Photon-number distributions of twin beams generated in spontaneous parametric down-conversion and measured by an intensified CCD camera

The measurement of photon-number statistics of fields composed of photon pairs, generated in spontaneous parametric down-conversion and detected by an intensified CCD camera is described. Final quantum detection efficiencies, electronic noises, finite numbers of detector pixels, transverse intensity spatial profiles of the detected beams as well as losses of single photons from a pair are taken into account in a developed general theory of photon-number detection. The measured data provided by an iCCD camera with single-photon detection sensitivity are analyzed along the developed theory. Joint signal-idler photon-number distributions are recovered using the reconstruction method based on the principle of maximum likelihood. The range of applicability of the method is discussed. The reconstructed joint signal-idler photon-number distribution is compared with that obtained by a method that uses superposition of signal and noise and minimizes photoelectron entropy. Statistics of the reconstructed fields are identified to be multi-mode Gaussian. Elements of the measured as well as the reconstructed joint signal-idler photon-number distributions violate classical inequalities. Sub-shot-noise correlations in the difference of the signal and idler photon numbers as well as partial suppression of odd elements in the distribution of the sum of signal and idler photon numbers are observed.Comment: 14 pages, 14 figure

Surface spontaneous parametric down-conversion

Surface spontaneous parametric down-conversion is predicted as a consequence of continuity requirements for electric- and magnetic-field amplitudes at a discontinuity of chi2 nonlinearity. A generalization of the usual two-photon spectral amplitude is suggested to describe this effect. Examples of nonlinear layered structures and periodically-poled nonlinear crystals show that surface contributions to spontaneous down-conversion can be important.Comment: 4 pages, 3 figure

Absolute detector calibration using twin beams

A method for the determination of absolute quantum detection efficiency is suggested based on the measurement of photocount statistics of twin beams. The measured histograms of joint signal-idler photocount statistics allow to eliminate an additional noise superimposed on an ideal calibration field composed of only photon pairs. This makes the method superior above other approaches presently used. Twin beams are described using a paired variant of quantum superposition of signal and noise.Comment: 3 pages, 2 figure

Emission of photon pairs at discontinuities of nonlinearity in spontaneous parametric down-conversion

In order to fulfil the continuity requirements for electric- and magnetic-field amplitudes at discontinuities of chi2 nonlinearity additional photon pairs have to be emitted in the area of discontinuity. Generalized two-photon spectral amplitudes can be used to describe properties of photon pairs generated in this process that we call surface spontaneous parametric down-conversion. The spectral structure of such photon pairs is similar to that derived for photon pairs generated in the volume. Surface and volume contributions to spontaneous down-conversion can be comparable as an example of nonlinear layered structures shows.Comment: 11 pages, 8 figure

Spatial and spectral properties of the pulsed second-harmonic generation in a PP-KTP waveguide

Spatial and spectral properties of the pulsed second harmonic generation in a periodically-poled KTP waveguide exploiting simultaneously the first, second, and third harmonics of periodic nonlinear modulation are analyzed. Experimental results are interpreted using a model based on finite elements method. Correlations between spatial and spectral properties of the fundamental and second-harmonic fields are revealed. Individual nonlinear processes can be exploited combining spatial and spectral filtering. Also the influence of waveguide parameters to the second-harmonic spectra is addressed.Comment: 13 pages, 8 figure

Quantum identification system

A secure quantum identification system combining a classical identification procedure and quantum key distribution is proposed. Each identification sequence is always used just once and new sequences are ``refuelled'' from a shared provably secret key transferred through the quantum channel. Two identification protocols are devised. The first protocol can be applied when legitimate users have an unjammable public channel at their disposal. The deception probability is derived for the case of a noisy quantum channel. The second protocol employs unconditionally secure authentication of information sent over the public channel, and thus it can be applied even in the case when an adversary is allowed to modify public communications. An experimental realization of a quantum identification system is described.Comment: RevTeX, 4 postscript figures, 9 pages, submitted to Physical Review

Squeezed-light generation in a nonlinear planar waveguide with a periodic corrugation

Two-mode nonlinear interaction (second-harmonic and second-subharmonic generation) in a planar waveguide with a small periodic corrugation at the surface is studied. Scattering of the interacting fields on the corrugation leads to constructive interference that enhances the nonlinear process provided that all the interactions are phase matched. Conditions for the overall phase matching are found. Compared with a perfectly quasi-phase-matched waveguide, better values of squeezing as well as higher intensities are reached under these conditions. Procedure for finding optimum values of parameters for squeezed-light generation is described.Comment: 14 pages, 14 figure

Sub-Poissonian behaviour in the second harmonic generation

Abstract. A special class of quantum solutions of the second harmonic generation process exhibiting time-stable sub-Poissonian behaviour with Fano factor F ≈ 0.83 is numerically analysed. A theoretical prediction of that specific Fano number and an explanation of the extraordinary time stability of the sub-Poissonian behaviour is given using the semiclassical method of classical trajectories. Keywords: Photon statistics, sub-Poissonian statistics, Fano factor, second harmonic generation (SHG) Much experimental and theoretical attention has been devoted to the second harmonic generation (SHG) process since the first successful SHG by Franken in 1961 [1]. This process represents a special case of the processes described by the interaction Hamiltonian where a 1 and a 2 denote annihilation operators of the fundamental and second harmonic modes and g is a nonlinear coupling parameter. Unfortunately, no exact solution of quantum dynamics described by (1) can be found and many analytical approximations or numerical methods have to be used for describing the conversion efficiency, quantum noise statistics and other characteristics of the process An important noise parameter of photon statistics is the variance of photon number Var(n). If it is smaller than the mean photon number, i.e. Var(n) < n we call such light sub-Poissonian and it represents an example of non-classical light. In experiments, the Fano factor F = Var(n) n is often used for the description of the photon statistics. Apparently, the light is sub-Poissonian when F < 1. Such light has been generated and observed in many laboratories For coherent inputs α 1 = r 1 exp(iφ 1 ) and α 2 = r 2 exp(iφ 2 ), the short-time approximation (gt 1) gives the well known results (see, e.g., [6]) where the initial phase difference θ = 2φ 1 − φ 2 decides whether the process ω + ω → 2ω or the reversed process is realized and whether sub-Poissonian or super-Poissonian light is generated in the first moment of the interaction. In a spontaneous SHG process (α 2 = 0) sub-Poissonian light is generated as well and it holds that [6] whereas in a process (α 1 = 0) no sub-Poissonian light is generated (F 1,2 > 1) and only quadrature-squeezed light can be observed. For long interaction (i.e. the condition gt 1 is not fulfilled) no analytical predictions exist and numerical methods must be applied. We have used a well known method of diagonalization of the Hamiltonian used originally i