Squeezing and feedback

Abstract

Electro-optical feedback has many features in common with optical nonlinearities and hence is relevant to the generation of squeezing. First, I discuss theoretical and experimental results for traveling-wave feedback, emphasizing how the ``in-loop'' squeezing (also known as ``squashing'') differs from free squeezing. Although such feedback, based on ordinary (demolition) photodetection cannot create free squeezing, it can be used to manipulate it. Then I treat feedback based on nonlinear quantum optical measurements (of which non-demolition measurements are one example). These {\em are} able to produce free squeezing, as shown in a number of experiments. Following that I discuss theories showing that intracavity squeezing can be increased using ordinary feedback, and produced using QND-based feedback. Finally, I return to ``squashed'' fields and present recent results showing that the reduced in-loop fluctuations can suppress atomic decay in a manner analogous to the effect for squeezed fields.