling the use of materials with high laser damage thresholds that are difficult to nanostructure, such as SiC, Al2O3 or CaF2. (C) 2017 Optical Society of America
Temporal shaping of single photons enabled by entanglement
Valentin Averchenko, Denis Sych, Gerhard Schunk, Ulrich Vogl, Christoph Marquardt, Gerd Leuchs
We present a method to produce pure single photons with an arbitrary designed temporal shape in a heralded way. As an indispensable resource, the method uses pairs of timeenergy entangled photons. One photon of a pair undergoes temporal amplitudephase modulation according to the desired shape. Subsequent frequencyresolved detection of the modulated photon heralds its entangled counterpart in a pure quantum state. The temporal shape of the heralded photon is indirectly affected by the modulation in the heralding arm. We derive conditions for which the shape of the heralded photon is given by the modulation function. The method can be implemented with various sources of timeenergy entangled photons. In particular, using entangled photons from parametric downconversion the method provides a simple means to generate pure shaped photons with an unprecedented broad range of temporal durations, from tenths of femtoseconds to microseconds. This shaping of single photons will push forward the implementation of scalable multidimensional quantum information protocols, efficient photonmatter coupling, and quantum control at the level of single quanta.
Levitated Plasmonic Nanoantennas in an Aqueous Environment
Yazgan Tuna, Ji Tae Kim, HsuanWei Liu, Vahid Sandoghdar
We report on the manipulation of a plasmonic nanoantenna in an aqueous solution using an electrostatic trap created between a glass nanopipette and a substrate. By scanning a trapped gold nanosphere in the near field of a single colloidal quantum dot embedded under the substrate surface, we demonstrate about 8fold fluorescence enhancement over a lateral full width at half maximum of about 45 nm. We analyze our results with the predictions of numerical electromagnetic simulations under consideration of the electrostatic free energy in the trap. Our approach could find applications in a number of experiments, where plasmonic effects are employed at liquid solid interfaces.
Experimental realization of an absolute singlephoton source based on a
single nitrogen vacancy center in a nanodiamond
Beatrice Rodiek, Marco Lopez, Helmuth Hofer, Geiland Porrovecchio, Marek Smid, XiaoLiu Chu, Stephan Gotzinger, Vahid Sandoghdar, Sarah Lindner, et al.
We report on the experimental realization of an absolute singlephoton source based on a single nitrogen vacancy (NV) center in a nanodiamond at room temperature and on the calculation of its absolute spectral photon flux from experimental data. The singlephoton source was calibrated with respect to its photon flux and its spectral photon rate density. The photon flux was measured with a lownoise silicon photodiode traceable to the primary standard for optical flux, taking into account the absolute spectral power distribution using a calibrated spectroradiometer. The optical radiant flux is adjustable from 55 fW, which is almost the lowest detection limit for the silicon photodiode, and 75 fW, which is the saturation power of the NV center. These fluxes correspond to total photon flux rates between 190,000 photons per second and 260,000 photons per second, respectively. The singlephoton emission purity is indicated by a g((2))(0) value, which is between 0.10 and 0.23, depending on the excitation power. To our knowledge, this is the first singlephoton source absolutely calibrated with respect to its absolute optical radiant flux and spectral power distribution, traceable to the corresponding national standards via an unbroken traceability chain. The prospects for its application, e.g., for the detection efficiency calibration of singlephoton detectors as well as for use as a standard photon source in the low photon flux regime, are promising. (C) 2017 Optical Society of America
Small slot waveguide rings for onchip quantum optical circuits
Nir Rotenberg, Pierre Tuerschmann, Harald R. Haakh, DiegoMartin Cano, Stephan Goetzinger, Vahid Sandoghdar
Nanophotonic interfaces between single emitters and light promise to enable new quantum optical technologies. Here, we use a combination of finite element simulations and analytic quantum theory to investigate the interaction of various quantum emitters with slotwaveguide rings. We predict that for rings with radii as small as 1.44 mu m, with a Qfactor of 27,900, nearunity emitterwaveguide coupling efficiencies and emission enhancements on the order of 1300 can be achieved. By tuning the ring geometry or introducing losses, we show that realistic emitterring systems can be made to be either weakly or strongly coupled, so that we can observe Rabi oscillations in the decay dynamics even for micronsized rings. Moreover, we demonstrate that slot waveguide rings can be used to directionally couple emission, again with nearunity efficiency. Our results pave the way for integrated solidstate quantum circuits involving various emitters. (C) 2017 Optical Society of America
A SingleEmitter Gain Medium for Bright Coherent Radiation from a Plasmonic Nanoresonator
Pu Zhang, Igor Protsenko, Vahid Sandoghdar, XueWen Chen
We propose and demonstrate theoretically bright coherent radiation from a plasmonic nanoresonator powered by a single threelevel quantum emitter. By introducing a dualpump scheme in a Raman configuration for the threelevel system, we overcome the fast decay of nanoplasmons and achieve macroscopic accumulation of nanoplasmons on the plasmonic nanoresonator for stimulated emission. We utilize the optical antenna effect for efficient radiation of the nanoplasmons and predict photon emission rates of 100 THz with up to 10 ps duration pulses and GHz repetition rates with the consideration of possible heating issue. We show that the ultrafast nature of the nanoscopic coherent source allows for operation with solidstate emitters at room temperature in the presence of fast dephasing. We provide physical interpretations of the results and discuss their realization and implications for ultracompact integration of optoelectronics.
Strong plasmonic enhancement of biexciton emission: controlled coupling of a single quantum dot to a gold nanocone antenna
Korenobu Matsuzaki, Simon Vassant, HsuanWei Liu, Anke Dutschke, Bjoern Hoffmann, Xuewen Chen, Silke Christiansen, Matthew R. Buck, Jennifer A. Hollingsworth, et al.
Multiexcitonic transitions and emission of several photons per excitation comprise a very attractive feature of semiconductor quantum dots for optoelectronics applications. However, these higherorder radiative processes are usually quenched in colloidal quantum dots by Auger and other nonradiative decay channels. To increase the multiexcitonic quantum efficiency, several groups have explored plasmonic enhancement, so far with moderate results. By controlled positioning of individual quantum dots in the near field of gold nanocone antennas, we enhance the radiative decay rates of monoexcitons and biexcitons by 109 and 100 folds at quantum efficiencies of 60 and 70%, respectively, in very good agreement with the outcome of numerical calculations. We discuss the implications of our work for future fundamental and applied research in nanooptics.
High average power and singlecycle pulses from a midIR optical parametric chirped pulse amplifier
Ugaitz Elu, Matthias Baudisch, Hugo Pires, Francesco Tani, Michael H. Frosz, Felix Koettig, Alexey Ermolov, Philip St J. Russell, Jens Biegert
In attosecond and strongfield physics, the acquisition of data in an acceptable time demands the combination of high peak power with high average power. We report a 21 W midIR optical parametric chirped pulse amplifier (OPCPA) that generates 131 mu J and 97 fs (sub9cycle) pulses at a 160 kHz repetition rate and at a center wavelength of 3.25 mu m. Pulsetopulse stability of the carrier envelope phase (CEP)stable output is excellent with a 0.33% rms over 288 million pulses (30 min) and compression close to a single optical cycle was achieved through soliton selfcompression inside a gasfilled midIR antiresonantguiding photonic crystal fiber. Without any additional compression device, stable generation of 14.5 fs (1.35opticalcycle) pulses was achieved at an average power of 9.6 W. The resulting peak power of 3.9 GW in combination with the nearsinglecycle duration and intrinsic CEP stability makes our OPCPA a keyenabling technology for the next generation of extreme photonics, strongfield attosecond research, and coherent xray science. (C) 2017 Optical Society of America
Sascha Preu, Christian MuellerLandau, Stefan Malzer, Gottfried H. Doehler, Hong Lu, Arthur C. Gossard, Daniel SegoviaVargas, Alejandro RiveraLavado, Enrique L. GarciaMunoz
IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION
65(7)
34743480
(2017)

Journal
We have fibercoupled an array of nipnip superlattice photomixers using a fiber array of same pitch of 145 mu m. We experimentally investigate the effect of the finite size of the implemented silicon lens on the interference between the array elements in the far field. We compare the results from a geometry optimized for a collimated terahertz (THz) beam to theory and simulations. Further, beam steering is demonstrated by controlling the optical phase of the individual photomixers. Due to broadband antennas attached to each array element, the array is frequency tunable. It is exemplarily characterized at 165 and 310 GHz. Such arrays can overcome power limitations of individual photomixers. In contrast to bulky individually packaged free space solutions, this array can be packaged to a compact terahertz source, limited in size only by the size of the silicon lens. The investigated 2 x 2 array features a spot diameter (fullwidth at halfmaximum) of 12.1 mm at a distance of 19 cm at 310 GHz with a silicon lens of only 20mm diameter.
Generation of broadband midIR and UV light in gasfilled singlering hollowcore PCF
Marco Cassataro, David Novoa, Mehmet C. Guenendi, Nitin N. Edavalath, Michael H. Frosz, John C. Travers, Philip St. J. Russell
We report generation of an ultrafast supercontinuum extending into the midinfrared in gasfilled singlering hollowcore photonic crystal fiber (SRPCF) pumped by 1.7 mu m light from an optical parametric amplifier. The simple fiber structure offers shallow dispersion and flat transmission in the near and midinfrared, enabling the generation of broadband spectra extending from 270 nm to 3.1 mu m, with a total energy of a few mu J. In addition, we demonstrate the emission of ultraviolet dispersive waves whose frequency can be tuned simply by adjusting the pump wavelength. SRPCF thus constitutes an effective means of compressing and delivering tunable ultrafast pulses in the near and midinfrared spectral regions. (C) 2017 Optical Society of America
The Formation of Calcified Nanospherites during Micropetrosis Represents a Unique Mineralization Mechanism in Aged Human Bone
Petar Milovanovic, Elizabeth A. Zimmermann, Annika vom Scheidt, Bjoern Hoffmann, George Sarau, Timur Yorgan, Michaela Schweizer, Michael Amling, Silke Christiansen, et al.
Osteocytesthe central regulators of bone remodelingare enclosed in a network of microcavities (lacunae) and nanocanals (canaliculi) pervading the mineralized bone. In a hitherto obscure process related to aging and disease, local plugs in the lacunocanalicular network disrupt cellular communication and impede bone homeostasis. By utilizing a suite of highresolution imaging and physicsbased techniques, it is shown here that the local plugs develop by accumulation and fusion of calcified nanospherites in lacunae and canaliculi (micropetrosis). Two distinctive nanospherites phenotypes are found to originate from different osteocytic elements. A substantial deviation in the spherites' composition in comparison to mineralized bone further suggests a mineralization process unlike regular bone mineralization. Clearly, mineralization of osteocyte lacunae qualifies as a strong marker for degrading bone material quality in skeletal aging. The understanding of micropetrosis may guide future therapeutics toward preserving osteocyte viability to maintain mechanical competence and fracture resistance of bone in elderly individuals.
Complementarity and Polarization Modulation in Photon Interference
Andreas Norrman, Kasimir Blomstedt, Tero Setala, Ari T. Friberg
We derive two general complementarity relations for the distinguishability and visibility of genuine vectorlight quantum fields in doublepinhole photon interference involving polarization modulation. The established framework reveals an intrinsic aspect of waveparticle duality of the photon, not previously reported, thus providing deeper insights into foundational quantum interference physics.
Extracting the physical sector of quantum states
D. Mogilevtsev, Y. S. Teo, J. Rehacek, Z. Hradil, J. Tiedau, R. Kruse, G. Harder, C. Silberhorn, L. L. SanchezSoto
The physical nature of any quantum source guarantees the existence of an effective Hilbert space of finite dimension, the physical sector, in which its state is completely characterized with arbitrarily high accuracy. The extraction of this sector is essential for state tomography. We show that the physical sector of a state, defined in some prechosen basis, can be systematically retrieved with a procedure using only data collected from a set of commuting quantum measurement outcomes, with no other assumptions about the source. We demonstrate the versatility and efficiency of the physicalsector extraction by applying it to simulated and experimental data for quantum light sources, as well as quantum systems of finite dimensions.
LempelZiv Complexity of Photonic Quasicrystals
Juan J. Monzon, Angel Felipe, Luis L. SanchezSoto
The properties of onedimensional photonic quasicrystals ultimately rely on their nontrivial longrange order, a hallmark that can be quantified in many ways depending on the specific aspects to be studied. Here, we assess the quasicrystal structural features in terms of the LempelZiv complexity. This is an easily calculable quantity that has proven to be useful for describing patterns in a variety of systems. One feature of great practical relevance is that it provides a reliable measure of how hard it is to create the structure. Using the generalized Fibonacci quasicrystals as our thread, we give analytical fitting formulas for the dependence of the optical response with the complexity.
Effect of ammonification temperature on the formation of coaxial GaN/Ga2O3 nanowires
Mukesh Kumar, George Sarau, Martin Heilmann, Silke Christiansen, Vikram Kumar, R. Singh
JOURNAL OF PHYSICS DAPPLIED PHYSICS
50(3)
035302
(2017)

Journal
The effect of ammonification temperature on the formation of coaxial GaN/Ga2O3 nanowires from betaGa2O3 nanowires is reported in this work. High quality wurtzite GaN material showing a single cplane phase is achieved from betaGa2O3 nanowires having monoclinic crystal structure at a high ammonification temperature of 1050 degrees C. Lower ammonification temperatures such as 900 degrees C are also adequate for achieving coaxial GaN/Ga2O3 nanowire heterostructures, and the degree of GaN phase can be adjusted by varying the ammonification temperature. The crystalline quality of GaN/Ga2O3 nanowires improves with increasing the ammonification temperature. Resonant Raman spectra of GaN/Ga2O3 nanowires show Raman progression through multiple longitudinalopticalphonon modes with overtones of up to second order. The development and improvement of the emission peak toward the near band edge of GaN at different ammonification temperatures were investigated using cathodoluminescence and photoluminescence characterization.
Understanding GaN/InGaN coreshell growth towards high quality factor
whispering gallery modes from nonpolar InGaN quantum wells on GaN rods
C. Tessarek, S. Rechberger, C. Dieker, M. Heilmann, E. Spiecker, S. Christiansen
GaN microrods are used as a basis for subsequent InGaN quantum well (QW) and quantum dot deposition by metalorganic vapor phase epitaxy. The coverage of the shell along the sidewall of rods is dependent on the rod growth time and a complete coverage is obtained for shorter rod growth times. Transmission electron microscopy measurements are performed to reveal the structural properties of the InGaN layer on the sidewall facet and on the top facet. The presence of layers in the microrod and on the microrod surface will be discussed with respect to GaN and InGaN growth. A detailed model will be presented explaining the formation of multiple SiN layers and the partial and full coverage of the shell around the core. Cathodoluminescence measurements are performed to analyze the InGaN emission properties along the microrod and to study the microresonator properties of such hexagonal coreshell structures. High quality factor whispering gallery modes with Q similar to 1200 are reported for the first time in a GaN microrod/InGaN nonpolar QW coreshell geometry. The GaN/InGaN coreshell microrods are expected to be promising building blocks for lowthreshold laser diodes and ultrasensitive optical sensors.
PHzWide Spectral Interference Through Coherent PlasmaInduced Fission of HigherOrder Solitons
F. Koettig, F. Tani, J. C. Travers, P. St. J. Russell
We identify a novel regime of solitonplasma interactions in which highintensity ultrashort pulses of intermediate soliton order undergo coherent plasmainduced fission. Experimental results obtained in gasfilled hollowcore photonic crystal fiber are supported by rigorous numerical simulations. In the anomalous dispersion regime, the cumulative blueshift of higherorder input solitons with ionizing intensities results in pulse splitting before the ultimate selfcompression point, leading to the generation of robust pulse pairs with PHz bandwidths. The novel dynamics closes the gap between plasmainduced adiabatic soliton compression and modulational instability.
Broadband, Lensless, and Optomechanically Stabilized Coupling into Microfluidic HollowCore Photonic Crystal Fiber Using Glass Nanospike
Richard Zeltner, Shangran Xie, Riccardo Pennetta, Philip St J. Russell
We report a novel technique for launching broadband laser light into liquidfilled hollowcore photonic crystal fiber (HCPCF). It uniquely offers self alignment and selfstabilization via optomechanical trapping of a,fused silica nanospike, fabricated by thermally tapering and chemically etching a single mode fiber into a tip diameter of 350 nm. We show that a trapping laser, deliirering similar to 300 mW at 1064 nm, can be used to optically align and stably maintain the iianospike at the core center. Once this is done, a weak broadband supercontinuum signal (similar to 5751064 nm) can be efficiently and close to achromatically launched in the HCPCF. The system is robust against liquidflow in either direction inside the HCPCF, and the Fresnel backreflections are reduced to negligible levels compared to freespace launching or buttcoupling. The results are of potential relevance for any application where the efficient delivery of broadband light into liquidcore waveguides is desired.
Photochemistry in a softglass singlering hollowcore photonic crystal fibre
Ana M. Cubillas, Xin Jiang, Tijmen G. Euser, Nicola Taccardi, Bastian J. M. Etzold, Peter Wasserscheid, Philip St. J. Russell
A hollowcore photonic crystal fibre (HCPCF), guided by photonic bandgap effects or antiresonant reflection, offers strong light confinement and long photochemical interaction lengths in a microscale channel filled with a solvent of refractive index lower than that of glass (usually fused silica). These unique advantages have motivated its recent use as a highly efficient and versatile microreactor for liquidphase photochemistry and catalysis. In this work, we use a singlering HCPCF made from a highindex soft glass, thus enabling photochemical experiments in higher index solvents. The optimized lightmatter interaction in the fibre is used to strongly enhance the reaction rate in a proofofprinciple photolysis reaction in toluene.
Refractometrybased air pressure sensing using glass microspheres as highQ whisperinggallery mode microresonators
Arturo Bianchetti, Alejandro Federico, Serge Vincent, Sivaraman Subramanian, Frank Vollmer
In this work a refractometric air pressure sensing platform timed on spherical whisperinggallery mode microresonators is presented and analyzed. The sensitivity of this sensing approach is characterized by measuring the whisperinggallery mode spectral shifts caused by a change of air refractive index produced by dynamic sinusoidal pressure variations that lie between extremes of +/ 1.81 kPa. A theoretical frame of work is developed to characterize the refractometric air pressure sensing platform by using the Ciddor equation for the refractive index of air, and a comparison is made against experimental results for the purpose of performance evaluation.
The emission rate of a point dipole can be strongly increased in the presence of a welldesigned optical antenna. Yet, optical antenna design is largely based on radiofrequency rules, ignoring, e.g., Ohmic losses and nonnegligible field penetration in metals at optical frequencies. Here, we combine reciprocity and Poynting's theorem to derive a set of opticalfrequency antenna design rules for benchmarking and optimizing the performance of optical antennas driven by single quantum emitters. Based on these findings a novel plasmonic cavity antenna design is presented exhibiting a considerably improved performance compared to a reference twowire antenna. Our work will be useful for the design of highperformance optical antennas and nanoresonators for diverse applications ranging from quantum optics to antennaenhanced singleemitter spectroscopy and sensing.
Midinfrared dispersive wave generation in gasfilled photonic crystal fibre by transient ionizationdriven changes in dispersion
F. Koettig, D. Novoa, F. Tani, M. C. Guenendi, M. Cassataro, J. C. Travers, P. St. J. Russell
Gasfilled hollowcore photonic crystal fibre is being used to generate ever wider supercontinuum spectra, in particular via dispersive wave emission in the deep and vacuum ultraviolet, with a multitude of applications. Dispersive waves are the result of nonlinear transfer of energy from a selfcompressed soliton, a process that relies crucially on phasematching. It was recently predicted that, in the strongfield regime, the additional transient anomalous dispersion introduced by gas ionization would allow phasematched dispersive wave generation in the midinfraredsomething that is forbidden in the absence of free electrons. Here we report the experimental observation of such midinfrared dispersive waves, embedded in a 4.7octavewide supercontinuum that uniquely reaches simultaneously to the vacuum ultraviolet, with up to 1.7W of total average power.
Free space excitation of coupled Andersonlocalized modes in photonic
crystal waveguides with polarization tailored beam
Ali Mahdavi, Paul Roth, Jolly Xavier, Taofiq K. Paraiso, Peter Banzer, Frank Vollmer
We experimentally demonstrate free space excitation of coupled Andersonlocalized modes in photonic crystal (PhC) linedefect waveguides (W1) with polarization tailored beams. The corresponding light beam is tightly focused on a pristine W1, and outofplane scattering is imaged. By integrating the scattering spectra along the guide, at the W1 modal cutoff, Andersonlocalized cavities are observed due to residual W1 fabricationdisorder. Their spectral lines exhibit high quality Q factors up to 2 x 10(5). The incident beam polarization and scattering intensities of the localized modes characterize the efficiency of freespace coupling. The coupling is studied for linearly and radially polarized input beams and for different input coupling locations along the W1 guide. The proposed coupling scheme is particularly attractive for excitation of PhC waveguide modes and Andersonlocalized cavities by beam steering and scanning microscopy for sensing applications. Published by AIP Publishing.
Using the focal phase to control attosecond processes
Dominik Hoff, Michael Krueger, Lothar Maisenbacher, Gerhard G. Paulus, Peter Hommelhoff, A. M. Sayler
The spatial evolution of the electric field of focused broadband light is crucial for many emerging attosecond technologies. Here the effects of the input beam parameters on the evolution of fewcycle laser pulses in the focus are discussed. Specifically, we detail how the frequencydependent input beam geometry, chirp and chromatic aberration can affect the spatial dependence of the carrierenvelope phase (CEP), central frequency and pulse duration in the focus. These effects are confirmed by a direct, threedimensional measurement of the CEPevolution in the focus of a typical fewcycle pulse laser using electron rescattering at metal nanotips in combination with a CEPmetre. Moreover, we demonstrate a simple measurement technique to estimate the focal CEP evolution by inputbeam parameters. These parameters can be used in novel ways in order to control attosecond dynamics and tailor highly nonlinear lightmatter interactions.
Orbital angular momentum modes of highgain parametric downconversion
Lina Beltran, Gaetano Frascella, Angela M. Perez, Robert Fickler, Polina R. Sharapova, Mathieu Manceau, Olga V. Tikhonova, Robert W. Boyd, Gerd Leuchs, et al.
Light beams with orbital angular momentum (OAM) are convenient carriers of quantum information. They can. also be. used for imparting rotational motion to particles and providing. high resolution in imaging. Due to the conservation of OAM in parametric downconversion (PDC), signal and idler photons generated at low gain have perfectly anticorrelated OAM values. It is interesting to study the OAM properties of highgain PDC, where the same OAM modes can be populated with large, but correlated, numbers of photons. Here we investigate the OAM spectrum of highgain PDC and show that the OAM mode content can be controlled by varying the pump power and the configuration of the source. In our experiment, we use a source consisting of two nonlinear crystals separated by an air gap. We discuss the OAM properties of PDC radiation emitted by this source and suggest possible modifications.
Noncritical generation of nonclassical frequency combs via spontaneous rotational symmetry breaking
Carlos NavarreteBenlloch, Giuseppe Patera, Germán J. de Valcarcel
Physical Review A
96(4)
043801
(2017)

Journal

PDF
Synchronously pumped optical parametric oscillators (SPOPOs) are optical cavities driven by modelocked lasers, and containing a nonlinear crystal capable of downconverting a frequency comb to lower frequencies. SPOPOs have received a lot of attention lately because their intrinsic multimode nature makes them compact sources of quantum correlated light with promising applications in modern quantum information technologies. In this work we show that SPOPOs are also capable of accessing the challenging and interesting regime where spontaneous symmetry breaking confers strong nonclassical properties to the emitted light, which has eluded experimental observation so far. Apart from opening the possibility of studying experimentally this elusive regime of dissipative phase transitions, our predictions will have a practical impact, since we show that spontaneous symmetry breaking provides a specific spatiotemporal mode with large quadrature squeezing for any value of the system parameters, turning SPOPOs into robust sources of highly nonclassical light above threshold.
Coherent Coupling of a Single Molecule to a Scanning FabryPerot
Microcavity
Daqing Wang, Hrishikesh Kelkar, DiegoMartin Cano, Tobias Utikal, Stephan Goetzinger, Vahid Sandoghdar
Organic dye molecules have been used in a great number of scientific and technological applications, but their wider use in quantum optics has been hampered by transitions to shortlived vibrational levels, which limit their coherence properties. To remedy this, one can take advantage of optical resonators. Here, we present the first results on coherent moleculeresonator coupling, where a single polycyclic aromatic hydrocarbon molecule extinguishes 38% of the light entering a microcavity at liquid helium temperature. We also demonstrate fourfold improvement of singlemolecule stimulated emission compared to freespace focusing and take first steps for coherent mechanical manipulation of the molecular transition. Our approach of coupling molecules to an open and tunable microcavity with a very low mode volume and moderately low quality factors of the order of 10(3) paves the way for the realization of nonlinear and collective quantum optical effects.
Continuously wavelengthtunable high harmonic generation via soliton dynamics
Francesco Tani, Michael H. Frosz, John C. Travers, Philip St. J. Russell
We report the generation of high harmonics in a gas jet pumped by pulses selfcompressed in a Hefilled hollowcore photonic crystal fiber through the soliton effect. The gas jet is placed directly at the fiber output. As the energy increases, the ionizationinduced soliton blueshift is transferred to the high harmonics, leading to emission bands that are continuously tunable from 17 to 45 eV. (C) 2017 Optical Society of America
Higherorder mode suppression in twisted singlering hollowcore photonic crystal fibers
N. N. Edavalath, M. C. Guenendi, R. Beravat, G. K. L. Wong, M. H. Frosz, J. M. Menard, P. St. J. Russell
A hollowcore singlering photonic crystal fiber (SRPCF) consists of a ring of capillaries arranged around a central hollow core. Spinning the preform during drawing introduces a continuous helical twist, offering a novel means of controlling the modal properties of hollowcore SRPCF. For example, twisting geometrically increases the effective axial propagation constant of the LP01like modes of the capillaries, providing a means of optimizing the suppression of HOMs, which occurs when the LP11like core mode phasematches to the LP01like modes of the surrounding capillaries. (In a straight fiber, optimum suppression occurs for a capillarytocore diameter ratio d/D = 0.682.) Twisting also introduces circular birefringence (to be studied in a future Letter) and has a remarkable effect on the transverse intensity profiles of the higherorder core modes, forcing the twolobed LP11like mode in the untwisted fiber to become threefold symmetric in the twisted case. These phenomena are explored by means of extensive numerical modeling, an analytical model, and a series of experiments. Prismassisted sidecoupling is used to measure the losses, refractive indices, and nearfield patterns of individual fiber modes in both the straight and twisted cases. (C) 2017 Optical Society of America
Generation of microjoule pulses in the deep ultraviolet at megahertz repetition rates
Felix Koettig, Francesco Tani, Christian MartensBiersach, John C. Travers, Philip St J. Russell
Although ultraviolet (UV) light is important in many areas of science and technology, there are very few if any lasers capable of delivering wavelengthtunable ultrashort UV pulses at high repetition rates. Here we report the generation of deep UV laser pulses at megahertz repetition rates and microjoule energies by means of dispersive wave (DW) emission from selfcompressed solitons in gasfilled singlering hollowcore photonic crystal fiber (SRPCF). Pulses from an ytterbium fiber laser (similar to 300 fs) are first compressed to <25 fs in a SRPCFbased nonlinear compression stage and subsequently used to pump a second SRPCF stage for broadband DW generation in the deep UV. The UV wavelength is tunable by selecting the gas species and the pressure. Through rigorous optimization of the system, in particular employing a largecore fiber filled with light noble gases, we achieve 1 mu J pulse energies in the deep UV, which is more than 10 times higher, at average powers more than four orders of magnitude greater (reaching 1 W) than previously demonstrated, with only 20 mu J pulses from the pump laser. (C) 2017 Optical Society of America
Flexible femtosecond inscription of fiber Bragg gratings by an optimized deformable mirror
Thorsten A. Goebel, Christian Voigtlaender, Ria G. Kraemer, Daniel Richter, Maximilian Heck, Malte P. Siems, Christian Matzdorf, Claudia Reinlein, Michael Appelfelder, et al.
The period of fiber Bragg gratings is adapted by shaping the wavefronts of ultrashort laser pulses applied in a phase mask inscription technique. A specially designed deformable mirror, based on a dielectric substrate to withstand high peak powers, is utilized to deform the wavefront. A shift of about 11 nm is demonstrated for a Bragg wavelength around 1550 nm. (c) 2017 Optical Society of America
Two observables are called complementary if preparing a physical object in an eigenstate of one of them yields a completely random result in a measurement of the other. We investigate small sets of complementary observables that cannot be extended by yet another complementary observable. We construct explicit examples of unextendible sets up to dimension 16 and conjecture certain small sets to be unextendible in higher dimensions. Our constructions provide three complementary measurements, only one observable away from the ultimate minimum of two. Almost all our examples in finite dimensions are useful for discriminating pure states from some mixed states, and they help to shed light on the complex topology of the Bloch space of higherdimensional quantum systems.
Dimensionality of random light fields
Andreas Norrman, Ari T. Friberg, Jose J. Gil, Tero Setala
JOURNAL OF THE EUROPEAN OPTICAL SOCIETYRAPID PUBLICATIONS
13
36
(2017)

Journal
Background: The spectral polarization state and dimensionality of random light are important concepts in modern optical physics and photonics.
Methods: By use of spacefrequency domain coherence theory, we establish a rigorous classification for the electricfield vector to oscillate in one, two, or three spatial dimensions.
Results: We also introduce a new measure, the polarimetric dimension, to quantify the dimensional character of light. The formalism is utilized to show that polarized threedimensional light does not exist, while an evanescent wave generated in total internal reflection generally is a genuine threedimensional light field.
Conclusions: The framework we construct advances the polarization theory of random light and it could be beneficial for nearfield optics and polarizationsensitive applications involving complexstructured light fields.
Highdimensional intracity quantum cryptography with structured photons
Alicia Sit, Frederic Bouchard, Robert Fickler, Jeremie GagnonBischoff, Hugo Larocque, Khabat Heshami, Dominique Elser, Christian Peuntinger, Kevin Guenthner, et al.
Quantum key distribution (QKD) promises informationtheoretically secure communication and is already on the verge of commercialization. The next step will be to implement highdimensional protocols in order to improve noise resistance and increase the data rate. Hitherto, no experimental verification of highdimensional QKD in the singlephoton regime has been conducted outside of the laboratory. Here, we report the realization of such a singlephoton QKD system in a turbulent freespace link of 0.3 km over the city of Ottawa, taking advantage of both the spin and orbital angular momentum photonic degrees of freedom. This combination of optical angular momenta allows us to create a 4dimensional quantum state; wherein, using a highdimensional BB84 protocol, a quantum bit error rate of 11% was attained with a corresponding secret key rate of 0.65 bits per sifted photon. In comparison, an error rate of 5% with a secret key rate of 0.43 bits per sifted photon is achieved for the case of 2dimensional structured photons. We thus demonstrate that, even through moderate turbulence without active wavefront correction, highdimensional photon states are advantageous for securely transmitting more information. This opens the way for intracity highdimensional quantum communications under realistic conditions. (C) 2017 Optical Society of America
Unconstrained Capacities of Quantum Key Distribution and Entanglement
Distillation for PureLoss Bosonic Broadcast Channels
Masahiro Takeoka, Kaushik P. Seshadreesan, Mark M. Wilde
We consider quantum key distribution (QKD) and entanglement distribution using a singlesender multiplereceiver pureloss bosonic broadcast channel. We determine the unconstrained capacity region for the distillation of bipartite entanglement and secret key between the sender and each receiver, whenever they are allowed arbitrary public classical communication. A practical implication of our result is that the capacity region demonstrated drastically improves upon rates achievable using a naive timesharing strategy, which has been employed in previously demonstrated network QKD systems. We show a simple example of a broadcast QKD protocol overcoming the limit of the pointtopoint strategy. Our result is thus an important step toward opening a new framework of network channelbased quantum communication technology.
Broadband highresolution multispecies CARS in gasfilled hollowcore photonic crystal fiber
Barbara M. Trabold, Robert J. R. Hupfer, Amir Abdolvand, Philip St. J. Russell
We report the use of coherent antiStokes Raman spectroscopy (CARS) in gasfilled hollowcore photonic crystal fiber (HCPCF) for trace gas detection. The long optical pathlengths yield a 60 dB increase in the signal level compared with freespace arrangements. This enables a relatively weak supercontinuum (SC) to be used as Stokes seed, along with a ns pump pulse, paving the way for broadband (> 4000 cm(1)) singleshot CARS with an unprecedented resolution of similar to 100 MHz. A kagomestyle HCPCF provides broadband guidance, and, by operating close to the pressuretunable zero dispersion wavelength, we can ensure simultaneous phasematching of all gas species. We demonstrate simultaneous measurement of the concentrations of multiple trace gases in a gas sample introduced into the core of the HCPCF. (C) 2017 Optical Society of America
Coherent control of flexural vibrations in dualnanoweb fibers using phasemodulated twofrequency light
J. R. Koehler, R. E. Noskov, A. A. Sukhorukov, D. Novoa, P. St. J. Russell
Coherent control of the resonant response in spatially extended optomechanical structures is complicated by the fact that the optical drive is affected by the backaction from the generated phonons. Here we report an approach to coherent control based on stimulated Ramanlike scattering, in which the optical pressure can remain unaffected by the induced vibrations even in the regime of strong optomechanical interactions. We demonstrate experimentally coherent control of flexural vibrations simultaneously along the whole length of a dualnanoweb fiber, by imprinting steps in the relative phase between the components of a twofrequency pump signal, the beat frequency being chosen to match a flexural resonance. Furthermore, sequential switching of the relative phase at time intervals shorter than the lifetime of the vibrations reduces their amplitude to a constant value that is fully adjustable by tuning the phase modulation depth and switching rate. The results may trigger new developments in silicon photonics, since such coherent control uniquely decouples the amplitude of optomechanical oscillations from powerdependent thermal effects and nonlinear optical loss.
Generic method for lossless generation of arbitrarily shaped photons
We put forward a generic method that enables lossless generation of pure single photons with arbitrary shape over any degree of freedom or several degrees of freedom simultaneously. The method exploits pairs of entangled photons. One of the photons is the subject for lossy shaping manipulations followed by a specially designed modeequalizing measurement. A successful measurement outcome heralds the losslessly shaped second photon. The method has three crucial ingredients that define the quantum state of the shaped photon: the initial bipartite state of the photons, modulation of the first photon, and its modeequalizing detection. We provide a specific recipe with a combination of these ingredients for achieving any desired pure state of the shaped photon.
Towards nextgeneration labelfree biosensors: recent advances in whispering gallery mode sensors
Whispering gallery mode biosensors have been widely exploited over the past decade to study molecular interactions by virtue of their high sensitivity and applicability in realtime kinetic analysis without the requirement to label. There have been immense research efforts made for advancing the instrumentation as well as the design of detection assays, with the common goal of progressing towards realworld sensing applications. We therefore review a set of recent developments made in this field and discuss the requirements that whispering gallery mode labelfree sensors need to fulfill for making a real world impact outside of the laboratory. These requirements are directly related to the challenges that these sensors face, and the methods proposed to overcome them are discussed. Moving forward, we provide the future prospects and the potential impact of this technology.
Extremely broadband singleshot crosscorrelation frequencyresolved optical gating using a transient grating as gate and dispersive element
H. ValtnaLukner, F. Belli, A. Ermolov, F. Koettig, K. F. Mak, F. Tani, J. C. Travers, P. St. J. Russell
REVIEW OF SCIENTIFIC INSTRUMENTS
88(7)
073106
(2017)

Journal
Acrosscorrelation frequencyresolved optical gating (FROG) concept, potentially suitable for characterizing few or subcycle pulses in a single shot, is described in which a counterpropagating transient grating is used as both the gate and the dispersive element in a FROG spectrometer. An allreflective setup, which can operate over the whole transmission range of the nonlinear medium, within the sensitivity range of the matrix sensor, is also proposed, and proofofprinciple experiments for the ultraviolet and visibletonearinfrared spectral ranges are reported. Published by AIP Publishing.
Phase sensitivity of gainunbalanced nonlinear interferometers
Enno Giese, Samuel Lemieux, Mathieu Manceau, Robert Fickler, Robert W. Boyd
The phase uncertainty of an unseeded nonlinear interferometer, where the output of one nonlinear crystal is transmitted to the input of a second crystal that analyzes it, is commonly said to be below the shotnoise level but highly dependent on detection and internal loss. Unbalancing the gains of the first (source) and second (analyzer) crystals leads to a configuration that is tolerant against detection loss. However, in terms of sensitivity, there is no advantage in choosing a stronger analyzer over a stronger source, and hence the comparison to a shotnoise level is not straightforward. Internal loss breaks this symmetry and shows that it is crucial whether the source or analyzer is dominating. Based on these results, claiming a Heisenberg scaling of the sensitivity is more subtle than in a balanced setup.
ChipBased AllOptical Control of Single Molecules Coherently Coupled to a Nanoguide
Pierre Tuerschmann, Nir Rotenberg, Jan Renger, Irina Harder, Olga Lohse, Tobias Utikal, Stephan Goetzinger, Vahid Sandoghdar
The feasibility of many proposals in nano quantumoptics depends on the efficient coupling of photons to individual quantum emitters, the possibility to control this interaction on demand, and the scalability of the experimental platform. To address these issues, we report on chipbased systems made of onedimensional subwavelength dielectric waveguides (nanoguides) and polycyclic aromatic hydrocarbon molecules. We discuss the design and fabrication requirements, present data on extinction spectroscopy of single molecules coupled to a nanoguide mode, and show how an external optical beam can switch the propagation of light via a nonlinear optical process. The presented architecture paves the way for the investigation of manybody phenomena and polaritonic states and can be readily extended to more complex geometries for the realization of quantum integrated photonic circuits.
Production of Isolated Giant Unilamellar Vesicles under High Salt
Concentrations
Hannah Stein, Susann Spindler, Navid Bonakdar, Chun Wang, Vahid Sandoghdar
The cell membrane forms a dynamic and complex barrier between the living cell and its environment. However, its in vivo studies are difficult because it consists of a high variety of lipids and proteins and is continuously reorganized by the cell. Therefore, membrane model systems with precisely controlled composition are used to investigate fundamental interactions of membrane components under welldefined conditions. Giant unilamellar vesicles (GUVs) offer a powerful model system for the cell membrane, but many previous studies have been performed in unphysiologically low ionic strength solutions which might lead to altered membrane properties, protein stability and lipidprotein interaction. In the present work, we give an overview of the existing methods for GUV production and present our efforts on forming single, free floating vesicles up to several tens of mu m in diameter and at high yield in various buffer solutions with physiological ionic strength and pH.
A single molecule as a highfidelity photon gun for producing
intensitysqueezed light
XiaoLiu Chu, Stephan Goetzinger, Vahid Sandoghdar
A twolevel atom cannot emit more than one photon at a time. As early as the 1980s, this quantum feature was identified as a gateway to 'singlephoton sources', where a regular excitation sequence would create a stream of light particles with photon number fluctuations below the shot noise(1). Such an intensitysqueezed beam of light would be desirable for a range of applications, such as quantum imaging, sensing, enhanced precision measurements and information processing(2,3). However, experimental realizations of these sources have been hindered by large losses caused by low photoncollection efficiencies and photophysical shortcomings. By using a planar metallodielectric antenna applied to an organic molecule, we demonstrate the most regular stream of single photons reported to date. The measured intensity fluctuations were limited by our detection efficiency and amounted to 2.2 dB squeezing.
Analytical formulation for the bend loss in singlering hollowcore photonic crystal fibers
Michael H. Frosz, Paul Roth, Mehmet C. Guenendi, Philip St. J. Russell
Understanding bend loss in singlering hollowcore photonic crystal fibers (PCFs) is becoming of increasing importance as the fibers enter practical applications. While purely numerical approaches are useful, there is a need for a simpler analytical formalism that provides physical insight and can be directly used in the design of PCFs with low bend loss. We show theoretically and experimentally that a wavelengthdependent critical bend radius exists below which the bend loss reaches a maximum, and that this can be calculated from the structural parameters of a fiber using a simple analytical formula. This allows straightforward design of singlering PCFs that are bendinsensitive for specified ranges of bend radius and wavelength. It also can be used to derive an expression for the bend radius that yields optimal higherorder mode suppression for a given fiber structure. (C) 2017 Chinese Laser Press
Multiphoton Effects Enhanced due to Ultrafast PhotonNumber Fluctuations
Kirill Yu. Spasibko, Denis A. Kopylov, Victor L. Krutyanskiy, Tatiana V. Murzina, Gerd Leuchs, Maria V. Chekhova
The rate of an nphoton effect generally scales as the nth order autocorrelation function of the incident light, which is high for light with strong photonnumber fluctuations. Therefore, "noisy" light sources are much more efficient for multiphoton effects than coherent sources with the same mean power, pulse duration, and repetition rate. Here we generate optical harmonics of the order of 24 from a bright squeezed vacuum, a state of light consisting of only quantum noise with no coherent component. We observe up to 2 orders of magnitude enhancement in the generation of optical harmonics due to ultrafast photonnumber fluctuations. This feature is especially important for the nonlinear optics of fragile structures, where the use of a noisy pump can considerably increase the effect without overcoming the damage threshold.
LaserPatterning Engineering for Perovskite Solar Modules With 95% Aperture Ratio
Alessandro Lorenzo Palma, Fabio Matteocci, Antonio Agresti, Sara Pescetelli, Emanuele Calabro, Luigi Vesce, Silke Christiansen, Michael Schmidt, Aldo Di Carlo
IEEE JOURNAL OF PHOTOVOLTAICS
7(6)
16741680
(2017)

Journal
Small area hybrid organometal halide perovskite based solar cells reached performances comparable to the multicrystalline silicon wafer cells. However, industrial applications require the scalingup of devices to modulesize. Here, we report the first fully laserprocessed large area (14.5 cm(2)) perovskite solar module with an aperture ratio of 95% and a power conversion efficiency of 9.3%. To obtain this result, we carried out thorough analyses and optimization of three laser processing steps required to realize the serial interconnection of various cells. By analyzing the statistics of the fabricated modules, we show that the error committed over the projected interconnection dimensions is sufficiently low to permit even higher aperture ratios without additional efforts.
Low temperature solidstate wetting and formation of nanowelds in silver nanowires
Vuk V. Radmilovic, Manuela Goebelt, Colin Ophus, Silke Christiansen, Erdmann Spiecker, Velimir R. Radmilovic
This article focuses on the microscopic mechanism of thermally induced nanoweld formation between silver nanowires (AgNWs) which is a key process for improving electrical conductivity in NW networks employed for transparent electrodes. Focused ion beam sectioning and transmission electron microscopy were applied in order to elucidate the atomic structure of a welded NW including measurement of the wetting contact angle and characterization of defect structure with atomic accuracy, which provides fundamental information on the welding mechanism. Crystal lattice strain, obtained by direct evaluation of atomic column displacements in high resolution scanning transmission electron microscopy images, was shown to be nonuniform among the five twin segments of the AgNW pentagonal structure. It was found that the pentagonal crosssectional morphology of AgNWs has a dominant effect on the formation of nanowelds by controlling initial wetting as well as diffusion of Ag atoms between the NWs. Due to complete solidstate wetting, at an angle of similar to 4.8 degrees, the welding process starts with homoepitaxial nucleation of an initial Ag layer on (100) surface facets, considered to have an infinitely large radius of curvature. However, the strong driving force for this process due to the GibbsThomson effect, requires the NW contact to occur through the corner of the pentagonal crosssection of the second NW providing a small radius of curvature. After the initial layer is formed, the welded zone continues to grow and extends out epitaxially to the neighboring twin segments.
Development of an optimal filter substrate for the identification of small microplastic particles in food by microRaman spectroscopy
Barbara E. Ossmann, George Sarau, Sebastian W. Schmitt, Heinrich Holtmannspoetter, Silke H. Christiansen, Wilhelm Dicke
ANALYTICAL AND BIOANALYTICAL CHEMISTRY
409(16)
40994109
(2017)

Journal
When analysing microplastics in food, due to toxicological reasons it is important to achieve clear identification of particles down to a size of at least 1 mu m. One reliable, optical analytical technique allowing this is microRaman spectroscopy. After isolation of particles via filtration, analysis is typically performed directly on the filter surface. In order to obtain high qualitative Raman spectra, the material of the membrane filters should not show any interference in terms of background and Raman signals during spectrum acquisition. To facilitate the usage of automatic particle detection, membrane filters should also show specific optical properties. In this work, beside eight different, commercially available membrane filters, three newly designed metalcoated polycarbonate membrane filters were tested to fulfil these requirements. We found that aluminiumcoated polycarbonate membrane filters had ideal characteristics as a substrate for microRaman spectroscopy. Its spectrum shows no or minimal interference with particle spectra, depending on the laser wavelength. Furthermore, automatic particle detection can be applied when analysing the filter surface under darkfield illumination. With this new membrane filter, analytics free of interference of microplastics down to a size of 1 mu m becomes possible. Thus, an important size class of these contaminants can now be visualized and spectrally identified.
FresnelReflectionFree SelfAligning Nanospike Interface between a StepIndex Fiber and a HollowCore PhotonicCrystalFiber Gas Cell
Riccardo Pennetta, Shangran Xie, Frances Lenahan, Manoj Mridha, David Novoa, Philip St. J. Russell
We report a fully integrated interface delivering efficient, reflectionfree, singlemode, and selfaligned coupling between a stepindex fiber and a gasfilled hollowcore photonic crystal fiber. The device offers a universal solution for interfacing solid and hollow cores and can be sealed to allow operation either evacuated or at high pressure. Stimulated Raman scattering and molecular modulation of light are demonstrated in a H2filled hollowcore photonic crystal fiber using the device.
Cathodoluminescence spectroscopy is a key analysis technique in nanophotonics research and technology, yet many aspects of its fundamental excitation mechanisms are not well understood on the singleelectron and singlephoton level. Here, we determine the cathodoluminescence emission statistics of InGaN quantum wells embedded in GaN under 630keV electron excitation and find that the light emission rate varies strongly from electron to electron. Strong photon bunching is observed for the InGaN quantum well emission at 2.77 eV due to the generation of multiple quantum well excitations by a single primary electron. The bunching effect, measured by the g((2))(t) autocorrelation function, decreases with increasing beam current in the range 3350 pA. Under pulsed excitation (p = 2100 ns; 0.136 electrons per pulse), the bunching effect strongly increases. A model based on Monte Carlo simulations is developed that assumes a fraction gamma of the primary electrons generates electronhole pairs that create multiple photons in the quantum wells. At a fixed primary electron energy (10 keV) the model explains all g(2) measurements for different beam currents and pulse durations using a single value for gamma= 0.5. At lower energies, when electrons cause mostly nearsurface excitations, gamma is reduced (gamma = 0.01 at 6 keV), which is explained by the presence of a AlGaN barrier layer that inhibits carrier diffusion to the buried quantum wells. The combination of g((2)) measurements in pulsed and continuous mode with spectral analysis provides a powerful tool to study optoelectronic properties and may find application in many other optically active systems and devices.
Potential of PEDOT: PSS as a hole selective front contact for silicon
heterojunction solar cells
Sara Jaeckle, Martin Liebhaber, Clemens Gersmann, Mathias Mews, Klaus Jaeger, Silke Christiansen, Klaus Lips
We show that the highly conductive polymer poly(3,4ethylenedioxythiophene)poly(styrenesulfonate) (PEDOT: PSS) can successfully be applied as a hole selective front contact in silicon heterojunction (SHJ) solar cells. In combination with a superior electron selective heterojunction back contact based on amorphous silicon (aSi), monocrystalline ntype silicon (cSi) solar cells reach power conversion efficiencies up to 14.8% and high opencircuit voltages exceeding 660 mV. Since in the PEDOT: PSS/cSi/ aSi solar cell the inferior hybrid junction is determining the electrical device performance we are capable of assessing the recombination velocity (v(I)) at the PEDOT: PSS/cSi interface. An estimated v(I) of similar to 400 cm/s demonstrates, that while PEDOT: PSS shows an excellent selectivity on ntype cSi, the passivation quality provided by the formation of a native oxide at the cSi surface restricts the performance of the hybrid junction. Furthermore, by comparing the measured external quantum efficiency with optical simulations, we quantify the losses due to parasitic absorption of PEDOT: PSS and reflection of the device layer stack. By pointing out ways to better passivate the hybrid interface and to increase the photocurrent we discuss the full potential of PEDOT: PSS as a front contact in SHJ solar cells.
CavityEnhanced Transport of Charge
David Hagenmueller, Johannes Schachenmayer, Stefan Schutz, Claudiu Genes, Guido Pupillo
We theoretically investigate charge transport through electronic bands of a mesoscopic onedimensional system, where interband transitions are coupled to a confined cavity mode, initially prepared close to its vacuum. This coupling leads to lightmatter hybridization where the dressed fermionic bands interact via absorption and emission of dressed cavity photons. Using a selfconsistent nonequilibrium Green's function method, we compute electronic transmissions and cavity photon spectra and demonstrate how lightmatter coupling can lead to an enhancement of charge conductivity in the steady state. We find that depending on cavity loss rate, electronic bandwidth, and coupling strength, the dynamics involves either an individual or a collective response of Bloch states, and we explain how this affects the current enhancement. We show that the charge conductivity enhancement can reach orders of magnitudes under experimentally relevant conditions.
Polarization and phaseshifting interferometry for arbitrary, locally
varying polarization states
Sergej Rothau, Christine Kellermann, Simon Mayer, Klaus Mantel, Norbert Lindlein
This publication presents what we believe is a novel interferometric method for the simultaneous measurement of the phase and state of polarization of a light wave with arbitrary polarization; in particular, it can be varying elliptical. The measurement strategy is based on variations of the reference wave, concerning phase and polarization and processing the interference patterns so obtained. With this method, which is very similar to classical phaseshifting interferometry, the general analysis of spatially variant states of polarization and their phase fronts can be done in one measurement cycle. Furthermore, the analysis of different optical elements regarding the impact on the polarization and phase of the incoming light can be realized. After the theoretical description of the method and the mathematical discussion of different algorithms, the realized measurement setup is presented. Afterward, the accuracy of the method is discussed.(C) 2017 Optical Society of America
Coarse graining the phase space of N qubits
Olivia Di Matteo, Luis L. SanchezSoto, Gerd Leuchs, Markus Grassl
We develop a systematic coarsegraining procedure for systems of N qubits. We exploit the underlying geometrical structures of the associated discrete phase space to produce a coarsegrained version with reduced effective size. Our coarsegrained spaces inherit key properties of the original ones. In particular, our procedure naturally yields a subset of the original measurement operators, which can be used to construct a coarse discrete Wigner function. These operators also constitute a systematic choice of incomplete measurements for the tomographer wishing to probe an intractably large system.
Quantum metrology at the limit with extremal Majorana constellations
F. Bouchard, P. de la Hoz, G. Bjork, R. W. Boyd, M. Grassl, Z. Hradil, E. Karimi, A. B. Klimov, G. Leuchs, et al.
Quantum metrology allows for a tremendous boost in the accuracy of measurement of diverse physical parameters. The estimation of a rotation constitutes a remarkable example of this quantumenhanced precision. The recently introduced Kings of Quantumness are especially germane for this task when the rotation axis is unknown, as they have a sensitivity independent of that axis and they achieve a Heisenberglimit scaling. Here, we report the experimental realization of these states by generating up to 21dimensional orbital angular momentum states of single photons, and confirm their high metrological abilities. (C) 2017 Optical Society of America.
Progress toward optimal quantum tomography with unbalanced homodyning
Balanced homodyning, heterodyning, and unbalanced homodyning are three wellknown sampling techniques used in quantum optics to characterize photonic sources in the continuousvariable regime. We show that for all quantum states and all observableparameter tomography schemes, which includes reconstructions of arbitrary operator moments and phasespace quasidistributions, localized sampling with unbalanced homodyning is always tomographically more powerful (gives more accurate estimators) than delocalized sampling with heterodyning. The latter is recently known to often give more accurate parameter reconstructions than conventional marginalized sampling with balanced homodyning. This result also holds for realistic photodetectors with subunit efficiency. With examples from firstthrough fourthmoment tomography, we demonstrate that unbalanced homodyning can outperform balanced homodyning when heterodyning fails to do so. This new benchmark takes us one step towards optimal continuousvariable tomography with conventional photodetectors and minimal experimental components.
Superiority of heterodyning over homodyning: An assessment with
quadrature moments
Y. S. Teo, C. R. Mueller, H. Jeong, Z. Hradil, J. Rehacek, L. L. SanchezSoto
We examine the momentreconstruction performance of both the homodyne and heterodyne (doublehomodyne) measurement schemes for arbitrary quantum states and introduce moment estimators that optimize the respective schemes for any given data. In the largedata limit, these estimators are as efficient as the maximumlikelihood estimators. We then illustrate the superiority of the heterodyne measurement for the reconstruction of the first and second moments by analyzing Gaussian states and many other significant nonclassical states. Finally, we present an extension of our theories to twomode sources, which can be straightforwardly generalized to all other multimode sources.
Multiparameter quantum metrology of incoherent point sources: Towards realistic superresolution
J. Rehacek, Z. Hradil, B. Stoklasa, M. Paur, J. Grover, A. Krzic, L. L. SanchezSoto
We establish the multiparameter quantum CramerRao bound for simultaneously estimating the centroid, the separation, and the relative intensities of two incoherent optical point sources using a linear imaging system. For equally bright sources, the CramerRao bound is independent of their separation, which confirms that the Rayleigh resolution limit is just an artifact of the conventional direct imaging and can be overcome with an adequate strategy. For the general case of unequally bright sources, the amount of information one can gain about the separation falls to zero, but we show that there is always a quadratic improvement in an optimal detection in comparison with the intensity measurements. This advantage can be of utmost importance in realistic scenarios, such as observational astronomy.
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