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arXiv:0801.2440 · Journal of Physics B Atomic Molecular and Optical Physics

Subluminal to superluminal propagation of an optical pulse in anf-deformed Bose–Einstein condensate

Zahra Haghshenasfard, M. H. Naderi, M. Soltanolkotabi

Published Aug 7, 2008• 8 citations
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Abstract

In this paper, we investigate the propagation of a weak optical probe pulse in an f-deformed Bose- Einstein condensate (BEC) of a gas with the -type three- level atoms in the electromagnetically induced transparency (EIT) regime. We use an f- deformed generalization of an effective two- level quantum model of the three- level configuration in which the Gardiner phonon operators for BEC are deformed by an operator- valued function, f(n), of the particle- number operator n. With making use of the quantum approach of the angular momentum theory we obtain the eigenvalues and eigenfunctions of the system up to first order approximation. We consider the collisions between the atoms as a special kind of f- deformation. The collision rate k is regarded as the deformation parameter and light propagation in the deformed BEC is analyzed. In particular, we show that the absorptive and dispersive properties of the deformed condensate can be controlled effectively by changing the deformation parameter k and the total number of atoms. We find that by increasing the value of k the group velocity of the probe pulse changes, through deformed condensate, from subluminal to superluminal.

DOI
10.1088/0953-4075/41/16/165501

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In this paper, we investigate the propagation of a weak optical probe pulse in an f-deformed Bose- Einstein condensate (BEC) of a gas with the -type three- level atoms in the electromagnetically induced transparency (EIT) regime. We use an f- deformed generalization of an effective two- level quantum model of the three- level configuration in which the Gardiner phonon operators for BEC are deformed by an operator- valued function, f(n), of the particle- number operator n. With making use of the quantum approach of the angular momentum theory we obtain the eigenvalues and eigenfunctions of the system up to first order approximation. We consider the collisions between the atoms as a special kind of f- deformation. The collision rate k is regarded as the deformation parameter and light propagation in the deformed BEC is analyzed. In particular, we show that the absorptive and dispersive properties of the deformed condensate can be controlled effectively by changing the deformation parameter k and the total number of atoms. We find that by increasing the value of k the group velocity of the probe pulse changes, through deformed condensate, from subluminal to superluminal.
Investigations are made for the possibility of using an f-deformed Bose–Einstein condensate (BEC) inside the resonator of a mode-locked laser to achieve tunable control of the repetition rate. Slow light propagation of the probe field through the f-deformed BEC may lead to a large observable increase in the cavity round-trip delay and, therefore, to a reduction in the effective repetition rate of the laser. Conversely, negative propagation velocity through the f-deformed BEC can lead to a decrease in the cavity round-trip and to an increase in the effective repetition rate. Simulations are presented using an f-deformed BEC of Λ-type three-level atoms beyond the rotating wave approximation. Collisions between the atoms are considered as a special kind of f-deformation where the collision rate κ is regarded as the deformation parameter. In particular, it is found that the repetition rate can be controlled effectively by changing the collision rate κ, the total number of atoms N and the parameter λ for the counter-rotating terms.
In this paper, we investigate the spectrum of light scattered from a Bose-Einstein condensate in the framework of -deformed boson.We use an -deformed quantum model in which the Gardiner's phonon operators for BEC are deformed by an operator-valued function,, of the particle-number operator n .We consider the collisions between the atoms as a special kind of -deformation.The collision rateκ is regarded as the deformation parameter and the spectrum of light scattered from the deformed BEC is analyzed.In particular, we find that with increasing the values of deformation parameters κ and N 1 = η ( , total number of condensate atoms) the scattering spectrum shows deviation from the spectrum associated with nondeformed Bose-Einstein condensate.
In this paper, we investigate the spontaneous emission of an f -deformed Bose–Einstein condensate of a gas with N identical two-level atoms immersed in a single-mode ideal cavity with s atoms initially excited. We apply an f -deformed quantum model in which Gardiner's phonon operators are deformed by an operator-valued function of the particle number operator . We consider the collisions between the atoms as a special kind of f -deformation where the collision rate κ is regarded as a corresponding deformation parameter. The time evolution of the expectation value of the atomic inversion is presented, the phenomenon of collective collapses and revivals is shown and the effects of deformation on the cooperative behaviour of the system are discussed.
We study the dispersion and absorption spectra of a weak probe in a $\ensuremath{\Lambda}$-type three-level atomic system with closely ground sublevels driven by a strong field and damped by a broadband squeezed vacuum. We analyze the interplay between the spontaneous generated coherence and the squeezed field on the susceptibility of the atomic system. We find that by varying the intensity of the squeezed field the group velocity of a weak pulse can change from subluminal to superluminal. In addition we exploit the fact that the properties of the atomic medium can be dramatically modified by controlling the relative phase between the driving field and the squeezed field, allowing us to manipulate the group velocity at which light propagates. The physical origin of this phenomenon corresponds to a transfer of the atomic coherence from electromagnetically induced transparency to electromagnetically induced absorption. Besides, this phenomenon is achieved under nearly transparency conditions and with negligible distortion of the propagation pulse.
The propagation of a weak probe field in a four-level N-type quantum system in the presence of spontaneously generated coherence (SGC) is theoretically investigated. The optical properties of the system are studied and it is shown that the group velocity of light pulse can be controlled by relative phase of applied fields. By changing the relative phase of applied fields, the group velocity of light pulse changes from transparent subluminal to the transparent superluminal light propagation. Thus, the phase-controlled absorption-free superluminal light propagation is obtained without applying an incoherent laser fields to the system. The propagation of a weak probe light pulse is studied by solving the Maxwell's wave equation on numerical grid in space and time. Moreover, we study the third order self- and cross-Kerr susceptibility of probe field and calculate the nonlinear cross-phase shift for different values of intensity of applied fields. In addition, we take into account the effect of Doppler broadening on the light pulse propagation and it is found that a suitable choice of laser propagation directions allows us to preserve our results even in the presence of Doppler effect. It is demonstrated that by increasing the Doppler width of distribution to the room temperature, the dispersion changes from transparent subluminal to transparent superluminal light propagation which is our major motivation for this work.