Quantum-to-classical crossover of mesoscopic conductance fluctuations

We calculate the system-size-over-wavelength (M) dependence of sample-to-sample conductance fluctuations, using the open kicked rotator to model chaotic scattering in a ballistic quantum dot coupled by two N-mode point contacts to electron reservoirs. Both a fully quantum-mechanical and a semiclassical calculation are presented, and found to be in good agreement. The mean-squared conductance fluctuations reach the universal quantum limit of random-matrix theory for small systems. For large systems they increase proportional toM(2) at fixed mean dwell time tau(D)proportional toM/N. The universal quantum fluctuations dominate over the nonuniversal classical fluctuations if N<rootM. When expressed as a ratio of time scales, the quantum-to-classical crossover is governed by the ratio of Ehrenfest time and ergodic time.