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Physical Review A

Effect of the dynamic Stark shift on dipole squeezing in two-photon processes

Tahira Nasreen, M. S. K. Razmi

Published Oct 1, 1992• 19 citations
Publisher

Abstract

Atomic-dipole squeezing in the presence of the Stark shift in two-photon Jaynes-Cummings model for an atom initially prepared in a coherent superposition of states, interacting with the coherent- or squeezed-vacuum-state field, is studied. Closed expressions for dispersive and absorptive components of the dipole for the coherent-field input under the large-n\ifmmode\bar\else\textasciimacron\fi{} approximation are derived. It is shown that atomic-dipole squeezing is sensitive to both the phase of the initial field and the relative phase between the two atomic levels. Our results show that, for certain choices of these phases, permanent dipole squeezing can be obtained.

DOI
10.1103/physreva.46.4161

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International Journal of Modern Physics B•Aug 15, 1994•1 citation
Atomic-dipole squeezing in the presence of the Stark shift in two-photon Jaynes-Cummings model for an atom initially prepared in a coherent superposition of states, interacting with the coherent- or squeezed-vacuum-state field, is studied. Closed expressions for dispersive and absorptive components of the dipole for the coherent-field input under the large-n\ifmmode\bar\else\textasciimacron\fi{} approximation are derived. It is shown that atomic-dipole squeezing is sensitive to both the phase of the initial field and the relative phase between the two atomic levels. Our results show that, for certain choices of these phases, permanent dipole squeezing can be obtained.
In this thesis, we investigate the effect of the dynamical Stark shift on the quantum electrodynamics of an atom undergoing two-photon transitions, interacting with a quantized radiation field in an ideal cavity. To begin with, we discuss the dynamics of the electromagnetic field and the atom in the presence of the Stark shift. We derive closed expressions for the second-order coherence function, quadrature variances, atomic population inversion and dipole squeezing under the approximation of a large initial photon number and coherent or squeezed field input. We show that for an atom initially in the ground state, the inclusion of Stark shift reduces the field squeezing as well as the antibunching. Both the population inversion and the dipole squeezing exhibit phase sensitivity in the presence of Stark shift and for a particular choice of the relative phase of the two atomic levels "trapping" occurs in a two-level atom and the dipole is modified in such a way that it is permanently squeezed. We then discuss the effect of the stark shift on the emission spectrum of an atom and the cavity field spectrum. The inclusion of Stark shift results in asymmetric vacuum field Rabi splitting. We also study the dynamics of the combined atom-field wave function in the presence of the Stark shift and show that both the electromagnetic field and the atom periodically evolve to pure states which are radically different from those in the absence of the Stark shift. Finally, we study the nondegenerate two-photon Jaynes-Cummings model (NTPJCM) in the presence of the Stark shift and show that the dynamics of the NTPJCM in the presence of Stark shift is qualitatively different from the case of the absence of the Stark shift and radically different from the case of degenerate two-photon JCM in the presence of Stark shift.
The atomic dipole squeezing and the emission spectra in a nondegenerate two-photon Jaynes–Cummings model in the presence of Stark shift for various field inputs are studied. The percentage duration of the atomic dipole squeezing is greatly enhanced by the inclusion of the Stark shift. The emission spectra show an asymmetric central two-peak structure that is quite different from that in the absence of the Stark shift. When the fields are initially in the coherent state, asymmetric coherent sidebands emerge. The effect of atomic coherence on dipole squeezing and the emission spectrum have also been incorporated
The problem of a single atom making two-photon transitions in the presence of a cavity field that is initially in the general squeezed state or squeezed vacuum state is studied. Closed expressions for the atomic inversion, the second-order coherence function, and the quadrature variances are derived under the assumption of a large initial average photon number and a squeezed field input. The effects of Stark shift on these quantities are analyzed and discussed. We see collapses and revivals of atomic inversion and the second-order coherence function with a general squeezed input, but none are apparent when the input is in the squeezed vacuum state. Perodic revivals of squeezing are seen.
Two-mode quantized electromagnetic fields can be entangled and admit a large number of coherent states. In this paper, we consider a two-mode system that consists of a two-level atom interacting with a two-mode quantized electromagnetic field, which is initially prepared in an entangled two-mode coherent state, via a nondegenerate two-photon process in a lossless cavity. We study the quantum fluctuations in the two-mode system and investigate in detail the effects of detuning, Stark shift and atomic coherence on atomic dipole squeezing (ADS). We show that ADS strongly depends on the atomic coherence. It is found that the stronger the correlations between the two modes are involved, the more the ADS could be generated. The detuning or Stark shift has a destructive effect on ADS, but the combined effect of the detuning and Stark shift may lead to a regular, periodical and strong ADS pattern.
Dipole squeezing of the atom in the presence of another atom is investigated for the one-photon and two-photon transition mechanism with the initial atoms in the two-atom squeezed state and the field in a vacuum, a coherent, or a squeezed state. For a vacuum input, the degree of squeezing is shown to depend on the photon multiplicity 'm' and the superposition angles of the atoms, θ1 and θ2. One of the quadratures of the atomic polarization is found to exhibit permanent squeezing only for some nonzero values of θ1, as well as θ2. The effect of θ2 on the dipole squeezing, however, is found to be negligible for the initial field in a coherent or a squeezed state. A comparison with the dipole squeezing of a single atom is also presented.