Ehrenfest time and the coherent backscattering off ballistic cavities.

If the Ehrenfest time tau(E) of a ballistic cavity is not negligible in comparison to its dwell time tau(D), the weak localization correction to the cavity's transmission is suppressed proportional to exp(-tau(E/tau(D). At the same time, quantum interference enhances the probability of reflection into the mode of incidence by a factor two. This "enhanced backscattering" does not depend on the Ehrenfest time. We show that, in addition to the diagonal enhanced backscattering, there are off-diagonal contributions to coherent backscattering that become relevant if tau(E) > or = tau(D).