Novel Spectroscopy with Two-Level Atoms in Squeezed Fields
Squeezed light is an example of a nonclassical light field — that is, a field for which quantum mechanics is essential for its description. Since the quantum-mechanical nature of squeezed light is its distinguishing feature, it is clearly of interest to i
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Squeezed light is an example of a nonclassical light field - that is, a field for which quantum mechanics is essential for its description. Since the quantummechanical nature of squeezed light is its distinguishing feature, it is clearly of interest to identify situations in which this field behaves in a radically different way from its nearest classical equivalent. The obvious area to examine is the interaction with atomic systems, and in this chapter, we describe situations in which the use of squeezed light leads to novel effects in atomic spectroscopy. It is demonstrated that the interaction of the squeezed vacuum with even the simplest atomic system, the two-level atom, produces an astonishingly rich range of phenomena. Squeezed light may interact with atomic systems in totally different ways to ordinary light. By isolating the unique characteristics of the squeezed vacuum in its interaction with atomic systems, we open the way to finding new applications. In this chapter, we concentrate on effects which occur in single two-level atoms or systems of two-level atoms, as threelevel atoms are treated in a separate chapter of this book. The emphasis is on identifying phenomena which occur in a squeezed vacuum, but which do not occur for fields with a classical analogue. We shall not describe methods for generating squeezed light. We begin with a brief survey of early investigations. The dynamical response of a two-level atom interacting with a single mode squeezed state was first considered by Milburn [1], who showed that, depending upon the direction of the squeezing, an increase or decrease of the collapse time occurred. The topic received a great stimulus when Gardiner [2] in 1986 showed that the two dipole quadratures of a two-level atom in a squeezed vacuum field may decay at markedly different rates. This modification of the basic radiative processes has significant consequences in spectroscopy, which are reviewed here. Savage and Walls [3] then considered absorptive optical bistability with a squeezed vacuum input and showed that tunneling times may be increased, and the intrinsic stability of the device substantially improved. Milburn [4] pointed out that atomic level shifts would be modified by the presence of the squeezed vacuum. Carmichael, Lane and Walls [5,6] examined the influence of squeezed light on resonance fluorescence, demonstrating P. D. Drummond et al. (eds.), Quantum Squeezing © Springer-Verlag Berlin Heidelberg 2004
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that, under strong laser excitation, the heights and widths of the three spectral lines could be significantly increased or decreased depending upon the phase of the excitation. Janszky and Yushin [7] considered its influence on multi-photon processes. Subsequently, a large number of papers dealt with various aspects of the resonance fluorescence of a single two-level atom (including optical double resonance) [8-28], and with the related problem of the probe absorption spectrum [29-38]. Optical bistability [39,40] and the Jaynes-Cummings model [41-46] were inves
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