Cold atoms: Statistics of dressed modes in a thermal state
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2002 Elsevier Science B.V. All rights reserved. By a Wigner-function calculation, we evaluate the trace of a certain Gaussian operator arising in the theory of a boson system subject to both finite temperature and (weak) interaction. Thereby we rederive (and generalize) a recent result by Kocharovsky, Kocharovsky, and Scully [phys. Rev. A 61(2000) 053606] in a way that is technically much simpler. One step uses a special case of the response ofWigner functions to linear transformations, and we demonstrate the general case by simple means. As an application we extract the counting statistics for each mode of the Bose gas.