We perform a reconstruction of the polarization sector of the density matrix of an intense polarization squeezed beam starting from a complete set of Stokes measurements. By using an appropriate quasidistribution, we map this onto the Poincaré space providing a full quantum mechanical characterization of the measured polarization state.

The distribution of entangled states between distant parties in an optical network is crucial for the successful implementation of various quantum communication protocols such as quantum cryptography, teleportation and dense coding [1,2,3]. However, owing to the unavoidable loss in any real optical channel, the distribution of loss-intolerant entangled states is inevitably inflicted by decoherence, which causes a degradation of the transmitted entanglement. To combat the decoherence, entanglement distillation, which is the process of extracting a small set of highly entangled states from a large set of less entangled states, can be used [4,5,6,7,8,9,10,11,12,13,14]. Here we report on the mesoscopic distillation of deterministically prepared entangled light pulses that have undergone non-Gaussian noise. The entangled light pulses [15,16,17] Entanglement distillation has been experimentally demonstrated for spin 1/2 (or qubit)

We report on a novel and efficient source of polarization squeezing using a single pass through an optical fiber. Simply passing this Kerr squeezed beam through a carefully aligned λ/2 waveplate and splitting it on a polarization beam splitter, we find polarization squeezing of up to 5.1 ± 0.3 dB. The experimental setup allows for the direct measurement of the squeezing angle.c 2018 Optical Society of America OCIS codes: 190.3270, 190.4370, 270.5290, 270.6570. The budding field of quantum information holds promise to revolutionize communication. In particular the field of quantum information with continuous variables has received much attention in the last decades with the realization, for instance, of quantum teleportation, quantum cryptography and dense coding.1 Most of these protocols require the use of squeezed (or entangled) states of light that are generally detected using a strong local oscillator, which makes the scalability of quantum networks difficult. Recently, polarization squeezing has attracted much attention 2-6 as it can be measured in direct detection, 7 making it especially attractive for cryptography and other quantum communication applications. Furthermore the flucuations of the polarization variables can be mapped onto the collective fluctuations of an atomic ensemble, paving the way to quantum memory.8 To date polarization squeezing has been achieved using the nonlinear interactions in Optical Parametric Amplifiers, 4 optical fibers 5 and atomic media. 6In this paper we present the results of a novel and efficient method of bright pulse polarization squeezing generation using the Kerr effect in an optical fiber. This setup is greatly simplified relative to other schemes and leads to high squeezing levels. Further, this method enables us to completely characterize all quadratures of the state exiting an optical fiber. In particular we measured the angle by which the squeezed uncertainty region has been rotated by the nonlinear Kerr effect.It has been known for a long time that the optical Kerr effect in glass fiber can generate quadrature squeezing. This third order nonlinear effect (χ 3 ), also refered to as Self Phase Modulation produces an intensity dependent change in the refractive index. The squeezing generation can be understood by a single mode picture represented in Fig. 1(a): since different amplitudes experience different rotations in phase space, the fluctuation circle (corresponding to shot noise) of the input field is transformed into an ellipse. The squeezed quadrature is rotated by the angle θ sq relative the amplitude quadrature. Since the Kerr effect conserves photon number, the amplitude fluctuations remain at the shot noise level preventing direct detection of the squeezing.Polarization squeezing overcomes this problem. It can be generated by overlapping two quadrature squeezed beams produced in the two orthogonal polarization modes of the fiber, visualized byâ x andâ y in Fig. 1(b). This setup, seen in Fig. 2, is similar to our previous experiment producing polariza...

We investigate polarisation squeezing of ultrashort pulses in optical fibre, over a wide range of input energies and fibre lengths. Comparisons are made between experimental data and quantum dynamical simulations, to find good quantitative agreement. The numerical calculations, performed using both truncated Wigner and exact +P phase-space methods, include nonlinear and stochastic Raman effects, through coupling to phonons variables. The simulations reveal that excess phase noise, such as from depolarising GAWBS, affects squeezing at low input energies, while Raman effects cause a marked deterioration of squeezing at higher energies and longer fibre lengths. The optimum fibre length for maximum squeezing is also calculated.

We report on the generation of polarization squeezing of intense, short light pulses using an asymmetric fiber Sagnac interferometer. The Kerr nonlinearity of the fiber is exploited to produce independent amplitude squeezed pulses. The polarization squeezing properties of spatially overlapped amplitude squeezed and coherent states are discussed. The experimental results for a single amplitude squeezed beam are compared to the case of two phase-matched, spatially overlapped amplitude squeezed pulses. For the latter, noise variances of -3.4 dB below shot noise in theŜ0 and theŜ1 and of -2.8 dB in theŜ2 Stokes parameters were observed, which is comparable to the input squeezing magnitude. Polarization squeezing, that is squeezing relative to a corresponding polarization minimum uncertainty state, was generated inŜ1.

We report new experiments that test quantum dynamical predictions of polarization squeezing for ultrashort photonic pulses in a birefringent fiber, including all relevant dissipative effects. This exponentially complex many-body problem is solved by means of a stochastic phase-space method. The squeezing is calculated and compared to experimental data, resulting in excellent quantitative agreement. From the simulations, we identify the physical limits to quantum noise reduction in optical fibers. The research represents a significant experimental test of first-principles time-domain quantum dynamics in a onedimensional interacting Bose gas coupled to dissipative reservoirs. DOI: 10.1103/PhysRevLett.97.023606 PACS numbers: 42.50.Lc, 42.50.Dv, 42.65.Dr, 42.81.Dp The nonlinear optical response of standard communications fiber provides a straightforward and robust method [1] for squeezing the quantum noise always present in laser light to below the vacuum noise level. This feature allows us to design quantum dynamical experiments [2,3] operating in a very nonclassical regime where highly entangled states can be readily produced, even in many-body regimes involving 10 8 interacting particles. The squeezing is sensitive to photon-photon interactions, as well as to additional dissipative and thermal effects [4]. Such complications have affected all prior experiments and have so far prevented quantitative agreement between theory and experiment.Here we report on quantitative comparisons of firstprinciples simulations with experimental measurements on the propagation of quantum states in optical fiber. The excellent agreement, over a wide range of initial conditions, is unprecedented for direct predictions from ab initio treatments of many-body quantum time evolution. The approach we use has potential applications in many other areas of science, especially to dynamical experiments with ultracold atoms and nanotechnology.Photons in a nonlinear fiber are an implementation of the famous one-dimensional attractive Bose-gas model [5]. Fiber squeezing experiments thus provide a substantial opportunity to carry out an experimental test of the predictions of many-body quantum mechanics for dynamical time evolution. Such a test requires the same ingredients as did Galileo's famous tests of classical dynamics using an inclined plane [6]: one needs a known initial condition, a well-defined cause of dynamical evolution, and accurate measurements. All of these essential features are present in our experiments. The initial condition is a coherent [7] photonic state provided by a well-stabilized pulsed laser. The Kerr nonlinearity in silica fiber corresponds to a localized (delta-function) interaction between the photons [8]. Quantum-limited phase-sensitive measurements have been developed in optics that detect quantum fluctuations at well below the vacuum noise level [9,10].Even though the simplest model of a 1D interacting Bose gas has exactly soluble energy eigenvalues, the many-body initial-value problem still remains intractab...

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.

We show theoretically and experimentally that single copy distillation of squeezing from continuous variable non-Gaussian states is possible using linear optics and conditional homodyne detection. A specific non-Gaussian noise source, corresponding to a random linear displacement, is investigated. Conditioning the signal on a tap measurement, we observe probabilistic recovery of squeezing.