Squashed states of light: theory and applications to quantum spectroscopy

Using a feedback loop it is possible to reduce the fluctuations in one quad rature of an in-loop field without increasing the fluctuations in the other . This effect has been known for a long time, and has recently been called 'squashing' (Buchler et al 1999 Opt. Lett. 24 259), as opposed to the 'sque ezing' of a free field in which the conjugate fluctuations are increased. I n this paper I present a general theory of squashing, including simultaneou s squashing of both quadratures and simultaneous squeezing and squashing. I show that a two-level atom coupled to the in-loop light feels the effect o f the fluctuations as calculated by the theory. In the ideal limit of light squeezed in one quadrature and squashed in the other, the atomic decay can be completely suppressed.