Electron dynamics of a single quantum dot probed with wideband millimeter-wave spectroscopy

We perform microwave spectroscopy on a single quantum dot using a compact pulsed spectrometer. Although DC transport shows strong elastic cotunneling in the Coulomb blockade regime and inelastic tunneling in the single-electron tunneling (SET) regime, these effects are suppressed under picosecond impulses whose energies are commensurate with those of the dot. Instead, under non-zero bias we find excited-state resonances in the induced complex photoconductance as well as strong deviations of the dot capacitance compared to equilibrium values, a signature of the effective relaxation times of SET.