Abstract
We use a modulated oscillator to study quantum fluctuations far from thermal equilibrium. A simple but important nonequilibrium effect that we discuss first is quantum heating, where quantum fluctuations lead to a finite-width distribution of a resonantly modulated oscillator over its quasienergy (Floquet) states. We also discuss the recent observation of quantum heating. We analyze large rare fluctuations responsible for the tail of the quasienergy distribution and switching between metastable states of forced vibrations. We find the most probable paths followed by the quasienergy in rare events, and in particular in switching. Along with the switching rates, such paths are observable characteristics of quantum fluctuations. As we show, they can change discontinuously once the detailed balance condition is broken. A different kind of quantum heating occurs where oscillators are modulated nonresonantly. Nonresonant modulation can also cause oscillator cooling. We discuss different microscopic mechanisms of these effects.
