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 self-dual additive F4-codes of length n and minimum weight d from circulant graphs. The quantum codes with these parameters are constructed for the first time.
Intensity-intensity correlations determined by dimension of quantum state in phase space: P-distribution
Gerd Leuchs,
Roy J. Glauber,
Wolfgang P Schleich
Physica Scripta
90
(10)
108007
(2015)
| Journal
| PDF
Strong, spectrally-tunable chirality in diffractive metasurfaces
Israel De Leon,
Matthew J. Horton,
Sebastian A. Schulz,
Jeremy Upham,
Peter Banzer,
Robert W. Boyd
Metamaterials and metasurfaces provide a paradigm-changing approach for manipulating light. Their potential has been evinced by recent demonstrations of chiral responses much greater than those of natural materials. Here, we demonstrate theoretically and experimentally that the extrinsic chiral response of a metasurface can be dramatically enhanced by near-field diffraction effects. At the core of this phenomenon are lattice plasmon modes that respond selectively to the illumination’s polarization handedness. The metasurface exhibits sharp features in its circular dichroism spectra, which are tunable over a broad bandwidth by changing the illumination angle over a few degrees. Using this property, we demonstrate an ultra-thin circular-polarization sensitive spectral filter with a linewidth of ~10 nm, which can be dynamically tuned over a spectral range of 200 nm. Chiral diffractive metasurfaces, such as the one proposed here, open exciting possibilities for ultra-thin photonic devices with tunable, spin-controlled functionality.
Dimension of quantum phase space measured by photon correlations
Gerd Leuchs,
Roy J. Glauber,
Wolfgang P Schleich
Physica Scripta
90
(7)
074066
(2015)
| Journal
| PDF
Quantum-like nonseparable structures in optical beams
Andrea Aiello,
Falk Toeppel,
Christoph Marquardt,
Elisabeth Giacobino,
Gerd Leuchs
When two or more degrees of freedom become coupled in a physical system, a number of observables of the latter cannot be represented by mathematical expressions separable with respect to the different degrees of freedom. In recent years it appeared clear that these expressions may display the same mathematical structures exhibited by multiparty entangled states in quantum mechanics. In this work, we investigate the occurrence of such structures in optical beams, a phenomenon that is often referred to as 'classical entanglement'. We present a unified theory for different kinds of light beams exhibiting classical entanglement and we indicate several possible extensions of the concept. Our results clarify and shed new light upon the physics underlying this intriguing aspect of classical optics.
Risk Analysis of Trojan-Horse Attacks on Practical Quantum Key
Distribution Systems
Nitin Jain,
Birgit Stiller,
Imran Khan,
Vadim Makarov,
Christoph Marquardt,
Gerd Leuchs
IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS
21
(3)
6600710
(2015)
| Journal
An eavesdropper Eve may probe a quantum key distribution (QKD) system by sending a bright pulse from the quantum channel into the system and analyzing the back-reflected pulses. Such Trojan-horse attacks can breach the security of the QKD system, if appropriate safeguards are not installed or if they can be fooled by the Eve. We present a risk analysis of such attacks based on extensive spectral measurements, such as transmittance, reflectivity, and detection sensitivity of some critical components used in a typical QKD systems. Our results indicate the existence of wavelength regimes, where the attacker gains considerable advantage as compared to launching an attack at 1550 nm. We also propose countermeasures to reduce the risk of such attacks.
Measuring the Transverse Spin Density of Light
Martin Neugebauer,
Thomas Bauer,
Andrea Aiello,
Peter Banzer
We generate tightly focused optical vector beams whose electric fields spin around an axis transverse to the beams' propagation direction. We experimentally investigate these fields by exploiting the directional near-field interference of a dipolelike plasmonic field probe placed adjacent to a dielectric interface. This directionality depends on the transverse electric spin density of the excitation field. Near-to far-field conversion mediated by the dielectric interface enables us to detect the directionality of the emitted light in the far field and, therefore, to measure the transverse electric spin density with nanoscopic resolution. Finally, we determine the longitudinal electric component of Belinfante's elusive spin momentum density, a solenoidal field quantity often referred to as "virtual."
In this work, we theoretically and experimentally investigate the thermal response of whispering gallery mode microresonators operating in an aqueous glycerol medium. Thermal stabilisation of the resonance wavelength is realised by appropriate choice of the resonator radius and glycerol concentration, with a 60 fold reduction in thermal sensitivity demonstrated. Finally, we employ our stabilised system to determine the thermal dependence of the molecular polarisability of adsorbed bovine serum albumin molecules and the refractive index of dextran and poly(diallyldimethylammonium chloride) coatings. (C) 2015 AIP Publishing LLC.
Near-infrared single-photon spectroscopy of a whispering gallery mode
resonator using energy-resolving transition edge sensors
Michael Foertsch,
Thomas Gerrits,
Martin J. Stevens,
Dmitry Strekalov,
Gerhard Schunk,
Josef U. Fuerst,
Ulrich Vogl,
Florian Sedlmeir,
Harald G. L. Schwefel, et al.
We demonstrate a method to perform spectroscopy of near-infrared single photons without the need of dispersive elements. This method is based on a photon energy resolving transition edge sensor and is applied for the characterization of widely wavelength tunable narrow-band single photons emitted from a crystalline whispering gallery mode resonator. We measure the emission wavelength of the generated signal and idler photons with an uncertainty of up to 2 nm.
Selective switching of individual multipole resonances in single
dielectric nanoparticles
Following Mie theory, nanoparticles made of a high-refractive-index dielectric, such as silicon, exhibit a resonator-like behavior and very rich resonance spectra. Which electric or magnetic particle mode is excited depends on the wavelength, the refractive-index contrast relative to the environment, and the geometry of the nanoparticle itself. In addition, the spatial structure of the impinging light field plays a major role in the excitation of the nanoparticle resonances. Here, it is shown that, by tailoring the excitation field, individual multipole resonances can be selectively addressed while suppressing the excitation of other particle modes. This enables a detailed study of selected individual resonances without interference by the other modes.
Classically entangled optical beams for high-speed kinematic sensing
Stefan Berg-Johansen,
Falk Toeppel,
Birgit Stiller,
Peter Banzer,
Marco Ornigotti,
Elisabeth Giacobino,
Gerd Leuchs,
Andrea Aiello,
Christoph Marquardt
Tracking the kinematics of fast-moving objects is an important diagnostic tool for science and engineering. Here, we demonstrate an approach to positional and directional sensing based on the concept of classical entanglement in vector beams of light [Found. Phys. 28, 361 -374 (1998)]. The measurement principle relies on the intrinsic correlations existing in such beams between transverse spatial modes and polarization. The latter can be determined from intensity measurements with only a few fast photodiodes, greatly outperforming the bandwidth of current CCD/CMOS devices. In this way, our setup enables two-dimensional real-time sensing with temporal resolution in the GHz range. We expect the concept to open up new directions in metrology and sensing. (C) 2015 Optical Society of America
Practical implementation of mutually unbiased bases using quantum
circuits
The number of measurements necessary to perform the quantum state reconstruction of a system of qubits grows exponentially with the number of constituents, creating a major obstacle for the design of scalable tomographic schemes. We work out a simple and efficient method based on cyclic generation of mutually unbiased bases. The basic generator requires only Hadamard and controlled-phase gates, which are available in most practical realizations of these systems. We show how complete sets of mutually unbiased bases with different entanglement structures can be realized for three and four qubits. We also analyze the quantum circuits implementing the various entanglement classes.
Giant narrowband twin-beam generation along the pump-energy propagation
direction
Angela M. Perez,
Kirill Yu Spasibko,
Polina R. Sharapova,
Olga V. Tikhonova,
Gerd Leuchs,
Maria V. Chekhova
Walk-off effects, originating from the difference between the group and phase velocities, limit the efficiency of nonlinear optical interactions. While transverse walk-off can be eliminated by proper medium engineering, longitudinal walk-off is harder to avoid. In particular, ultrafast twin-beam generation via pulsed parametric down-conversion and four-wave mixing is only possible in short crystals or fibres. Here we show that in high-gain parametric down-conversion, one can overcome the destructive role of both effects and even turn them into useful tools for shaping the emission. In our experiment, one of the twin beams is emitted along the pump Poynting vector or its group velocity matches that of the pump. The result is markedly enhanced generation of both twin beams, with the simultaneous narrowing of angular and frequency spectrum. The effect will enable efficient generation of ultrafast twin photons and beams in cavities, waveguides and whispering-gallery mode resonators.
Projective filtering of the fundamental eigenmode from spatially
multimode radiation
A. M. Perez,
P. R. Sharapova,
S. S. Straupe,
F. M. Miatto,
O. V. Tikhonova,
G. Leuchs,
M. V. Chekhova
Lossless filtering of a single coherent (Schmidt) mode from spatially multimode radiation is a problem crucial for optics in general and for quantum optics in particular. It becomes especially important in the case of nonclassical light that is fragile to optical losses. An example is bright squeezed vacuum generated via high-gain parametric down conversion or four-wave mixing. Its highly multiphoton and multimode structure offers a huge increase in the information capacity provided that each mode can be addressed separately. However, the nonclassical signature of bright squeezed vacuum, photon-number correlations, are highly susceptible to losses. Here we demonstrate lossless filtering of a single spatial Schmidt mode by projecting the spatial spectrum of bright squeezed vacuum on the eigenmode of a single-mode fiber. Moreover, we show that the first Schmidt mode can be captured by simply maximizing the fiber-coupled intensity. Importantly, the projection operation does not affect the targeted mode and leaves it usable for further applications.
Goos-Hanchen and Imbert-Fedorov shifts for astigmatic Gaussian beams
In this work we investigate the role of the beam astigmatism in the Goos-Hanchen and Imbert-Fedorov shift. As a case study, we consider a Gaussian beam focused by an astigmatic lens and we calculate explicitly the corrections to the standard formulas for beam shifts due to the astigmatism induced by the lens. Our results show that the different focusing in the longitudinal and transverse direction introduced by an astigmatic lens may enhance the angular part of the shift.
Microconstriction Arrays for High-Throughput Quantitative Measurements of Cell Mechanical Properties
Janina R. Lange,
Julian Steinwachs,
Thorsten Kolb,
Lena A. Lautscham,
Irina Harder,
Graeme Whyte,
Ben Fabry
We describe a method for quantifying the mechanical properties of cells in suspension with a microfluidic device consisting of a parallel array of micron-sized constrictions. Using a high-speed charge-coupled device camera, we measure the flow speed, cell deformation, and entry time into the constrictions of several hundred cells per minute during their passage through the device. From the flow speed and the occupation state of the microconstriction array with cells, the driving pressure across each constriction is continuously computed. Cell entry times into microconstrictions decrease with increased driving pressure and decreased cell size according to a power law. From this power-law relationship, the cell elasticity and fluidity can be estimated. When cells are treated with drugs that depolymerize or stabilize the cytoskeleton or the nucleus, elasticity and fluidity data from all treatments collapse onto a master curve. Power-law rheology and collapse onto a master curve are predicted by the theory of soft glassy materials and have been previously shown to describe the mechanical behavior of cells adhering to a substrate. Our finding that this theory also applies to cells in suspension provides the foundation for a quantitative high-throughput measurement of cell mechanical properties with microfluidic devices.
Stars of the quantum Universe: extremal constellations on the Poincare
sphere
Gunnar Bjork,
Markus Grassl,
Pablo de la Hoz,
Gerd Leuchs,
Luis L. Sanchez-Soto
The characterization of the polarization properties of a quantum state requires the knowledge of the joint probability distribution of the Stokes variables. This amounts to assessing all the moments of these variables, which are aptly encoded in a multipole expansion of the density matrix. The cumulative distribution of these multipoles encapsulates in a handy manner the polarization content of the state. We work out the extremal states for that distribution, finding that SU(2) coherent states are maximal to any order, so they are the most polarized allowed by quantum theory. The converse case of pure states minimizing that distribution, which can be seen as the most quantum ones, is investigated for a diverse range of number of photons. Exploiting the Majorana representation, the problem appears to be closely related to distributing a number of points uniformly over the surface of the Poincare sphere.
Adjustable diffractive spiral phase plates
Walter Harm,
Stefan Bernet,
Monika Ritsch-Marte,
Irina Harder,
Norbert Lindlein
We report on the fabrication and the experimental demonstration of Moire diffractive spiral phase plates with adjustable helical charge. The proposed optical unit consists of two axially stacked diffractive elements of conjugate structure. The joint transmission function of the compound system corresponds to that of a spiral phase plate where the angle of mutual rotation about the central axis enables continuous adjustment of the helical charge. The diffractive elements are fabricated by gray-scale photolithography with a pixel size of 200 nm and 128 phase step levels in fused silica. We experimentally demonstrate the conversion of a TEM00 beam into approximated Laguerre-Gauss (LG) beams of variable helical charge, with a correspondingly variable radius of their ring-shaped intensity distribution. (C) 2015 Optical Society of America
A robust quantum receiver for phase shift keyed signals
The impossibility of perfectly discriminating non-orthogonal quantum states imposes far-reaching consequences both on quantum and classical communication schemes. We propose and numerically analyze an optimized quantum receiver for the discrimination of phase encoded signals. Our scheme outperforms the standard quantum limit and approaches the Helstrom bound for any signal power. The discrimination is performed via an optimized, feedback-mediated displacement prior to a photon counting detector. We provide a detailed analysis of the influence of excess noise and technical imperfections on the average error probability. The results demonstrate the receiver's robustness and show that it can outperform any classical receiver over a wide range of realistic parameters.
Entangling the Whole by Beam Splitting a Part
Callum Croal,
Christian Peuntinger,
Vanessa Chille,
Christoph Marquardt,
Gerd Leuchs,
Natalia Korolkova,
Ladislav Mista Jr.
A beam splitter is a basic linear optical element appearing in many optics experiments and is frequently used as a continuous-variable entangler transforming a pair of input modes from a separable Gaussian state into an entangled state. However, a beam splitter is a passive operation that can create entanglement from Gaussian states only under certain conditions. One such condition is that the input light is suitably squeezed. We demonstrate, experimentally, that a beam splitter can create entanglement even from modes which do not possess such a squeezing provided that they are correlated to, but not entangled with, a third mode. Specifically, we show that a beam splitter can create three-mode entanglement by acting on two modes of a three-mode fully separable Gaussian state without entangling the two modes themselves. This beam splitter property is a key mechanism behind the performance of the protocol for entanglement distribution by separable states. Moreover, the property also finds application in collaborative quantum dense coding in which decoding of transmitted information is assisted by interference with a mode of the collaborating party.
Optimal Frames for Polarization State Reconstruction
Complete determination of the polarization state of light requires at least four distinct projective measurements of the associated Stokes vector. Stability of state reconstruction, however, hinges on the condition number kappa of the corresponding instrument matrix. Optimization of redundant measurement frames with an arbitrary number of analysis states, m, is considered in this Letter in the sense of minimization of kappa. The minimum achievable kappa is analytically found and shown to be independent of m, except for m = 5 where this minimum is unachievable. Distribution of the optimal analysis states over the Poincare sphere is found to be described by spherical 2 designs, including the Platonic solids as special cases. Higher order polarization properties also play a key role in nonlinear, stochastic, and quantum processes. Optimal measurement schemes for nonlinear measurands of degree t are hence also considered and found to correspond to spherical 2t designs, thereby constituting a generalization of the concept of mutually unbiased bases.
Observation of optical polarization Mobius strips
Thomas Bauer,
Peter Banzer,
Ebrahim Karimi,
Sergej Orlov,
Andrea Rubano,
Lorenzo Marrucci,
Enrico Santamato,
Robert W. Boyd,
Gerd Leuchs
Mobius strips are three-dimensional geometrical structures, fascinating for their peculiar property of being surfaces with only one "side"-or, more technically, being "nonorientable" surfaces. Despite being easily realized artificially, the spontaneous emergence of these structures in nature is exceedingly rare. Here, we generate Mobius strips of optical polarization by tightly focusing the light beam emerging from a q-plate, a liquid crystal device that modifies the polarization of light in a space-variantmanner. Using a recently developed-method for the three-dimensional nanotomography of optical vector fields, we fully reconstruct the light polarization structure in the focal region, confirming the appearance of Mobius polarization structures. The preparation of such structured light modes may be important for complex light beam engineering and optical micro-and nanofabrication.
Intracavity Squeezing Can Enhance Quantum-Limited Optomechanical
Position Detection through Deamplification
V. Peano,
H. G. L. Schwefel,
Ch. Marquardt,
F. Marquardt
It has been predicted and experimentally demonstrated that by injecting squeezed light into an optomechanical device, it is possible to enhance the precision of a position measurement. Here, we present a fundamentally different approach where the squeezing is created directly inside the cavity by a nonlinear medium. Counterintuitively, the enhancement of the signal-to-noise ratio works by deamplifying precisely the quadrature that is sensitive to the mechanical motion without losing quantum information. This enhancement works for systems with a weak optomechanical coupling and/or strong mechanical damping. This can allow for larger mechanical bandwidth of quantum-limited detectors based on optomechanical devices. Our approach can be straightforwardly extended to quantum nondemolition qubit detection.
Quantum nature of Gaussian discord: Experimental evidence and role of
system-environment correlations
Vanessa Chille,
Niall Quinn,
Christian Peuntinger,
Callum Croal,
Ladislav Mista Jr.,
Christoph Marquardt,
Gerd Leuchs,
Natalia Korolkova
We provide experimental evidence of quantum features in bipartite states classified as entirely classical according to a conventional criterion based on the Glauber P function but possessing nonzero Gaussian quantum discord. Their quantum nature is experimentally revealed by acting locally on one part of the discordant state. We experimentally verify and investigate the effect of discord increase under the action of local loss and link it to the entanglement with the environment. Adding an environmental system purifying the state, we unveil the flow of quantum correlations within a global pure system using the Koashi-Winter inequality. For a discordant state generated by splitting a state in which the initial squeezing is destroyed by random displacements, we demonstrate the recovery of entanglement highlighting the role of system-environment correlations.
Classical polarization multipoles: paraxial versus nonparaxial
P. de la Hoz,
G. Bjork,
H. de Guise,
A. B. Klimov,
G. Leuchs,
L. L. Sanchez-Soto
We discuss the polarization of paraxial and nonparaxial classical light fields by resorting to a multipole expansion of the corresponding polarization matrix. It turns out that only a dipolar term contributes when one considers SU(2) (paraxial) or SU(3) (nonparaxial) as fundamental symmetries. In this latter case, one can alternatively expand in SU(2) multipoles, and then both a dipolar and a quadrupolar component contribute, which explains the richer structure of this nonparaxial instance. These multipoles uniquely determine Wigner functions, in terms of which we examine some intriguing hallmarks arising in this classical scenario.
Exploiting cellophane birefringence to generate radially and azimuthally
polarised vector beams
Johnston Kalwe,
Martin Neugebauer,
Calvine Ominde,
Gerd Leuchs,
Geoffrey Rurimo,
Peter Banzer
EUROPEAN JOURNAL OF PHYSICS
36
(2)
025011
(2015)
| Journal
We exploit the birefringence of cellophane to convert a linearly polarised Gaussian beam into either a radially or azimuthally polarised beam. For that, we fabricated a low-cost polarisation mask consisting of four segments of cellophane. The fast axis of each segment is oriented appropriately in order to rotate the polarisation of the incident linearly polarised beam as desired. To ensure the correct operation of the polarisation mask, we tested the polarisation state of the generated beam by measuring the spatial distribution of the Stokes parameters. Such a device is very cost efficient and allows for the generation of cylindrical vector beams of high quality.
We experimentally show an all-optical multipolar decomposition of the lowest-order eigenmodes of a single gold nanoprism using azimuthally and radially polarized cylindrical vector beams. By scanning the particle through these tailored field distributions, the multipolar character of the eigenmodes gets encoded into 2D-scanning intensity maps even for higher-order contributions to the eigenmode that are too weak to be discerned in the direct far-field scattering response. This method enables a detailed optical mode analysis of individual nanoparticles. (C) 2015 AIP Publishing LLC.
From transverse angular momentum to photonic wheels
Andrea Aiello,
Peter Banzer,
Martin Neugebauer,
Gerd Leuchs
NATURE PHOTONICS
9
(12)
789-795
(2015)
Scientists have known for more than a century that light possesses both linear and angular momenta along the direction of propagation. However, only recent advances in optics have led to the notion of spinning electromagnetic fields capable of carrying angular momenta transverse to the direction of motion. Such fields enable numerous applications in nano-optics, biosensing and near-field microscopy, including three-dimensional control over atoms, molecules and nanostructures, and allowing for the realization of chiral nanophotonic interfaces and plasmonic devices. Here, we report on recent developments of optics with light carrying transverse spin. We present both the underlying principles and the latest achievements, and also highlight new capabilities and future applications emerging from this young yet already advanced field of research.
Two-photon spectral amplitude of entangled states resolved in separable
Schmidt modes
A. Avella,
G. Brida,
M. Chekhova,
M. Gramegna,
A. Shurupov,
M. Genovese
The ability to access high dimensionality in Hilbert spaces represents a demanding key-stone for state-of-the-art quantum information. The manipulation of entangled states in continuous variables, wavevector as well frequency, represents a powerful resource in this sense. The number of dimensions of the Hilbert space that can be used in practical information protocols can be determined by the number of Schmidt modes that it is possible to address one by one. In the case of wavevector variables, the Schmidt modes can be losslessly selected using single-mode fibre and a spatial light modulator, but no similar procedure exists for the frequency space. The aim of this work is to present a technique to engineer the spectral properties of biphoton light, emitted via ultrafast spontaneous parametric down conversion, in such a way that the two-photon spectral amplitude (TPSA) contains several non-overlapping Schmidt modes, each of which can be filtered losslessly in frequency variables. Such TPSA manipulation is operated by a fine balancing of parameters like the pump frequency, the shaping of pump pulse spectrum, the dispersion dependence of spontaneous parametric down-conversion crystals as well as their length. Measurements have been performed exploiting the group velocity dispersion induced by the passage of optical fields through dispersive media, operating a frequency-to-time two-dimensional Fourier transform of the TPSA. Exploiting this kind of measurement we experimentally demonstrate the ability to control the Schmidt modes structure in TPSA through the pump spectrum manipulation.
Extremal states for photon number and quadratures as gauges for
nonclassicality
Z. Hradil,
J. Rehacek,
P. de la Hoz,
G. Leuchs,
L. L. Sanchez-Soto
Rotated quadratures carry the phase-dependent information of the electromagnetic field, so they are somehow conjugate to the photon number. We analyze this noncanonical pair, finding an exact uncertainty relation, as well as a couple of weaker inequalities obtained by relaxing some restrictions of the problem. We also find the intelligent states saturating that relation and complete their characterization by considering extra constraints on the second-order moments of the variables involved. Using these moments, we construct performance measures tailored to diagnose photon-added and Schrodinger-cat-like states, among others.
Loss-tolerant hybrid measurement test of CHSH inequality with weakly
amplified N00N states
Falk Toeppel,
Magdalena Stobinska
JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL
48
(7)
075306
(2015)
| Journal
Although our understanding of Bell's theorem and experimental techniques to test it have improved over the last 40 years, thus far all Bell tests have suffered at least from the detection or the locality loophole. Most photonic Bell tests rely on inefficient discrete-outcome measurements, often provided by photon counting detection. One possible way to close the detection loophole in photonic Bell tests is to involve efficient continuous-variable measurements instead, such as homodyne detection. Here, we propose a test of the Clauser-Horne-Shimony-Holt inequality that applies photon counting and homodyne detection on weakly amplified two-photon N00N states. The scheme suggested is remarkably robust against experimental imperfections and suits the limits of current technology. As amplified quantum states are considered, our work also contributes to the exploration of entangled macroscopic quantum systems. Further, it may constitute an alternative platform for a loophole-free Bell test, which is also important for quantum-technological applications.
We present a study of radially and azimuthally polarized Bessel-Gauss (BG) beams in both the paraxial and nonparaxial regime. We discuss the validity of the paraxial approximation and the form of the nonparaxial corrections for BG beams. We show that independently on the ratio between the Bessel aperture cone angle theta(0) and the Gaussian beam divergence theta(0), the nonparaxial corrections are alway very small and therefore negligible. The explicit expressions for the nonparaxial vector electric field components are also reported.
Quantum uncertainty in the beam width of spatial optical modes
Vanessa Chille,
Peter Banzer,
Andrea Aiello,
Gerd Leuchs,
Christoph Marquardt,
Nicolas Treps,
Claude Fabre
We theoretically investigate the quantum uncertainty in the beam width of transverse optical modes and, for this purpose, define a corresponding quantum operator. Single mode states are studied as well as multimode states with small quantum noise. General relations are derived, and specific examples of different modes and quantum states are examined. For the multimode case, we show that the quantum uncertainty in the beam width can be completely attributed to the amplitude quadrature uncertainty of one specific mode, which is uniquely determined by the field under investigation. This discovery provides us with a strategy for the reduction of the beam width noise by an appropriate choice of the quantum state. (C) 2015 Optical Society of America
Phase retrieval from carrier frequency interferograms: reduction of the
impact of space-variant disturbances
J. Schwider,
V. Nercissian,
K. Mantel
JOURNAL OF THE EUROPEAN OPTICAL SOCIETY-RAPID PUBLICATIONS
10
15003
(2015)
| Journal
Phase "extraction" by using temporal phase shifting is sensitive to vibrations and drifts, producing systematic phase errors periodic with twice the fringe frequency. This error source may be avoided by evaluating only single carrier frequency interferograms, which makes the procedure immune against vibrations and drifts provided that the integration time is short enough to freeze the fringe pattern. However, the phases extracted from single interferograms in this way often show local irregularities depending on the mean phase of the interference pattern. Such local phase irregularities are caused by local disturbances in the light path like specks and dust particles on the optical components of the interferometer. Moreover, since digitized data are gathered, there is a nonlinear processing step involved which is also responsible for the generation of such irregularities. Here, it is proposed to use a set of suitably combined phase-ramped interferograms to reduce phase dependent irregularities. The proposed averaging technique also reduces edge ringing effects known from Fourier evaluation procedures. Since the imaging optics also contributes to the phase to be measured when tilted wavefronts are used, calibration is mandatory. The calibrated state is only valid if strict rules considering fringe number per diameter as well as the position of the wedge in the interferometer are maintained in the measuring process.
Experimental Realization of Quantum Tomography of Photonic Qudits via
Symmetric Informationally Complete Positive Operator-Valued Measures
N. Bent,
H. Qassim,
A. A. Tahir,
D. Sych,
G. Leuchs,
L. L. Sanchez-Soto,
E. Karimi,
R. W. Boyd
Symmetric informationally complete positive operator-valued measures provide efficient quantum state tomography in any finite dimension. In this work, we implement state tomography using symmetric informationally complete positive operator-valued measures for both pure and mixed photonic qudit states in Hilbert spaces of orbital angular momentum, including spaces whose dimension is not power of a prime. Fidelities of reconstruction within the range of 0.81-0.96 are obtained for both pure and mixed states. These results are relevant to high-dimensional quantum information and computation experiments, especially to those where a complete set of mutually unbiased bases is unknown.
Quantum theory of an electromagnetic observer: Classically behaving
macroscopic systems and the emergence of the classical world in quantum
electrodynamics
L. I. Plimak,
Misha Ivanov,
A. Aiello,
S. Stenholm
Quantum electrodynamics under conditions of distinguishability of interactingmatter entities, and of controlled actions and back-actions between them, is considered. Such "mesoscopic quantum electrodynamics" is shown to share its dynamical structure with the classical stochastic electrodynamics. In formal terms, we demonstrate that all general relations of the mesoscopic quantum electrodynamics may be recast in a form lacking Planck's constant. Mesoscopic quantum electrodynamics is therefore subject to "doing quantum electrodynamics while thinking classically," allowing one to substitute essentially classical considerations for quantum ones without any loss in generality. Implications of these results for the quantum measurement theory are discussed.
Extremal quantum states and their Majorana constellations
G. Bjork,
A. B. Klimov,
P. de la Hoz,
M. Grassl,
G. Leuchs,
L. L. Sanchez-Soto
The characterization of quantum polarization of light requires knowledge of all the moments of the Stokes variables, which are appropriately encoded in the multipole expansion of the density matrix. We look into the cumulative distribution of those multipoles and work out the corresponding extremal pure states. We find that SU(2) coherent states are maximal to any order whereas the converse case of minimal states (which can be seen as the most quantum ones) is investigated for a diverse range of the number of photons. Taking advantage of the Majorana representation, we recast the problem as that of distributing a number of points uniformly over the surface of the Poincare sphere.
Optical Tracking of Anomalous Diffusion Kinetics in Polymer Microspheres
In this Letter we propose the use of whispering gallery mode resonance tracking as a label-free optical means to monitor diffusion kinetics in glassy polymer microspheres. Approximate solutions to the governing diffusion equations are derived for the case of slow relaxation and small Stefan number. Transduction of physical changes in the polymer, including formation of a rubbery layer, swelling, and dissolution, into detectable resonance shifts are described using a perturbative approach. Concrete examples of poly(methyl methacrylate) and polystyrene spheres in water are considered.
Schmidt modes in the angular spectrum of bright squeezed vacuum
P. Sharapova,
A. M. Perez,
O. V. Tikhonova,
M. V. Chekhova
We investigate both theoretically and experimentally strong correlations in macroscopic (bright) quantum states of light generated via unseeded parametric down-conversion and four-wave mixing. The states generated this way contain only quantum noise, without a classical component, and are referred to as bright squeezed vacuum (BSV). Their important advantage is the multimode structure, which offers a larger capacity for the encoding of quantum information. For the theoretical description of these states and their correlation features we introduce a generalized fully analytical approach, based on the concept of independent collective (Schmidt) modes and valid for the cases of both weak and strong nonlinear interaction. In experiment, we generate states of macroscopic BSV with up to 1010 photons per mode and examine large photon-number spatial correlations that are found to be very well described by our theoretical approach.
New Constructions of Codes for Asymmetric Channels via Concatenation
Markus Grassl,
Peter W. Shor,
Graeme Smith,
John Smolin,
Bei Zeng
IEEE TRANSACTIONS ON INFORMATION THEORY
61
(4)
1879-1886
(2015)
| Journal
We present new constructions of codes for asymmetric channels for both binary and nonbinary alphabets, based on methods of generalized code concatenation. For the binary asymmetric channel, our methods construct nonlinear single-error-correcting codes from ternary outer codes. We show that some of the Varshamov-Tenengol'ts-Constantin-Rao codes, a class of binary nonlinear codes for this channel, have a nice structure when viewed as ternary codes. In many cases, our ternary construction yields even better codes. For the nonbinary asymmetric channel, our methods construct linear codes for many lengths and distances which are superior to the linear codes of the same length capable of correcting the same number of symmetric errors.
Time-Reversal-Symmetric Single-Photon Wave Packets for Free-Space
Quantum Communication
Readout and retrieval processes are proposed for efficient, high-fidelity quantum state transfer between a matter qubit, encoded in the level structure of a single atom or ion, and a photonic qubit, encoded in a time-reversal-symmetric single-photon wave packet. They are based on controlling spontaneous photon emission and absorption of a matter qubit on demand in free space by stimulated Raman adiabatic passage. As these processes do not involve mode selection by high-finesse cavities or photon transport through optical fibers, they offer interesting perspectives as basic building blocks for free-space quantum-communication protocols.
Interfacing transitions of different alkali atoms and telecom bands
using one narrowband photon pair source
Gerhard Schunk,
Ulrich Vogl,
Dmitry V. Strekalov,
Michael Foertsch,
Florian Sedlmeir,
Harald G. L. Schwefel,
Manuela Goebelt,
Silke Christiansen,
Gerd Leuchs, et al.
Quantum information technology strongly relies on the coupling of optical photons with narrowband quantum systems, such as quantum dots, color centers, and atomic systems. This coupling requires matching the optical wavelength and bandwidth to the desired system, which presents a considerable problem for most available sources of quantum light. Here we demonstrate the coupling of alkali dipole transitions with a tunable source of photon pairs. Our source is based on spontaneous parametric downconversion in a triply resonant whispering gallery mode resonator. For this, we have developed novel wavelength-tuning mechanisms that allow a coarse tuning to either the cesium or rubidium wavelength, with subsequent continuous fine-tuning to the desired transition. As a demonstration of the functionality of the source, we performed a heralded single-photon measurement of the atomic decay. We present a major advance in controlling the spontaneous downconversion process, which makes our bright source of heralded single photons now compatible with a plethora of narrowband resonant systems. (C) 2015 Optical Society of America
Bright squeezed vacuum: Entanglement of macroscopic light beams
We discuss various methods to create macroscopic (bright) entangled light beams. As an example, bright squeezed vacuum is considered in detail. This state of light, obtained via high-gain parametric downconversion, manifests entanglement in both photon numbers and polarization. (C) 2014 Elsevier B.V. All rights reserved.
Raman-Free, Noble-Gas-Filled Photonic-Crystal Fiber Source for
Ultrafast, Very Bright Twin-Beam Squeezed Vacuum
Martin A. Finger,
Timur Sh. Iskhakov,
Nicolas Y. Joly,
Maria V. Chekhova,
Philip St. J. Russell
We report a novel source of twin beams based on modulational instability in high-pressure argon-filled hollow-core kagome-style photonic-crystal fiber. The source is Raman-free and manifests strong photonnumber correlations for femtosecond pulses of squeezed vacuum with a record brightness of similar to 2500 photons per mode. The ultra-broadband (similar to 50 THz) twin beams are frequency tunable and contain one spatial and less than 5 frequency modes. The presented source outperforms all previously reported squeezed-vacuum twin-beam sources in terms of brightness and low mode content.
Goos-Hanchen and Imbert-Fedorov shifts for paraxial X-waves
We present a theoretical analysis for the Goos-Hanchen and Imbert-Fedorov shifts experienced by an X-wave upon reflection from a dielectric interface. We show that the temporal chirp, as well as the bandwidth of the X-wave, directly affect the spatial shifts in a way that can be experimentally observed, while the angular shifts do not depend on the spectral features of the X-wave. A dependence of the spatial shifts on the spatial structure of the X-wave is also discussed. (C) 2015 Optical Society of America
Highly efficient generation of single-mode photon pairs from a
crystalline whispering-gallery-mode resonator source
Michael Foertsch,
Gerhard Schunk,
Josef U. Fuerst,
Dmitry Strekalov,
Thomas Gerrits,
Martin J. Stevens,
Florian Sedlmeir,
Harald G. L. Schwefel,
Sae Woo Nam, et al.
We report a highly efficient source of narrow-band photon pairs based on parametric down-conversion in a crystalline-whispering-gallery-mode resonator. Remarkably, each photon of a pair is detected in a single spatial and temporal mode, as witnessed by Glauber's autocorrelation function. We explore the phase-matching conditions in spherical geometries, and determine the requirements for single-mode operation. Understanding these conditions has allowed us to experimentally demonstrate a single-mode pair-detection efficiency of 1.13 x 10(6) pairs/s per mW pump power per 26.8 MHz bandwidth.
Whispering gallery mode sensors
Matthew R. Foreman,
Jon D. Swaim,
Frank Vollmer
ADVANCES IN OPTICS AND PHOTONICS
7
(2)
168-240
(2015)
| Journal
We present a comprehensive overview of sensor technology exploiting optical whispering gallery mode (WGM) resonances. After a short introduction we begin by detailing the fundamental principles and theory of WGMs in optical microcavities and the transduction mechanisms frequently employed for sensing purposes. Key recent theoretical contributions to the modeling and analysis of WGM systems are highlighted. Subsequently we review the state of the art of WGM sensors by outlining efforts made to date to improve current detection limits. Proposals in this vein are numerous and range, for example, from plasmonic enhancements and active cavities to hybrid optomechanical sensors, which are already working in the shot noise limited regime. In parallel to furthering WGM sensitivity, efforts to improve the time resolution are beginning to emerge. We therefore summarize the techniques being pursued in this vein. Ultimately WGM sensors aim for real-world applications, such as measurements of force and temperature, or alternatively gas and biosensing. Each such application is thus reviewed in turn, and important achievements are discussed. Finally, we adopt a more forward-looking perspective and discuss the outlook of WGM sensors within both a physical and biological context and consider how they may yet push the detection envelope further. (C) 2015 Optical Society of America
Note on the helicity decomposition of spin and orbital optical currents
In the helicity representation, the Poynting vector (current) for a monochromatic optical field, when calculated using either the electric or the magnetic field, separates into right-handed and left-handed contributions, with no cross-helicity contributions. Cross-helicity terms do appear in the orbital and spin contributions to the current. But when the electric and magnetic formulas are averaged ('electric-magnetic democracy'), these terms cancel, restoring the separation into right-handed and left-handed currents for orbital and spin separately.
Dielectric Rod Waveguide Antenna as THz Emitter for Photomixing Devices
Alejandro Rivera-Lavado,
Sascha Preu,
Luis Enrique Garcia-Munoz,
Andrey Generalov,
Javier Montero-de-Paz,
Gottfried Doehler,
Dmitri Lioubtchenko,
Mario Mendez-Aller,
Florian Sedlmeir, et al.
IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION
63
(3)
882-890
(2015)
| Journal
We propose a dielectric rod waveguide antenna (DRW) integrated with a photomixer as a THz emitter. This represents a different approach as opposed to the classical solution of a substrate lens. Main goals are an inexpensive alternative to substrate lenses, reduction of both reflections on the semiconductor-air interface and scattering of terahertz-generated power into the substrate. A radiation pattern measured at 137 GHz is shown as a proof-of-concept. In order to increase radiated power, the improvement of the rod antenna is discussed. Finally, as an application example, evanescent coupling of the DRW into a high index whispering gallery mode resonator is shown.
By performing quantum-noise-limited optical heterodyne detection, we observe polarization noise in light after propagation through a hollow-core photonic crystal fiber (PCF). We compare the noise spectrum to the one of a standard fiber and find an increase of noise even though the light is mainly transmitted in air in a hollow-core PCF. Combined with our simulation of the acoustic vibrational modes in the hollow-core PCF, we are offering an explanation for the polarization noise with a variation of guided acoustic wave Brillouin scattering (GAWBS). Here, instead of modulating the strain in the fiber core as in a solid core fiber, the acoustic vibrations in hollow-core PCF influence the effective refractive index by modulating the geometry of the photonic crystal structure. This induces polarization noise in the light guided by the photonic crystal structure. (C) 2015 Optical Society of America
Direct Schmidt number measurement of high-gain parametric down
conversion
I. V. Dyakonov,
P. R. Sharapova,
T. Sh Iskhakov,
G. Leuchs
In this work we estimate the transverse Schmidt number for the bipartite high-gain parametric down conversion state by means of second-order intensity correlation function measurement. Assuming that the number of modes is equal in both beams we determine the Schmidt number considering only one of the subsystems. The obtained results demonstrate that this approach is equally efficient over the whole propagation of the state from the near field to the far field regions of its emitter.
Quantum Uniqueness
Denis Sych,
Gerd Leuchs
FOUNDATIONS OF PHYSICS
45
(12)
1613-1619
(2015)
| Journal
Classical physics allows for the existence of pairs of absolutely identical systems. Pairwise application of identical measurements to each of those systems always leads to exactly alike results irrespectively of the choice of measurements. Here we ask a question how the picture looks like in the quantum domain. Surprisingly, we get a counterintuitive outcome. Pairwise application of identical (but a priori unknown) measurements cannot always lead to exactly alike results. We interpret this as quantum uniqueness-a feature that has no classical analog.
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