Coherent Particle Transfer in an On-Demand Single-Electron Source

Electron transfer from a localized state in a quantum dot into a ballistic conductor generally results in particle-hole excitations. We study this effect, considering a resonance level with time-dependent energy coupled to particle states in the Fermi sea. We find that, as the resonance level is driven through the Fermi-level, particle-hole excitations can be suppressed for certain driving protocols. In particular, such noiseless transfer occurs if the level moves with constant rapidity, its energy changing linearly with time. A scheme to study the coherence of particle transfer is proposed.

Figure 1

(a) Quantum dot tunnel coupled to a ballistic conductor. Electrons are periodically trapped on the dot and injected in the conductor as the electron energy $E(t)$ in the dot is increased above the Fermi level when a time-dependent voltage $V(t)$ is applied to the gate. Particle-hole excitations accompanying the injected electron can be detected by the current partition noise on a beam splitter. (b) Schematic diagram of a localized level coupled to a continuum, Eq. (1).

Figure 2

Single-electron current pulse produced by linear driving of a localized state of width $\gamma$ across the Fermi level, $E(t)=ct$. The pulse profile $|\psi (t,x){|}^2$, Eq. (12), for $x>0$, is shown for different values of rapidity $c$. Different curves are offset by $0.5e\gamma$. The asymptotic form is Lorentzian at slow driving, and exponential at fast driving. Note interference fringes at the trailing side of the pulse at $c\gtrsim {\gamma }^2$.

Figure 3

(a) Multiple crossing of the Fermi level in the presence of noise, Eq. (13), leads to creation of particle or hole excitations; (b) Overlap of time intervals and definition of $L(t,t^{\prime },s,s^{\prime })$.