Giant mesoscopic fluctuations of quantum dot conductance caused by strong electromagnetic irradiation

Resonant backscattering of electrons from a quantum dot adiabatically connected to reservoirs is shown to be possible under certain conditions in the presence of an electromagnetic field. This novel effect occurs for electron energies close to quasienergy levels formed by level mixing induced by the radiation field. As a result the conductance traced as a function of frequency, bias, or gate voltage has a characteristic pattern of ''dips'' to zero conductance. If the radiation intensity is increased, the distribution of dips goes through a reentrance transition from order to disorder and back to order. Analytical results are confirmed by direct numerical calculations.