Nonexponential Decay in the Quantum Dynamics of Nanosystems

The quantum dynamical problem is solved fora system coupled to an equidistant-spectrum bath with the energy difference Omega between the neighboring levels n and n + 1 and the coupling matrix elements C-n(2) = C-2(1 + Delta(-2)n(2))(-1) constraining the energy interval comprising the bath states interacting with the system. The evolution in the strong-coupling limit is determined by two parameters, Gamma = pi C-2/Omega >> 1 and alpha = Gamma/Delta. If alpha not equal 0, then the decrease in the population in the initial cycle with a period of 2 pi/Omega is not exponential and the effective rate constant increases with time. The results qualitatively explain the appearance of nonexponential relaxation regimes for a dense-spectrum nanosystem and predict the possibility of the multiple recovery of the initial-state population.