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The European Physical Journal B

Time evolution of statistical properties of a radiation field described by a density operator that interpolates between pure and mixing states

C. J. S. Ferreira, TATIANA MARIA RIBEIRO SILVA, B. Baseia

Published Nov 1, 2019• 2 citations
Publisher
DOI
10.1140/epjb/e2019-100335-3

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Any initial state of the radiation field in a finite-Q cavity relaxes towards thermal equilibrium. For the case of a zero-temperature cavity, it is shown that the factorial moments of any photon distribution evolve independently, and have the same time evolution. This is applied to evaluate the transient behaviour of the photon statistics for a variety of initial states of practical interest. The coherences of the density operator obey the same equation of motion as the populations (the photon probability distribution), after a simple transformation. This is used to recover the result that a coherent state remains a pure and coherent state at all times. Also the time-dependent frequency spectrum has been evaluated, and it appeared that this spectrum is the same for any state of the radiation field. The spectral distribution is determined entirely by the cavity damping rate, the spectral width of the detector, and the observation time.