  The spin noise of cesium atoms vapor with admixture of buffer gas is
experimentally investigated by measuring the spin induced Faraday rotation
fluctuations in the vicinity of D 2 line. The line, under these conditions, is
known to be strongly inhomogeneously broadened due to the Doppler effect.
Despite that, optical spectrum of the spin noise power, as we have found, has
the characteristic shape of the homogeneously broadened line with the dip at
the line center. This fact is in stark contrast with the results of previous
studies of inhomogeneous quantum dot ensembles. In addition, the two-color
experiments, where correlations of the Faraday rotation fluctuations for two
probe wavelengths were measured, have shown, in a highly spectacular way, that
these fluctuations are either correlated, or anticorrelated depending on
whether the two wavelengths lie on the same side, or on different sides of the
resonance. The experimental data are explained within the developed theoretical
model which takes into account both kinetics and spin dynamics of Cs atoms. It
is shown that the unexpected behavior of the optical Faraday rotation noise
spectra and effective homogenization of the optical transition in the
spin-noise measurements are related to smallness of the momentum relaxation
time of the atoms as compared with their spin relaxation time.

Atomic Physics