  We derive an exact solution of an explicitly time-dependent multichannel
model of quantum mechanical nonadiabatic transitions. In the limit N >>1, where
N is the number of states, we find that the survival probability of the
initially populated state remains finite despite an almost arbitrary choice of
a large number of parameters. This observation proves that quantum mechanical
nonadiabatic transitions among a large number of states can effectively keep
memory about the initial state of the system. This property can lead to a
strongly non-ergodic behavior even in the thermodynamic limit of some systems
with a broad distribution of coupling constants and the lack of energy
conservation.
