We study the energy level shift of a static two-level atom interacting with a massless scalar field in a thermal bath with the presence of a plane boundary, which gives rise to the Casimir-Polder force. We separately calculate contributions of both thermal fluctuations and radiation reaction using the formalism suggested by J. Dalibard, J. Dupont-Roc, and C. Cohen-Tannoudji [J. Phys. (France) 43, 1617 (1982); 45, 673 (1984)] and analyze in detail the behaviors of the total energy level shifts in three distinct distance regimes in both the low- and high-temperature limits. A comparison of our results with those of a uniformly accelerated atom reveals that uniformly accelerated atoms, in general, do not behave the same as static ones in a thermal bath at the Unruh temperature in terms of the atomic energy level shifts.

• Received 20 September 2009

DOI:https://doi.org/10.1103/PhysRevA.81.012108