Dephasing in the semiclassical limit is system-dependent

Dephasing in open quantum chaotic systems has been investigated in the limit of large system sizes to the Fermi wavelength ratio, L/lambda F >> 1. The weak localization correction g(wl) to the conductance for a quantum dot coupled to (i) an external closed dot and (ii) a dephasing voltage probe is calculated in the semiclassical approximation. In addition to the universal algebraic suppression g wl proportional to (1 + tau(D)/tau(phi))(-1) with the dwell time tau(D) through the cavity and the dephasing rate, we find an exponential suppression of weak localization by a factor of proportional to exp[-(tau) over tilde/tau(phi)], where is the system-dependent parameter. In the dephasing probe model, (tau) over tilde coincides with the Ehrenfest time, (tau) over tilde proportional to ln[L/lambda(F)], for both perfectly and partially transparent dot-lead couplings. In contrast, when dephasing occurs due to the coupling to an external dot, (tau) over tilde proportional to ln[L/xi] depends on the correlation length xi of the coupling potential instead of lambda(F).