Observation of Photon-Assisted Tunneling through a Quantum Dot

We have measured dc transport through a GaAs/AlGaAs quantum dot in the presence of a microwave signal of frequency $f$. We find features related to the photon energy $\mathrm{hf}$ whose positions in gate voltage are independent of the microwave power buy vary linearly with frequency. The measurements demonstrate photon-assisted tunneling in the mesoscopic regime. A comparison is made with a model that extends Coulomb blockade theory to include photon-assisted tunneling.