Two-Level Atom at Finite Temperature
T. Sowiński
Center for Theoretical Physics, Polish Academy of Sciences, al. Lotników 32/46, 02-668 Warsaw, Poland
Faculty of Biology and Environmental Sciences, Cardinal Stefan Wyszynski University, Wóycickiego 1/3, 01-938 Warsaw, Poland
Received: October 26, 2009
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Properties of a two-level atom coupled to the quantized electromagnetic field at finite temperature are determined. The analysis is based on a new method (inspired by quantum electrodynamics) of describing qubits, developed previously at zero temperature. In this paper, we make a generalization to finite temperature by introducing the Matsubara formalism and the temperature propagators. We analyze the spectral properties of different types of propagators and we derive a direct connection between the temperature propagators and the real time propagators. To show the effectiveness of this method, we calculate the temperature dependence of the polarizability of a two-level atom in the lowest order of perturbation theory and we predict an unexpected sharpening of the resonance. The whole discussion is carried out without the rotating wave approximation.
DOI: 10.12693/APhysPolA.116.994
PACS numbers: 11.10.Wx, 32.10.Dk, 31.15.ap, 32.70.Jz