On-Demand and Tunable Andreev-Conversion of Single-Electron Charge Pulses

Abstract

Electron quantum optics explores coherent single-electron charge pulse propagation in electronic nanoscale circuits akin to table-top photon setups. While past experiments focused on normal-state conductors, incorporating superconductors holds promise for exploiting the electron-hole degree of freedom in quantum sensing applications and quantum information processing. Here, we propose and analyze an on-demand and tunable mechanism for converting single-electron pulses into holes through Andreev processes on a superconductor. We develop a Floquet-Nambu scattering formalism to demonstrate the dynamic conversion of charge pulses and the controllable generation of coherent electron-hole superpositions through interferometric magnetic flux control based on the chiral edge states of a quantum Hall sample. Our discussion covers optimal conditions in realistic scenarios, affirming the feasibility of our proposal with current technology.

Figures (3)

• Figure 1: Andreev conversion of a charge pulse. Clean single-electron states are injected into a chiral edge state by applying Lorentzian-shaped voltage pulses to the input contact. Through partial Andreev reflections on a superconductor, the charge-pulses are converted into coherent superpositions of an electron (e) and a hole (h). The currents before and after the superconductor are shown in blue and red, respectively.
• Figure 2: Andreev conversion of a charge pulse on a superconductor. (a) The time-dependent current, $I(t)$, in the outgoing edge state for different degrees of electron-hole conversion, $\alpha=0$ (full conversion), 0.15, 0.25, 0.3, 0.35, 0.42, 0.45, 0.5, 0.6, 0.7, 0.8, 1 (normal reflection) with the excitation energy well inside the superconducting gap, $\hbar/\tau_0=0.1\Delta$, and $T=0$. (b) The time-dependent current for different excitation energies $\hbar/(\tau_0 \Delta)=0.1$, 0.2, 0.5, 0.66, 1, 2, 10 with perfect electron-hole conversion at the superconductor, $\alpha=0$. The current is divided by the maximum of the injected current denoted by $I_0$.
• Figure 3: Tunable electron-hole conversion. The degree of conversion can be controlled by the phase $\Phi$. The average charge per pulse is shown as a function of $\Phi$ for a symmetric setup with $\alpha_L=\alpha_R$ at different drive frequencies (dashed lines), and for a drive $\hbar/(\tau_0\Delta)=0.1$ for different asymmetric configurations (solid lines). Here, we have taken $\alpha_L=0.41$.