  We propose a nonadiabatic approach to quantum annealing, in which we repeat
quantum annealing in nonadiabatic time scales, and collect the final states of
many realizations to find the ground state among them. In this way, we replace
the diffculty of long annealing time in adiabatic quantum annealing by another
problem of the number of nonsidabatic (short-time) trials. The one-dimensional
transverse-field Ising model is used to test this idea, and it is shown that
nonadiabatic quantum annealing has the same computational complexity to find
the ground state as the conventional adiabatic annealing does. This result
implies that the nonadiabatic method may be used to replace adiabatic annealing
to avoid the effects of external disturbances, to which the adiabatic method is
more prone than the nonadiabatic counterpart.
