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Physical Review A

Dispersive profiles in resonance fluorescence of a two-level atom in a squeezed vacuum

S. Smart, S. Swain

Published Jul 1, 1993• 56 citations
Publisher

Abstract

We report unusual profiles in the resonance fluorescence spectrum of a two-level atom interacting with a resonant classical field of intermediate intensity and a squeezed vacuum. These have a dispersive profile, quite unlike any previously described, and are a distinctive feature of the interaction of atomic systems with nonclassical fields. An approximate analytic expression is obtained which explains these features, and it is shown that they arise from atomic correlations not probed in normal resonance fluorescence.

DOI
10.1103/physreva.48.r50

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We report unusual profiles in the resonance fluorescence spectrum of a two-level atom interacting with a resonant classical field of intermediate intensity and a squeezed vacuum. These have a dispersive profile, quite unlike any previously described, and are a distinctive feature of the interaction of atomic systems with nonclassical fields. An approximate analytic expression is obtained which explains these features, and it is shown that they arise from atomic correlations not probed in normal resonance fluorescence.
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 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.
The authors investigate the dipole-dipole interaction role in the resonance fluorescence of two identical two-level atoms, which are confined to a region much smaller than the resonant wavelength and which are damped by a squeezed vacuum. The spectrum consists of seven or five lines, depending on the relative phase between the driving field and the squeezed vacuum, whereas the spectrum without the dipole-dipole interaction displays three lines. The widths of these lines depend on the parameters of the squeezed vacuum and can be subnatural or supernatural depending on the phase. The central line and additional sidebands at double the Rabi frequency can have intensities larger than in the normal vacuum but the intensities of lines at one Rabi frequency are always less than in the normal vacuum.
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.
The steady-state resonance fluorescence spectrum of a two-level atom driven by a bichromatic field in a broadband squeezed vacuum is studied. When the carrier frequency of the squeezed vacuum is tuned to the frequency of the central spectral line, anomalous spectral features, such as hole burning and dispersive profiles, can occur at the central line. We show that these features appear for wider, and experimentally more convenient, ranges of the parameters than in the case of monochromatic excitation. The absence of a coherent spectral component at the central line makes any experimental attempt to observe these features much easier. We also discuss the general features of the spectrum. When the carrier frequency of the squeezed vacuum is tuned to the first odd or even sidebands, the spectrum is asymmetric and only the sidebands are sensitive to phase. For appropriate choices of the phase the linewidths of only the odd or even sidebands can be reduced. A dressed-state interpretation is provided.
We study the system of a single two-level atom interacting with a braodband squeezed vacuum and a classical applied field. The atom is subject to collisions, and the applied field may possess a finite linewidth. The atomic populations, coherences, resonance fluorescence spectrum, and intensity fluctuation spectrum are calculated. Wherever practicable, analytic expressions are obtained that show the dependence of these quantities on the damping parameters. Numerical plots are presented. Two qualitative results that we obtain are the following: (a) we show that the dependence of the populations on the squeezing phase is increased by increasing the damping parameters, contrary to what might at first have been expected, and (b) we show that, in the absence of external damping, the squeezing induces strong asymmetries in the off-resonant resonance fluorescence spectra.