ANOMALOUS FLUORESCENCE-SPECTRA IN AN EXTREMELY WEAK, BROAD-BAND SQUEEZED VACUUM UNDER MONOCHROMATIC AND BICHROMATIC EXCITATION

We show that a two-level atom interacting with an extremely weak squee zed vacuum can display resonance fluorescence spectra that are qualita tively different to those that can be obtained using fields with a cla ssical analogue. We consider first the free space situation with monoc hromatic excitation, and then discuss a bichromatically driven two-lev el atom in a cavity as a practical scenario for experimentally detecti ng the anomalous features predicted. We show that in the bad cavity li mit, the anomalous spectral features appear for a weak squeezed vacuum and large frequency differences of the bichromatic field, conditions which are easily accessible in laboratories. The advantage of bichroma tic, as opposed to monochromatic, excitation is that there is no coher ent scattering at line centre which could obscure the observations. A scaling law is derived, N similar to Omega(4) which relates the squeez ed photon number to the Rabi frequency at which the anomalous features appear. (C) 1998 Elsevier Science B.V.