IN-LOOP SQUEEZING IS LIKE REAL SQUEEZING TO AN IN-LOOP ATOM

Electro-optical feedback can produce an in-loop photocurrent with arbi trarily low noise. This is not regarded as evidence of ''real'' squeez ing because squeezed light cannot be extracted from the loop using a l inear beam splitter. Here I show that illuminating an atom (which is a nonlinear optical element) with ''in-loop'' squeezed light causes lin e narrowing of one quadrature of the atom's fluorescence. This has lon g been regarded as an effect that can only be produced by squeezing. E xperiments on atoms using in-loop squeezing should be much easier than those with conventional sources of squeezed light. [S0031-9007(98)075 12-7].