Phase-dependent Resonance Fluorescence Spectra For Two-level Atoms

H. Z. Zhao, Zhou Lu, John E. Thomas

H. Z. Zhao, Zhou Lu, A. M. Bacon +2 more

We measure phase-dependent fluorescence spectra for an elementary system: long-lived coherently driven two-level atoms in an atomic beam. Phase-dependent fluorescence spectra measure quadrature noise in the atomic radiation field. These noise spectra are obtained using a homodyne detection scheme that suppresses excess noise by subtracting signals from two identically prepared atomic samples. Noise spectra are obtained for atomic radiation which is in phase $(0\ifmmode^\circ\else\textdegree\fi{})$ and out of phase $(90\ifmmode^\circ\else\textdegree\fi{})$ with a resonant driving field, as well as $\ifmmode\pm\else\textpm\fi{}45\ifmmode^\circ\else\textdegree\fi{}$ out of phase with an off-resonant driving field. The measured phase-dependent fluorescence spectra are much richer than ordinary fluorescence spectra, and exhibit many novel features. Particularly interesting are phase-dependent noise spectra for off-resonant excitation. These strikingly exhibit direct manifestations of time ordering, which appear as large differences between the measured $45\ifmmode^\circ\else\textdegree\fi{}$ and $\ensuremath{-}45\ifmmode^\circ\else\textdegree\fi{}$ quadrature noise spectra. The measured noise spectra are in excellent agreement in magnitude and shape with the results of a quantum treatment using no free parameters.

H. Z. Zhao, Zhou Lu, John E. Thomas

We measure phase-dependent fluorescence spectra of two-level atoms driven by a monochromatic laser field, for off-resonance excitation. Pairs of spectra with phases of opposite sign are found to display striking differences that arise entirely from time ordering.

H. Walther

Constantine Mavroyannis

Shao-yan Gao, Fuli Li, Shi-Yao Zhu