Tunable nonadiabatic excitation in a single-electron quantum dot

We report observation of nonadiabatic excitation of single electrons in a quantum dot. We have developed a way of measuring the excitation spectrum of the quantum dot formed in a tunable-barrier single-electron pump. When the confinement potential is deformed at sub-nanosecond timescales, electrons are excited to states with higher back-tunneling rates leading to a measureable reduction in the pumped current. In the presence of a perpendicular magnetic field we have observed that these states follow a Fock-Darwin spectrum. Our experiments demonstrate a simple model system to study nonadiabatic processes of quantum particles.