We investigate dephasing in open quantum chaotic systems in the limit of
large system size to Fermi wavelength ratio, L/λF>>1. We
semiclassically calculate the weak localization correction gwl to the
conductance for a quantum dot coupled to (i) an external closed dot and (ii) a
dephasing voltage probe. In addition to the universal algebraic suppression
gwl∝(1+τD/τϕ)−1 with the dwell time τD through
the cavity and the dephasing rate τϕ−1, we find an exponential
suppression of weak localization by a factor ∝exp[−τ~/τϕ], with a system-dependent τ~. In the
dephasing probe model, τ~ coincides with the Ehrenfest time,
τ~∝ln[L/λF], for both perfectly and partially
transparent dot-lead couplings. In contrast, when dephasing occurs due to the
coupling to an external dot, τ~∝ln[L/ξ] depends on the
correlation length ξ of the coupling potential instead of λF.Comment: 4 pages 3 figures (v2 contains numerous cosmetic changes