FLUCTUATIONS IN QUANTUM AND CLASSICAL POPULATIONS

Characterization and measurement of fluctuations in quantum and classical populations are compared. A simple method for estimating the population fluctuation time is outlined and approximate quantum and classical expressions for the two-time correlation function are derived. The utility of the method is demonstrated through analysis of the Scully-Lamb laser model, where it is shown to give correlation times in good agreement with numerical calculations for lasers operated below, at, and above threshold. Discrepancies in the predictions of a previous similar method are shown to originate from inconsistent separation of its quantum and classical versions.