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Physical Review A

Anomalous resonance fluorescence from an atom in a cavity with injected squeezed vacuum

William Smyth, S. Swain

Published Apr 1, 1996• 38 citations
Publisher

Abstract

As a realistic system for observing the distinctive features of the interaction of squeezed light with atoms, we consider a single, coherently driven, two-level atom in a resonant optical cavity coupled to a broadband squeezed vacuum field. In the bad cavity limit we derive equations of motion for the atomic operators that are identical to those for the free-space situation, except for having modified parameters. We focus our attention on the resonance fluorescence from this system and show that, in the above limit, many of the unusual spectral features previously reported for the free atom situation persist. We also confirm the link between these anomalous spectra and the collapse of an atom into a pure state. The cavity parameter values needed to verify some of these interesting effects appear to be within the range of present day technology. \textcopyright{} 1996 The American Physical Society.

DOI
10.1103/physreva.53.2846

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As a realistic system for observing the distinctive features of the interaction of squeezed light with atoms, we consider a single, coherently driven, two-level atom in a resonant optical cavity coupled to a broadband squeezed vacuum field. In the bad cavity limit we derive equations of motion for the atomic operators that are identical to those for the free-space situation, except for having modified parameters. We focus our attention on the resonance fluorescence from this system and show that, in the above limit, many of the unusual spectral features previously reported for the free atom situation persist. We also confirm the link between these anomalous spectra and the collapse of an atom into a pure state. The cavity parameter values needed to verify some of these interesting effects appear to be within the range of present day technology. \textcopyright{} 1996 The American Physical Society.
We consider a two-level atom in an optical cavity driven by a coherent field and coupled to broadband squeezed vacuum. In the bad-cavity limit, the cavity field can be adiabatically eliminated, leaving equations of motion for atomic operators similar to those of free-space resonance fluorescence. We calculate the incoherent spectrum of the fluorescent light field and find that the cavity-enhanced spontaneous emission can be suppressed, and a subnatural linewidth obtained, for the correct choice of the phase of the squeezed input relative to the coherent driving field.
We show that the resonance fluorescence of a two-level atom interacting with a squeezed vacuum can show a wide variety of anomalous features (including hole burning at line center) over a continuous but very narrow range of parameter values. The spectra have a variety of profiles, all of which are qualitatively different from those observed in normal resonance fluorescence and are a distinctive manifestation of the presence of the nonclassical field. The anomalous features persist in a cavity environment, which provides the best means for their experimental observation.
We study the two-photon excitation rate and the spectrum of a three-level atom in the \ensuremath{\Xi} configuration interacting with a resonant cavity mode which is coupled to a broadband squeezed vacuum through its input-output mirror. We show that the optical Bloch equations in the cavity environment are formally identical to these in free space but, in the bad-cavity limit, with cavity-modified parameters describing the injected squeezed vacuum. It is shown that the two-photon excitation rate (which is proportional to the upper-level population) has two components, one depending linearly and the other quadratically on the squeezed photon number N, in excellent agreement with experiment [Georgiades et al., Phys. Rev. Lett. 75, 3426 (1995)]. The presence of the term quadratic in N is entirely due to the effectively imperfect correlation of the squeezed photon pairs in the bad cavity. We also find that the two-photon excitation spectrum (as measured by the fluorescent emission from the upper level to the intermediate level) exhibits an extremely narrow peak at line center, under appropriate choices of the bad-cavity parameters. All these results are independent of the squeezed phase. \textcopyright{} 1996 The American Physical Society.
It has been suggested that phased atomic decay in a squeezed vacuum could be detected in the fluorescence spectrum emitted from a driven two-level atom in a cavity. Recently, the existence of other very distinctive features in the fluorescence spectra arising from the nonclassical features of the squeezed vacuum has been reported. In this paper, we investigate the possibility of experimental observation of these spectra. The main obstacle to the experimentalist is ensuring an effective squeezed-vacuum-atom coupling. To overcome this problem we propose the use of a Fabry-P\'erot microcavity. The analysis involves a consideration of the three-dimensional nature of the electromagnetic field, and the possibility of a mismatch between the squeezed and cavity modes. The problem of squeezing bandwidths is also addressed. We show that under experimentally realistic circumstances many of the spectral anomalies predicted in free space also occur in this environment. In addition, we report large population inversions in the dressed states of the two-level atom.
We discuss the conditions which give rise to anomalous features in the resonance fluorescence of a two-level atom interacting with a resonant classical field and a squeezed vacuum. A simple expression is obtained, which is shown to coincide closely with the conditions for amplification of a probe beam and with the collapse of the atomic system into a pure state. We thereby illustrate striking observable consequences of the evolution of a driven system into a pure state. This situation also provides a method for preparing an atom in a pure state whose nature depends on the squeezing phase and Rabi frequency. The conditions for hole burning are obtained analytically, and the sensitivity of these effects to the two-photon correlations produced by the squeezed vacuum is demonstrated.
A single two-level atom in a coherently driven cavity and damped by a broadband squeezed vacuum centered about the atomic transition frequency is studied. A second-order Fokker-Planck equation for this system is obtained without using system size expansion. Effects of detunings and cavity decays are also incorporated in the Fokker-Planck equation. This equation is used to study atomic inversion, fluorescent spectrum, and the intensity correlations of the transmitted and fluorescent photons in the bad-cavity limit. Several interesting effects in the atomic inversion, spectrum, and intensity correlations due to the squeezed vacuum are presented. These results are also compared with an atom that is damped by a thermal reservoir.