  We study the many-body electronic state created by a time-dependent drive of
a mesoscopic contact. The many-body state is expressed manifestly in terms of
single-electron and electron-hole quasiparticle excitations with the amplitudes
and probabilities of creation which depend on the details of the applied
voltage. We experimentally probe the time dependence of the constituent
electronic states by using an analog of the optical Hong-Ou-Mandel correlation
experiment where electrons emitted from the terminals with a relative time
delay collide at the contact. The electron wave packet overlap is directly
related to the current noise power in the contact. We have confirmed the time
dependence of the electronic states predicted theoretically by measurements of
the current noise power in a tunnel junction under harmonic excitation.

Mesoscale and Nanoscale Physics