Dephasing in quantum chaotic transport: A semiclassical approach

We investigate the effect of dephasing (decoherence) on quantum transport through open chaotic ballistic conductors in the semiclassical limit of small Fermi wavelength to system size ratio, lambda(F)/L < 1. We use the trajectory-based semiclassical theory to study a two-terminal chaotic dot with decoherence originating from (i) an external closed quantum chaotic environment, (ii) a classical source of noise, and (iii) a voltage probe, i.e., an additional current-conserving terminal. We focus on the pure dephasing regime, where the coupling to the external source of dephasing is so weak that it does not induce energy relaxation. In addition to the universal algebraic suppression of weak localization, we find an exponential suppression of weak localization proportional to exp[-(tau) over tilde/tau(phi)], with the dephasing rate tau(-1)(phi). The parameter (tau) over tilde depends strongly on the source of dephasing. For a voltage probe, (tau) over tilde is of order the Ehrenfest time proportional to ln[L/lambda(F)]. In contrast, for a chaotic environment or a classical source of noise, it has the correlation length xi of the coupling or noise potential replacing the Fermi wavelength lambda(F). We explicitly show that the Fano factor for shot noise is unaffected by decoherence. We connect these results to earlier works on dephasing due to electron-electron interactions and numerically confirm our findings.