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Journal of Experimental and Theoretical Physics

Semiclassical approach to resonance-optics polarization effects in coherent and squeezed fields

Ashat M. Basharov

Published Jan 1, 1997• 5 citations
Publisher

Abstract

Equations are derived for the atomic density matrix and relaxation operator for a broadband squeezed field in an arbitrary polarization state and resonance atomic energy levels with an arbitrary degree of degeneracy. It is shown that suppression of the relaxation of the quadrature component of the atomic polarization depends strongly on the type of resonance transition and the polarization state of the squeezed and coherent perturbing fields. When the resonance levels are strongly degenerate, the relaxation of the quadrature component of the atomic polarization under conditions of maximum suppression is nonexponential in character. The mathematical apparatus developed here makes it possible to calculate polarization-related aspects of the multifrequency optical behavior of atomic and molecular systems resonantly excited both by coherent light and by broadband squeezed fields.

DOI
10.1134/1.558142

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Equations are derived for the atomic density matrix and relaxation operator for a broadband squeezed field in an arbitrary polarization state and resonance atomic energy levels with an arbitrary degree of degeneracy. It is shown that suppression of the relaxation of the quadrature component of the atomic polarization depends strongly on the type of resonance transition and the polarization state of the squeezed and coherent perturbing fields. When the resonance levels are strongly degenerate, the relaxation of the quadrature component of the atomic polarization under conditions of maximum suppression is nonexponential in character. The mathematical apparatus developed here makes it possible to calculate polarization-related aspects of the multifrequency optical behavior of atomic and molecular systems resonantly excited both by coherent light and by broadband squeezed fields.
The resonance fluorescence system of a coherently driven two-level atom in the presence of a broadband squeezed vacuum field whose central frequency is not in resonance with either the driving field frequency or the atomic transition frequency is analyzed. Solutions of the Bloch equations of the system are presented in terms of continued fractions for arbitrary strength of the coherent driving field. Numerical results are presented for the first-harmonic quadrature components of the absorption spectrum and the fluorescent intensity. The effects of the squeezed vacuum field detuning on the absorption spectrum result in hole burning or a dip structure in the weak-field case and two absorption–amplification peaks in the strong-field case. Results are sensitive to the relative phase of the squeezed vacuum.
The relaxation process of a single two-level atom driven by an intense resonant coherent field is studied in the presence of a broadband squeezed vacuum field. Generalized forms for the self-field operator and the field-dependent damping coefficients are derived. In the steady state, positive atomic inversion (~5%) is shown for some range of the phase of the squeezed vacuum field. The squeezing-induced enhanced and asymmetric coherence (i.e.?non-zero dispersive atomic polarization) induces profound asymmetry in the side-bands of the Mollow fluorescent spectrum and the absorptive?dispersive spectra near the Rabi side-band frequencies. The case of two and three cooperative atoms, instead of a single atom, shows (i)?positive atomic inversion in the steady state for larger interval of the squeeze phase parameter and more enhanced extrema for the atomic polarization components and (ii) the extra side peaks in the fluorescent spectrum become asymmetric and of dispersive-like profile. Dressed-state analysis in the single-atom case with the field-dependent decay process in the presence of the squeezed vacuum field is presented and shows that the inequality of the (field-dependent) decay rates of the dressed states leads to more positive inversion in the dressed states as compared with the normal vacuum case.
Abstract The physical processes forming the saturated absorption resonance spectra at a number of degenerate atomic transitions at their interaction with coherent optical fields and incoherent ield of spontaneous radiation of excited atoms are studied numerically. The features of behavior of nonlinear resonance spectra depending on the degree of degeneration and relaxation parametersof level transitions, character of polarizations and intensities, as well as direction of propagation of optical fields are analyzed.
The radiation of a quantum particle in a thermostatic electromagnetic field with a nonzero photon density in the presence of a strong Stark interaction between the particle and field is considered. New fundamental effects—the suppression of radiation by the Stark interaction in an intense broadband field and an additional “decay” shift in the energy of the decaying level, which is different from the Lamb and Stark level shifts—have been established. A new effect of the suppression of radiation is complementary to the effect of suppression of the polarization relaxation of the quantum particle in a squeezed field, which is discovered earlier by Gardiner. The new effect can occur independently of the effect established by Gardiner.
The behavior of a two-level atom confined within a cavity, pumped by an intense external field, and damped by a squeezed vacuum reservoir is studied. When the lowest squeezed quadrature of the vacuum is in phase with the pumping field, the relaxation time of the population inversion and of the polarization quadratures of the atom are appreciably enlarged, and hence the atom is decoupled from the reservoir. The effects of finite bandwidth of the squeezing are analyzed and it is shown that they can be used to improve the decoupling.
Atom radiation in a squeezed thermal reservoir is studied. We show that, as in the case of a squeezed vacuum reservoir, the two quadratures of the atomic polarization are damped at different rates. When the atom is driven by a coherent field, we find that the steady-state polarization depends on the relative phase of the squeezing and the driving field. However, this phase dependence becomes less pronounced when the number of thermal photons increases. The fluorescent spectrum is calculated in the strong-driving-field limit by employing the secular approximation. Properties of the spectrum and the possibility of a subnatural linewidth are investigated.