Quantum Oscillator in a Blackbody Radiation Field II. Direct Calculation of the Energy Using the Fluctuation-Dissipation Theorem

An earlier exact result (Phys. Rev. Lerf. 55 (1985). 2273) for the free energy of an oscillatordipole interacting with the radiation field is obtained using the fluctuation-dissipation theorem. A key feature of the earlier calculation, a remarkable formula for the free energy of the oscillator, is obtained in the form of a corresponding formula for the oscillator energy. This confirms, by a longer, more conventional proof, the earlier result. An advantage of this present method is that separate contributions to the energy can be isolated and discussed. Explicit, closed-form expressions are given and the high-temperature limit is discussed. .I-: 1988 Academic Press, Inc.