  In this paper, we consider the problem of mean first-passage time (MFPT) in
quantum mechanics; the MFPT is the average time of the transition from a given
initial state, passing through some intermediate states, to a given final state
for the first time. We apply the method developed in statistical mechanics for
calculating the MFPT of random walks to calculate the MFPT of a transition
process. As applications, we (1) calculate the MFPT for multiple-state systems,
(2) discuss transition processes occurring in an environment background, (3)
consider a roundabout transition in a hydrogen atom, and (4) apply the approach
to laser theory.
