  We examine energy and particle exchange between finite-sized quantum systems
and find a new form of nonequilibrium states. The exchange rate undergoes
stepwise evolution in time, and its magnitude and sign dramatically change
according to system size differences. The origin lies in interference effects
contributed by multiply scattered waves at system boundaries. Although such
characteristics are utterly different from those of true steady state for
infinite systems, Onsager's reciprocal relation remains universally valid.
