Electron and electron-hole quasiparticle states in a driven quantum contact

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.

Figure 1

(a)–(d) Wave functions ${\left|\mathbf{v}\left(t\right)\right|}^2$ and $|{\mathbf{u}}_{\pm }{\left(t\right)|}^2$ of electrons and electron-hole pairs created by different voltage drives $V\left(t\right)$. The corresponding nonequilibrium distribution functions are shown in the panels (e)–(h).

Figure 2

Noise $S_2$ as a function of a time delay $\tau$ between two harmonic signals applied at the leads: (a) $N=1$ and $e{V}_0/\omega =1.5$, 1, $0.5$ (solid lines, top to bottom); (b) left lead: $N=1, e{V}_0/\omega =0.5$; right lead: $N=0, e{V}_0/\omega =2$; and (c) left lead: $N=1, e{V}_0/\omega =1$; right lead: $N=0, e{V}_0/\omega =2$. Approximations for $S_2$ calculated using the overlaps $C\left(\tau \right)$ of the wave functions depicted in Fig. 1 are shown for comparison (dash-dotted lines). (d)–(f) $S_2\left(\tau \right)$ measured in a tunnel junction at $\omega /2\pi =20\mathrm{GHz}$ (symbols). Theoretical results are shown for temperatures $T_e=0$ (solid lines) and $T_e=0.1\omega$ (dashed lines).