ENHANCEMENT OF ACTIVATED DECAY OF METASTABLE STATES BY RESONANT PUMPING

We consider the effect of a high-frequency pumping E cos-omega-t on the escape rate of a classical under-damped Brownian particle out of a deep potential well. The pumping frequency-omega is assumed to be close to the frequency-omega(0) of small oscillations. The energy dependence of the oscillation frequency-omega(E) is also assumed to be weak on the scale of thermal energy, omega'E(0)T approximately omega(0)T/U0 << omega(0) [omega'E(0) is the derivative of omega(E) at E = 0, U0 is the barrier height, U0 >> T]. The quadratic (in E) contribution to the decay rate is calculated exactly as a function of two reduced parameters, the anharmonicity of the potential nu = omega'E(0)T/gamma and the resonance detuning delta = [omega-omega(0)]/gamma, where gamma is the friction coefficient. It is shown that the effect of the pumping increases with diminishing \nu\ and at small-nu is proportional to nu-1. In this regime dependence on delta is stepwise: the pumping contribution is large for nu-delta > 0 and small for nu-delta < 0. In the framework of our theory, the decay rate is invariant against the simultaneous change of the signs of delta and nu.