Properties of Squeezed-State Excitations

The photon distribution function of a discrete series of excitations of squeezed coherent states is given explicitly in terms of Hermite polynomials of two variables. The Wigner and the coherent-state quasiprobabilities are also presented in closed form through the Hermite polynomials and their limiting cases. Expectation values of photon numbers and their dispersion are calculated. Some three-dimensional plots of photon distributions for different squeezing parameters demonstrating oscillatory behaviour are given.Comment: Latex,35 pages,submitted to Quant.Semiclassical Op

On Bargmann Representations of Wigner Function

By using the localized character of canonical coherent states, we give a straightforward derivation of the Bargmann integral representation of Wigner function (W). A non-integral representation is presented in terms of a quadratic form V*FV, where F is a self-adjoint matrix whose entries are tabulated functions and V is a vector depending in a simple recursive way on the derivatives of the Bargmann function. Such a representation may be of use in numerical computations. We discuss a relation involving the geometry of Wigner function and the spacial uncertainty of the coherent state basis we use to represent it.Comment: accepted for publication in J. Phys. A: Math. and Theo

Quantum mechanical photon-count formula derived by entangled state representation

By introducing the thermo entangled state representation, we derived four new photocount distribution formulas for a given density operator of light field. It is shown that these new formulas, which is convenient to calculate the photocount, can be expressed as such integrations over Laguree-Gaussian function with characteristic function, Wigner function, Q-function, and P-function, respectively.Comment: 5 pages, no figur

Lorentz Beams

A new kind of tridimensional scalar optical beams is introduced. These beams are called Lorentz beams because the form of their transverse pattern in the source plane is the product of two independent Lorentz functions. Closed-form expression of free-space propagation under paraxial limit is derived and pseudo non-diffracting features pointed out. Moreover, as the slowly varying part of these fields fulfils the scalar paraxial wave equation, it follows that there exist also Lorentz-Gauss beams, i.e. beams obtained by multipying the original Lorentz beam to a Gaussian apodization function. Although the existence of Lorentz-Gauss beams can be shown by using two different and independent ways obtained recently from Kiselev [Opt. Spectr. 96, 4 (2004)] and Gutierrez-Vega et al. [JOSA A 22, 289-298, (2005)], here we have followed a third different approach, which makes use of Lie's group theory, and which possesses the merit to put into evidence the symmetries present in paraxial Optics.Comment: 11 pages, 1 figure, submitted to Journal of Optics

Wigner function evolution in self-Kerr Medium derived by Entangled state representation

By introducing the thermo entangled state representation, we convert the calculation of Wigner function (WF) of density operator to an overlap between "two pure" states in a two-mode enlarged Fock space. Furthermore, we derive a new WF evolution formula of any initial state in self-Kerr Medium with photon loss and find that the photon number distribution for any initial state is independent of the coupling factor with Kerr Medium, where the number state is not affected by the Kerr nonlinearity and evolves into a density operator of binomial distribution.Comment: 9 pages, 1 figur

Effect of the Microstructure of Copper Films on the Damping of Oscillating Quartz Resonators*

An electrochemical procedure is described which allows the preparation of copper films of various crystallinity. Impedance spectra recorded for copper loaded quartz resonators were analysed in terms oft he lumped-element circuit of the Butterworth-Van Dyke type to obtain their electrical and mechanical properties. Plots of the damping resistance versus film thickness indicate that the film's dissipation factor is significantly smaller in the case of disordered films with a finer crystallinity (10—100nm) than in the case of more ordered structures having a grain size between 600—1500nm. This observations states, that the finely structured copper phase behaves more rigid than the coarse material. The suggested explanation relates this effect to energy losses which occur during oscillation at the phase boundary of the grains by wearless internal friction. No contributions to the damping from surface roughness were observed for films thicker 0.5pm. Thus, the damping of the quartz oscillator caused by different degrees of surface roughness of the generated copper films was of secondary importance, compared with the effect of the crystallinity

Energy-Sensitive and "Classical-like" Distances Between Quantum States

We introduce the concept of the ``polarized'' distance, which distinguishes the orthogonal states with different energies. We also give new inequalities for the known Hilbert-Schmidt distance between neighbouring states and express this distance in terms of the quasiprobability distributions and the normally ordered moments. Besides, we discuss the distance problem in the framework of the recently proposed ``classical-like'' formulation of quantum mechanics, based on the symplectic tomography scheme. The examples of the Fock, coherent, ``Schroedinger cats,'' squeezed, phase, and thermal states are considered.Comment: 23 pages, LaTex, 2 eps figures, to appear in Physica Script

Non-classicality of photon added coherent and thermal radiations

Production and analysis of non-Gaussian radiation fields has evinced a lot of attention recently. Simplest way of generating such non-Gaussians is through adding (subtracting) photons to Gaussian fields. Interestingly, when photons are added to classical Gaussian fields, the resulting states exhibit {\em non-classicality}. Two important classical Gaussian radiation fields are coherent and thermal states. Here, we study the non-classical features of such states when photons are added to them. Non-classicality of these states shows up in the negativity of the Wigner function. We also work out the {\em entanglement potential}, a recently proposed measure of non-classicality for these states. Our analysis reveals that photon added coherent states are non-classical for all seed beam intensities; their non-classicality increases with the addition of more number of photons. Thermal state exhibits non-classicality at all temperatures, when a photon is added; lower the temperature, higher is their non-classicality.Comment: Version 2, minor revision; new references added, to appear in Eur. Phys. J. D, 6 pages, 10 figure ps files, RevTe

Excitability of lasers with integrated dispersive reflector

This paper is concerned with the phenomenon of excitability in semiconductor lasers consisting of a DFB section and a passive dispersive reflector (PDR). We assume that the PDR section contains a Bragg grating and (or) a passive Fabry Perot filter guaranteeing a dispersive reflection of the optical field. We investigate a single mode model for PDR lasers and derive conditions under which excitable behavior can be demonstrated. Especially, we show the existence of a threshold, that is, only perturbations above the threshold imply a large excursion from the steady state, and where the response is almost independent of the strength of the perturbation, moreover we establish the existence of a refractory period, i.e., if a second perturbation is applied before the refractory time has passed, then the system does not respond. Finally, we discuss the importance of excitability for the transmission of signals in communication networks