Electron and electron–hole excitations in a driven Fermi sea

We study the response of a degenerate Fermi sea to a time-dependent perturbation. We find that elementary excitations in the Fermi sea are electrons and electron–hole quasiparticle pairs whose number and probability of creation depend on amplitude and shape of the drive. The excitations can be probed in a driven quantum contact at low temperature. While electronic excitations are associated to the dc voltage offset and determine the average current, the electron–hole pairs are created by the ac voltage component and give rise to the excess current noise power in a junction. We also obtain the many-body state created by the drive. The constituent quasiparticle states can be probed by a Hong–Ou–Mandel type of correlation experiment where electrons emitted from the terminals with a relative time delay collide at the contact. The current noise power in the junction is directly related to the wave packet overlap at the contact. This is confirmed in recent experiments, demonstrating an unprecedented degree of control of elementary excitations in a coherent mesoscopic junction.