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Journal of Physics A Mathematical and General

New features of the atomic Wehrl entropy and its density in multi-quanta two-level system

A.‐S. F. Obada, S. Abdel‐Khalek

Published Jun 10, 2004• 60 citations
Publisher

Abstract

This contribution describes new features of the atomic Wehrl entropy in a multi-quanta two-level system in the presence of the Kerr medium. A definition of the atomic Wehrl entropy is presented for this system, based on the atomic Q -function as information measurement about the atomic phase space. The influence of the nonlinear interaction of the Kerr medium, Stark shift, one and two-photon processes and the detuning parameters on the properties of the atomic Wehrl entropy is examined. The atomic Wehrl entropy gives equivalent results to the von Neumann entropy.

DOI
10.1088/0305-4470/37/25/010

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This contribution describes new features of the atomic Wehrl entropy in a multi-quanta two-level system in the presence of the Kerr medium. A definition of the atomic Wehrl entropy is presented for this system, based on the atomic Q -function as information measurement about the atomic phase space. The influence of the nonlinear interaction of the Kerr medium, Stark shift, one and two-photon processes and the detuning parameters on the properties of the atomic Wehrl entropy is examined. The atomic Wehrl entropy gives equivalent results to the von Neumann entropy.
In the language of quantum information theory we study the entropy squeezing of a two-level atom in a Kerr-like medium. A definition of squeezing is presented for this system, based on information theory. The utility of the definition is illustrated by examining the entropy squeezing of a two-level atom with a Kerr-like medium. The influence of the non-linear interaction of the Kerr medium, the atomic coherence and the detuning parameter on the properties of the entropy and squeezing of the atomic variables is examined.
From a quantum information point of view we study the entropy squeezing of a two-level atom interacting with two modes with intensity-dependent coupling. The Hamiltonian we consider consists of all acceptable forms of nonlinearities. A definition of squeezing is presented for this system, based on information theory. The utility of the definition is illustrated by examining squeezing in the information entropy of a two-level atom in the presence of a nonlinear medium. We examine the influence of the nonlinear interaction, the atomic coherence and the detuning parameter on the properties of the entropy and squeezing of the atomic variables. It is shown that features of the quantum entropy are influenced significantly by the kinds of intensity-dependent atom-field coupling and the nonlinearities of the two-mode fields.
In this study, we use the quantum entropy to measure the degree of entanglement in the time development of the two-level particle (atom or ion). The influence of atomic coherence on the evolution of the field quantum entropy and the entanglement of the atom-field in the two-photon process, taking into account the level shifts produced by the Stark effect with an additional Kerr-like medium for one mode, are examined. The exact results are employed to perform a careful investigation of the temporal evolution of the entropy. It is shown that the evolution of the field entropy is very sensitive to the relative phase of the particle and field. The effect of both the Stark shift and the presence of a Kerr-like medium on the entropy is analyzed. The results show that the effect of the Kerr-like medium and the Stark shift changes the quasiperiod of the field entropy evolution and the entanglement between the particle and the field. The general conclusions reached are illustrated by numerical results.
In this framework, the effect of a Kerr-like medium and the coupling function dependent on the number of photons operator on the interaction between a two-level atom and a non-linear field is studied. A relation between the Kerr-like medium parameter and the field-atom coupling parameter is used to obtain a simplified formula for Rabi frequency. The wave function of the proposed model is obtained, followed by the derivation of the phase distribution and from which the wehrl entropy formula is calculated. The effect of the initial state and the non-linear func?tion dependent on the number of photons operator and the Kerr-like medium on entanglement is calculated through the Wehrl entropy formula, wehrl distribution and the behaviour of photons by studying the correlation function. The entangle?ment decreases when the function dependent on the number of photons operator is taken into account, while the entanglement gradually improves when the squeezed state is considered, and the entanglement decreases significantly when considering the Kerr medium. An oscillatory distribution is formed between the classical and non-classical in the coherent state. The non-classical distribution disappears when considering the squeezed state and the Kerr-like medium.
The interaction between a ♢\diamondsuit♢-type four-level atom and a single-mode field in the presence of Kerr medium with intensity-dependent coupling involving multi-photon processes has been studied. Using the generalized (nonlinear) Jaynes-Cummings model, the exact analytical solution of the wave function for the considered system under particular condition, has been obtained when the atom is initially excited to the topmost level and the field is in a coherent state. Some physical properties of the atom-field entangled state such as linear entropy showing the entanglement degree, Mandel parameter, mean photon number and normal squeezing of the resultant state have been calculated. The effects of Kerr medium, detuning and the intensity-dependent coupling on the temporal behavior of the latter mentioned nonclassical properties have been investigated. It is shown that by appropriately choosing the evolved parameters in the interaction process, each of the above nonclassicality features, which are of special interest in quantum optics as well as quantum information processing, can be revealed.
Abstract This paper presents new results on some aspects of the properties of the entropy squeezing in the time development of a degenerate two-photon of a single-mode interacting with a two-level system with a nonlinear medium. A general analytic expression for the density matrix is obtained on the basis of a Hamiltonian generalized in that it includes nonlinear effects and Stark shifts, by means of which we identify and numerically demonstrate the region of parameters where significantly large squeezing can be obtained. The influence of various parameters on the entropy squeezing are explored. It is shown that features of the entropy squeezing were influenced significantly by changing the nonlinear medium, Stark shift and the detuning. The results show that, certain amounts of the nonlinear effect yield the superstructure of atomic Rabi oscillation and changes the quasiperiod of the entropy evolution and atomic inversion.