Quantum Optics

We present an experiment that probes polariton quantum correlations by exploiting quantum complementarity. Specifically, we find that polaritons in two distinct idler modes interfere if and only if they share the same signal mode so that ''which-way'' information cannot be gathered. The experimental results prove the existence of polariton pair correlations that store the which-way information. This interpretation is confirmed by a theoretical analysis of the measured interference visibility in terms of quantum Langevin equations.

We theoretically study classical step-modulated pulse propagation in an optically thick medium with electromagnetically induced transparency ͑EIT͒ using a fast Fourier transform and a proposed hybrid-asymptotic analysis. The 100% transmitted leading edge traveling at c consists of Sommerfeld-Brillouin precursors. The main signal, falling inside of the narrow EIT window, experiences a steep dispersion and slow group velocity. We suggest active control of the precursors and main signal separately by adjusting the parameters of the medium and incident pulse.

We describe a theoretical method to distinguish between the precursors ͑transient part͒ and main signal ͑steady state͒ for a Gaussian pulse propagating through an anomalously dispersive linear dielectric. According to conventional theory of optical precursors, there is no main signal for Gaussian pulse propagation regardless of the system parameters. In this paper, we show the existence of the main pulse by comparing the conventional asymptotic theory with recently published analytical expressions. Additionally, we show that experimentally observed, asymmetrically extended tails in Gaussian pulse propagation are due to a resonant precursor.

We theoretically study classical step-modulated pulse propagation in an optically thick medium with electromagnetically induced transparency ͑EIT͒ using a fast Fourier transform and a proposed hybrid-asymptotic analysis. The 100% transmitted leading edge traveling at c consists of Sommerfeld-Brillouin precursors. The main signal, falling inside of the narrow EIT window, experiences a steep dispersion and slow group velocity. We suggest active control of the precursors and main signal separately by adjusting the parameters of the medium and incident pulse.

We present an experimental validation of the Quantum Harmonic Resonance Framework (QHRF) using real superconducting quantum hardware provided by IBM Quantum. A 5-qubit resonator lattice was constructed, combining superposition initialization, progressive parametric resonance injection, and dynamic entanglement coupling. The results demonstrate highly selective stabilization of specific resonant quantum states, suppressing chaotic behavior, and preserving multi-mode entanglement across the network, confirming key QHRF predictions.

l h i r i r a prep~afapaperintendedforpub~~tionina j o d orproceedings Since changes may be made before publication, this preprint i s made available with the ~d e ~b n d i n g that it will not be Cited or reproduced without the permission of the .&r. This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or amme9 any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising o r product endorsement purposes.

The Barut-Girardello coherent states (BG CS) representation is extended to the noncompact algebras u(p, q) and sp(N, R) in (reducible) quadratic boson realizations. The sp(N, R) BG CS take the form of multimode ordinary Schrödinger cat states. Macroscopic superpositions of 2 n-1 sp(N, R) CS (2 n canonical CS, n = 1, 2, . . .) are pointed out which are overcomplete in the N -mode Hilbert space and the relation between the canonical CS and the u(p, q) BG-type CS representations is established. The sets of u(p, q) and sp(N, R) BG CS and their discrete superpositions contain many states studied in quantum optics (even and odd N -mode CS, pair CS) and provide an approach to quadrature squeezing, alternative to that of intelligent states. New subsets of weakly and strongly nonclassical states are pointed out and their statistical properties (first-and second-order squeezing, photon number distributions) are discussed. For specific values of the angle parameters and small amplitude of the canonical CS components these states approaches multimode Fock states with one, two or three bosons/photons. It is shown that eigenstates of a squared non-Hermitian operator A 2 (generalized cat states) can exhibit squeezing of the quadratures of A.

A vertical cavity surface emitting laser with saturable absorber can work as a cavity soliton laser. We show that the properties of the system are deeply influenced by the radiative recombination of carriers. The existence of solitons is shown numerically for a choice of parameters suitable to describe devices where the same material is used for the active and the passive parts.

The optical clock-transitions in Yb and Sr are prime candidates for encoding qubits for quantum information processing applications. Electric dipole oneand two-photon transitions between the extremely long-lived 1 S 0 and 3 P 0 states are dipole and parity forbidden, respectively. Whereas this results in highly desirable low-decoherence rates, it also represents the main problem for fast coherent manipulation and measurement of qubits for quantum information processing. In this work, we determine the feasibility of using a coherent, recoil-free, three-photon transition [1] for fast coherent rotation of qubits followed by ultrafast readout of the 3 P 0 state via photo ionization. Rapid control and measurement of atomic qubits are crucial for high-speed synchronization of quantum information processors. Furthermore, we explore the possibility of loophole free tests of Bell inequalities using spatially separated entangled qubits via fast measurements.

In this contribution we present a proof of concept for a femtosecond all-optical demultiplexer based on the diffraction of a pulsed laser beam by an ultrafast transient refractive index grating formed in barium fluoride. The instantaneous character of the grating is demonstrated by measuring the temporal response of the first diffracted order of an independent laser beam. We achieve an overall switching efficiency of > 23% (> 18% for m = 1), with an extremely high on-off contrast ratio. Our arrangement provides wavelength-dependent diffraction and shows its potential as a demultiplexer for wavelength division multiplexing.

The bilateral boundary conditions (15) and ( ) which we obtained are the solution of the stated problem. Since they were obtained in the Bourret approximation of the theory of multiple scattering, their region of applicability is thereby limited to the allowance for an infinite subsequence of multiple scatterings at random disturbed boundaries 5]. In a number of cases this proves sufficient, which makes them particularly convenient when studying fields formed as a result of multiple scattering on random disturbances, such as for wave propagation in open waveguides with statistically irregular boundaries. In particular, they can prove useful for the investigation of waves and signals in optical fibers having a stepwise variation of the index of refraction over the cross section, in which, as is known, the ohmic losses are now close to the theoretical lower limit, while unavoidable roughness of the boundaries can prove to be an important factor in losses and variation of the dispersion owing to accumulating effects resulting from scattering on roughness over long transmission lines.

The multiphoton states generated by high-gain spontaneous parametric down-conversion (SPDC) in presence of large losses are investigated theoretically and experimentally. The explicit form for the two-photon output state has been found to exhibit a Werner structure very resilient to losses for any value of the gain parameter, g. The theoretical results are found in agreement with the experimental data. The last ones are obtained by quantum tomography of the state generated by a high-gain SPDC.

Terahertz phase retrieval from a set of axially separated diffractive intensity distributions is a promising single-beam computational imaging technique that ensures the obtention of high spatial resolutions and phase wavefronts, but remains restricted by time-consuming data acquisition processes. In this work, we have adopted an approach, relying on the radiation of a quantum cascade laser and the implementation of an express single-scan measurement of intensity distributions through the continuous on-the-go displacement of a high-sensitivity antenna-coupled microbolometer sensor array. In addition to the simplicity of this practical implementation and the minimization of measurement times, such an approach overcomes the problem of preliminary optimal selections of transverse intensity distributions used in the iterative phase retrieval algorithm and guarantees the required data diversity for high-quality wavefront reconstruction.

We discuss the differences between two well-studied and related phenomena-coherent population trapping (CPT) and electromagnetically induced transparency (EIT). Many differences between the two-such as the effect of power in the beams, detuning of the beams from resonance, and the use of vapor cells filled with buffer gas-are demonstrated experimentally. The experiments are done using magnetic sublevels of the 1 → 1 transition in the D2 line of 87 Rb.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

A major challenge towards integrated quantum optics is the deterministic integration of quantum emitters on optical chips. Combining the quantum optical properties of some emitters with the benefits of integration and scalability of integrated optics is still a major issue to overcome. In this work, we demonstrate a novel approach in which quantum emitters are positioned in a controlled manner onto a substrate and onto an optical waveguide with nanoscale precision via direct laser writing based on two-photon polymerization (DLW-TPP). Our quantum emitters are colloidal CdSe/ZnS quantum dots (QDs) embedded in polymeric nanostructures. Varying the laser parameters during the patterning process, size-controlled QD-polymer nanostructures have been characterized systematically. Structures as small as 20 nm in height were fabricated. The well-controlled QD-polymer nanostructure systems were then successfully integrated at will onto a photonic platform, in our case, ion exchange waveguide (...

We simulate the dynamics of H2+ and HD+ by direct solution of the time-dependent Schroedinger equation for the electronic and nuclear motion for the interaction of intense femtosecond pulses. On these timescales the rotational motion, even for such light molecules, is frozen. Therefore it is a reasonable assumption that the nuclear alignment is fixed during the pulse interaction and that rotation can be neglected. In terms of vibrational relaxation, and since the nuclei are light, vibration will be important over femtosecond timescales. Although homonuclear diatomics are IR-inactive, in an intense field one can create vibrational excitation through continuum coupling. To show the effect of vibration, consider a first approximation in which the nuclei are infinitely massive so they maintain their positions at a fixed bond length of R=2 a.u., throughout the process.

We propose a control scheme for selecting populations of molecular rotational states by wave-packet interference. A series of coherent rotational wave packets is created by nonadiabatic rotational excitation of molecules using two strong femtosecond laser pulses. By adjusting the time delay between the two laser pulses, constructive or destructive interference among these wave packets enables the population to be enhanced or suppressed for a specific rotational state. The evolution of the rotational wave packet with selected populations produces interference patterns with controlled spatial symmetries. This method provides an approach to prepare a molecular ensemble with selected quantum-state distributions and controlled spatial distributions under field-free condition.

We present a comprehensive mathematical framework that integrates harmonic wave interference, fractal-holographic encoding, and a deterministic prime number generation scheme. First, we rigorously demonstrate how certain reciprocals of large integersexemplified by $1/999,999,998,000,000,001$-produce perfect harmonic sequences in their decimal expansion. These sequences concatenate integer ratios (e.g. 1/2, 2/3, 3/4, …) in a single number, with abrupt transitions at specific digits that resemble quantum jumps in a spectrum. By making minute shifts in the denominator (for example, comparing $999,999,998,000,000,001$ to $99,999,9989,000,000,01$), we show that the system's behavior changes from a smooth classical harmonic progression to a discretized, interference-like pattern-an analog of transitioning from classical to quantum computation. We then integrate a geometric prime pattern based on powers of 4 that generates primes in deterministic fashion, verified up to the 1999th prime researchgate.net

The space between the emitter and the absorber of an individual wave in the vacuum (photon, electron, neutron, etc.) is symmetrized by the hypothesis that the curvature of the wave fronts is the difference between the inverses of the distances to the emitter and the absorber. Then, on a sagittal plane, the so-defined circles are precisely a Poncelet’s bundle, orthogonal to the secant circles. The Fermat-Fresnel constraint on each actual route is that it does not delay more than a quarter of a period. It yields the maximum diameter of each Fermat’s spindle-shaped channel: \textbf{$\sqrt{3\lambda.a}$ }/ 2, where 2a is the distance between the absorber and the emitter, and λ is the wavelength. Let r be the radius of the physical apex, emitter, or absorber. It is seen from the mathematical apex at a Fermat’s angle α =  $\sqrt{\frac{3\lambda}{4a}}$, so at a distance ε = \textbf{\emph{r}}\textbf{. $\sqrt{\frac{4a}{3\lambda}}$.}. On astronomical distances, the individual character of the wave is no longer valid but is dominated by the collective interaction of the bosons sharing similar frequency and similar wave vector. So is the Hanbury Brown & Twiss grouping, which permits interferential Astronomy.

The dispersion characteristics and the field structure of axisymmetric modes channeled by a high-density pldsma inhomogeneity stretching along the external magnetic field are determined in the whistler range. The feasibility of matching a small antenna to the background plasma by means of plasma inhomogeneity is demonstrated theoretically and experimentally. The use ofinhomogeneous waveguides (which retard magnetic waves) in a magnetoactive plasma is of great interest for problems of channeled electromagnetic energy transfer. Such problems arise during the solution of very diverse physical problems, ranging from rf plasma heating in controll~ fusion facilities to excitation and propagation of whistling atmospherics (whistlers) in the ionosphere. Of particular interest are the potentialities associated with the formation of plasma waveguides by the radiation field of an antenna. For instance, Stenzel [1] observed the formation of a density duct in the background plasma and capture of vibration radiation into it. A simplified theoretical model of such capture was given by Karpman and Shagalov . Elsewhere [3] we observed ionization self-channeling of whistlers. The possibility of a vibrator antenna self-tuning to resonance as a result of the vibrator field forming a plasma inhomogeneity with the required density was demonstrated in 14]. In this study we determine the dispersion characteristics and the structure of the field of axisymmetric waves, channeled by a high-density plasma inhomogencity stretching along the external field in the whistler-frequency range and calculate the increasc of resistance of the whistler emission by the vibrator as a function of the plasma parameters in the inhomogeneity. Theoretically and experimentally we demonstrate that matching of a small vibrator is possible because the great!y retarded whistlers it excited of the inhomogeneity are smoothly transformed into natural waves of the background plasma.

We achieve 0.5-W and 110-fs pulses from a diodepumped mode locked Cr:LiSAF laser, pumped by a 1200times diffraction-limited 0.9-cm-wide 15-W diode-laser array. Pulses as short as 50 fs at 0.34 W are obtained, and a continous-wave output power of 1.42 W. These high-power results are based on an optimized mode-matching technique for good pump beam to cavity mode overlap, combined with a specialized crystal size and cooling geometry. A semiconductor saturable absorber mirror (SESAM) with low insertion loss is used to start and stabilize the mode locking. Using this device has the advantage that the mode locking dynamics are decoupled from the cavity layout, which is important for the design of the high-power resonator. In comparison to this high-power approach, we obtain 125-mW, 60-fs, and 105-mW, 45-fs pulses from a standard diode-pumped femtosecond Cr:LiSAF laser using two 12-times diffractionlimited high-brightness 0.5-W, 100-µm pump diodes.

We build a time series of single photons with quantum chaos statistics, using a version of the Grangier anti-correlation experiment. The criteria utilized to determine the presence of quantum chaos is the frame of the Fano factor and the power spectrum. We also show that photons with chaotic statistics are in a balanced superposition of photons with both wave-like and particle like behaviors. To support the presence of quantum chaos, we study both Shannon’s entropy, and the complexity of single photons time series.

We provide a theoretical scheme for realizing a Hadamard and a quantum controlled-NOT logic gates operations in the anti-Jaynes-Cummings interaction process. Standard Hadamard operation for a specified initial atomic state is achieved by setting a specific sum frequency and photon number in the anti-Jaynes-Cummings qubit state transition operation with the interaction component of the anti-Jaynes-Cummings Hamiltonian generating the state transitions. The quantum controlled-NOT logic gate is realised when a single atomic qubit defined in a two-dimensional Hilbert space is the control qubit and two non-degenerate and orthogonal polarised cavities defined in a two-dimensional Hilbert space make the target qubit. With precise choice of interaction time in the anti-Jaynes-Cummings qubit state transition operations defined in the anti-Jaynes-Cummings sub-space spanned by normalised but non-orthogonal basic qubit state vectors, we obtain ideal unit probabilities of success in the quantum controlled-NOT operations.

We present a method for dealing with quantum systems coupled to a structured reservoir with any density of modes and with more than one excitation. We apply the method to a two-level atom coupled to the edge of a photonic band gap and a defect mode. Results pertaining to this system, provide the solution to the problem of two photons in the reservoir and possible generalization is discussed.

We review basic quantum electrodynamics and quantum optics aspects in microstructures that exhibit a gap in the spectrum of the electromagnetic radiation they support, known as photonic crystals. After a brief sketch of the properties of such materials we discuss the behaviour of few-level atoms or collections thereof with transition frequencies inside and in the vicinity of the gap. The discussion is cast in terms of a unified formalism which facilitates the comparison with standard cavity-atom physics.

Despite the relative simplicity of the traditional Hong–Ou–Mandel (HOM) interferometer setup, it is of fundamental interest in various quantum optics applications and quantum information technologies. In this article, multi-photon interference using the original HOM interferometer setup is analyzed. More specifically, for any photon number state with Gaussian spectral distribution entering the beam splitter, the general analytical solution is calculated. The result is then used to study the coincident probability for coherent sources (laser) and squeezed coherent state. We also look into the potential benefits of implementing the squeezed coherent state in discrete-variable Measurement-Device-Independent Quantum Key Distribution and find that by optimizing the squeezing parameter, the error rate can be significantly reduced. This in turn also enhances the secret key rate performance over the coherent state.

We consider the use of space-filling curves (SFC) in scanning control parameters for quantum chemical systems. First we show that a formally exact SFC must be singular in the control parameters, but a finite discrete generalization can be used with no problem. We then make general observations about the relevance of SFCs in preference to linear scans of the parameters. Finally we present a simple magnetic field example relevant in NMR and show from the calculated autocorrelations that a SFC Peano-Hilbert curve gives a smoother sequence than a linear scan.

We study and extend the semidefinite programming (SDP) hierarchies introduced in [Phys. Rev. Lett. 115, 020501] for the characterization of the statistical correlations arising from finite dimensional quantum systems. First, we introduce the dimension-constrained noncommutative polynomial optimization (NPO) paradigm, where a number of polynomial inequalities are defined and optimization is conducted over all feasible operator representations of bounded dimensionality. Important problems in device independent and semi-device independent quantum information science can be formulated (or almost formulated) in this framework. We present effective SDP hierarchies to attack the general dimension-constrained NPO problem (and related ones) and prove their asymptotic convergence. To illustrate the power of these relaxations, we use them to derive new dimension witnesses for temporal and Bell-type correlation scenarios, and also to bound the probability of success of quantum random access codes.

Product Description Periodically Poled Stoichiometric Lithium Tantalate chips offer a cost effective method for visible and mid-infrared frequency generation. A multi-step lithographic and electric field poling process effects a permanent change in the non-linear properties of Lithium Tantalate. Using quasi-phase matching, with a selection of periods, crystal widths and lengths, PPSLT offers users an alternative to dedicated frequency conversion crystals. Applications • RGB laser generation • IR/Mid-IR laser generation • Visible Light Generation • 1st order or higher order wavelength conversion • Remote Sensing

In the recent years a significant amount of efforts are focused on the development of single-frequency nanosecond and sub-nscompact lasers providing high energy (>1 mJ) and high average power(>1W ) simultaneously. Q-switched, single frequency and si gletransversemode lasers are essential for wide vari ty of applications [1] such as laser-induced breakdown sp ectroscopy, LIDARs, optical communications and lase r trapping or cooling. The spatial dimension of conve ntional solid state Q-switched lasers precludes pro ducing single frequencypulses with sub-nanosecondor few-ns duration. Although the short-cavity, passively Q-s witched microchip lasers allow oscillations in single longi tudinalmode and generation of ~1 ns pulses device s th ir applicability is limited due to the inherent non-sa tur ted losses in the absorber, which impose consid erable limitation over achieving average power levels (~10 0mW) and poor ability for synchronization of the la ser pulses with external elec...

In this paper we study the quantum phase properties of "nonlinear coherent states" and "solvable quantum systems with discrete spectra" using the Pegg-Barnett formalism in a unified approach. The presented procedure will then be applied to few special solvable quantum systems with known discrete spectrum as well as to some new classes of nonlinear oscillators with particular nonlinearity functions. Finally the associated phase distributions and their nonclasscial properties such as the squeezing in number and phase operators have been investigated, numerically.

Theoretical analysis of a suspended nanomechanical membrane subject to an optical driving field in an optomechanical cavity is presented, which is confirmed through numerical simulations. In the presence of an optical field between its mirrors, the high-finesse optomechanical resonator acts as an oscillator driven by a radiation pressure force. The periodic nature of the radiation pressure force makes the nano-mechanical membrane in the optomechanical system as a kicked harmonic oscillator. Mathematically the physical system displays a stochastic web map that helps to understand several properties of the kicked membrane in classical phase space. We find that our web map is area preserving and displays quasiperiodic symmetrical structures in phase space which we express as q-fold symmetry. It is shown that under appropriate control of certain parameters, namely the frequency ratio and the kicking strength, the dynamics of kicked membrane exhibits chaotic dynamics. We provide the stability analysis by means of Lyapunov exponent and survival probability.

Quantum memories allowing reversible transfer of quantum states between light and matter are central to quantum repeaters, quantum networks and linear optics quantum computing. Significant progress regarding the faithful transfer of quantum information has been reported in recent years. However, none of these demonstrations confirm that the re-emitted photons remain suitable for two-photon interference measurements, such as C-NOT gates and Bell-state measurements, which constitute another key ingredient for all aforementioned applications. Here, using pairs of laser pulses at the single-photon level, we demonstrate two-photon interference and Bell-state measurements after either none, one or both pulses have been reversibly mapped to separate thulium-doped lithium niobate waveguides. As the interference is always near the theoretical maximum, we conclude that our solid-state quantum memories, in addition to faithfully mapping quantum information, also preserve the entire photonic wavefunction. Hence, our memories are generally suitable for future applications of quantum information processing that require two-photon interference.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Quantum memories allowing reversible transfer of quantum states between light and matter are central to quantum repeaters, quantum networks and linear optics quantum computing. Significant progress regarding the faithful transfer of quantum information has been reported in recent years. However, none of these demonstrations confirm that the re-emitted photons remain suitable for two-photon interference measurements, such as C-NOT gates and Bell-state measurements, which constitute another key ingredient for all aforementioned applications. Here, using pairs of laser pulses at the single-photon level, we demonstrate two-photon interference and Bell-state measurements after either none, one or both pulses have been reversibly mapped to separate thulium-doped lithium niobate waveguides. As the interference is always near the theoretical maximum, we conclude that our solid-state quantum memories, in addition to faithfully mapping quantum information, also preserve the entire photonic wavefunction. Hence, our memories are generally suitable for future applications of quantum information processing that require two-photon interference.

The reversible transfer of quantum states of light in and out of matter constitutes an important building block for future applications of quantum communication: it allows synchronizing quantum information 1 , and enables one to build quantum repeaters 2 and quantum networks 3 . Much effort has been devoted worldwide over the past years to develop memories suitable for the storage of quantum states 1 . Of central importance to this task is the preservation of entanglement, a quantum mechanical phenomenon whose counter-intuitive properties have occupied philosophers, physicists and computer scientists since the early days of quantum physics 4 . Here we report, for the first time, the reversible transfer of photonphoton entanglement into entanglement between a photon and collective atomic excitation in a solid-state device. Towards this end, we employ a thulium-doped lithium niobate waveguide in conjunction with a photon-echo quantum memory protocol 5 , and increase the spectral acceptance from the current maximum of 100 MHz 6 to 5 GHz. The entanglement-preserving nature of our storage device is assessed by comparing the amount of entanglement contained in the detected photon pairs before and after the reversible transfer, showing, within statistical error, a perfect mapping process. Our integrated, broadband quantum memory complements the family of robust, integrated lithium niobate devices 7 . It renders frequency matching of light with matter interfaces in advanced applications of quantum communication trivial and institutes several key properties in the quest to unleash the full potential of quantum communication. Quantum communication is founded on the encoding of information, generally referred to as quantum information, into quantum states of light 8 . The resulting applications of quantum physics at its fundamental level offer cryptographic security through quantum key distribution without relying on unproven mathematical assumptions 9 and allow for the disembodied transfer of quantum states between distant places by means of quantum teleportation 8, . Reversible mapping of quantum states between light and matter is central to advanced applications of quantum communication, e.g. quantum repeaters 2 and quantum networks 3 , in which matter

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.

We report new experiments on polarization squeezing using ultrashort photonic pulses in a single pass of a birefringent fiber. We measure what is to our knowledge a record squeezing of -6.8 ± 0.3 dB in optical fibers which when corrected for linear losses is -10.4 ± 0.8 dB. The measured polarization squeezing as a function of optical pulse energy, which spans a wide range from 3.5-178.8 pJ, shows a very good agreement with the quantum simulations and for the first time we see the experimental proof that Raman effects limit and reduce squeezing at high pulse energy.

Observables of quantum systems can posses either a discrete or a continuous spectrum. For example, upon measurements of the photon number of a light state, discrete outcomes will result whereas measurements of the light's quadrature amplitudes result in continuous outcomes. If one uses the continuous degree of freedom of a quantum system either for encoding, processing or detecting information, one enters the field of continuous variable (CV) quantum information processing. In this paper we review the basic principles of CV quantum information processing with main focus on recent developments in the field. We will be addressing the three main stages of a quantum informational system; the preparation stage where quantum information is encoded into CVs of coherent states and single photon states, the processing stage where CV information is manipulated to carry out a specified protocol and a detection stage where CV information is measured using homodyne detection or photon counting.

Applying a multiphoton-subtraction technique to two-color macroscopic squeezed vacuum state of light generated via high-gain parametric down conversion we conditionally prepare a new state of light: bright multi-mode low-noise twin beams. The obtained results demonstrate up to 8-fold suppression of noise in each beam while preserving and even moderately improving the nonclassical photon number correlations between the beams. The prepared low-noise macroscopic state, containing up to 2000 photons per mode, is not among the states achievable through nonlinear optical processes. The proposed technique substantially improves the usefulness of twin beams for quantum technologies.

Continuous variable quantum states of light are used in quantum information protocols and quantum metrology and known to degrade with loss and added noise. We were able to show the distribution of bright polarization squeezed quantum states of light through an urban free-space channel of 1.6 km length. To measure the squeezed states in this extreme environment, we utilize polarization encoding and a postselection protocol that is taking into account classical side information stemming from the distribution of transmission values. The successful distribution of continuous variable squeezed states is accentuated by a quantum state tomography, allowing for determining the purity of the state.

We demonstrate that the multipoles associated with the density matrix are truly observable quantities that can be unambiguously determined from intensity moments. Given their correct transformation properties, these multipoles are the natural variables to deal with a number of problems in the quantum domain. In the case of polarization, the moments are measured after the light has passed through two quarter-wave plates, one half-wave plate, and a polarizing beam splitter for specific values of the angles of the waveplates. For more general two-mode problems, equivalent measurements can be performed.