Quantum dynamics of an electromagnetic mode in a cavity

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Abstract
The problem of an electromagnetic mode in a cavity is analyzed by means of functional integrals. Our approach follows the Feynman-Vernon method in the coherent-state representation. The reduced density operator for the electromagnetic mode is evaluated. Its matrix elements in the occupation-number representation are computed and it is shown that off-diagonal elements of this operator decay in time very rapidly. The farther they are from the main diagonal the faster they decay. This is another example showing how quantum interference is destroyed in a nonisolated system.