In-Loop Squeezing Is Like Real Squeezing to an In-Loop Atom

Abstract

Electro-optical feedback can produce an in-loop photocurrent with arbitrarily low noise. This is not regarded as evidence of "real" squeezing because squeezed light cannot be extracted from the loop using a linear beam splitter. Here I show that illuminating an atom (which is a nonlinear optical element) with "in-loop" squeezed light causes line narrowing of one quadrature of the atom's fluorescence. This has long been regarded as an effect that can only be produced by squeezing. Experiments on atoms using in-loop squeezing should be much easier than those with conventional sources of squeezed light.[ S0031-9007(98)

Effects of twin-beam “squashed” light on a three-level atom

“…A recent letter [5] by one of us showed that squashed light also produces a similar line-narrowing, and so this "direct effect" is one of non-classical correlations rather than solely of squeezing. The work on squashed light spectroscopy of two-level atoms was recently extended to include simultaneous squeezing and squashing [3].…”

“…There are various ways of achieving this including the one pictured, which is detailed in Ref. [5]. The resultant field, b(t), is incident on a two-level atom.…”

“…See Ref. [5] for details on mode-matching. Assuming the squeezed light is broadband compared to the atomic linewidth, we can make the white noise approximation that the quadrature spectra are constant.…”

“…For fields with zero mean, as are all the fields in this paper, the X quadrature spectrum is defined as 5) and similarly for the Y quadrature spectrum. It can then be shown that for a stationary free field 6) which is known as the Heisenberg inequality [14,15].…”

“…Although based on the same techniques as in [5], the development of the model for the three-level system required a complete redesign of the feedback mechanism. Non-classical excitation of a three-level atom requires non-classical correlations between two fields, i.e.…”