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arXiv:2312.13145 · Physical Review Letters

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

Pablo Burset, Benjamin Roussel, Michael Moskalets, Christian Flindt

Published Nov 10, 2025• 3 citations
arXivHTMLPDF

Abstract

Electron quantum optics explores coherent single-electron charge pulse propagation in electronic nanoscale circuits akin to tabletop 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.

DOI
10.1103/lfsm-z1sl

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Electron quantum optics explores coherent single-electron charge pulse propagation in electronic nanoscale circuits akin to tabletop 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.
We propose a source of purely electronic energy-entangled states implemented in a solid-state system with potential applications in quantum information protocols based on electrons. The proposed device relies on the standard tools of electron quantum optics and exploits entanglement of the Cooper pairs of a BCS superconductor. The latter is coupled via an adjustable quantum point contact to two opposite spin-polarized electron wave-guides, which are driven by trains of Lorentzian pulses. This specific choice for the drive is crucial to inject purely electronic entangled states devoid of spurious electron–hole pairs. In the Andreev regime, a perturbative calculation in the tunnel coupling confirms that entangled electrons states are generated at the output of the normal side. For arbitrary tunnel coupling and for a periodic drive, direct current and noise (auto and cross correlations) are computed numerically using a Keldysh–Nambu–Floquet formalism. Importantly, for a periodic drive, the production of these states can be controlled in time, thus implementing an on-demand source of entangled states. We exploit realistic experimental parameters for our device to identify its optimal functioning point.
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Coherent control of quantum states has been demonstrated in a variety of superconducting devices. In all of these devices, the variables that are manipulated are collective electromagnetic degrees of freedom: charge, superconducting phase, or flux. Here we demonstrate the coherent manipulation of a quantum system based on Andreev bound states, which are microscopic quasi-particle states inherent to superconducting weak links. Using a circuit quantum electrodynamics setup, we performed single-shot readout of this Andreev qubit. We determined its excited-state lifetime and coherence time to be in the microsecond range. Quantum jumps and parity switchings were observed in continuous measurements. In addition to having possible quantum information applications, such Andreev qubits are a test-bed for the physics of single elementary excitations in superconductors.
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We propose a source of purely electronic energy-entangled states implemented in a solid-state system with potential applications in quantum information protocols based on electron flying qubits. The proposed device relies on the standard tools of electron quantum optics and exploits entanglement of the Cooper pairs of a BCS superconductor. The latter is coupled via an adjustable quantum point contact to two opposite spin-polarized electron waveguides, which are driven by trains of Lorentzian pulses. This specific choice for the drive is crucial to inject purely electronic entangled states devoid of spurious electron-hole pairs. In the Andreev regime, a perturbative calculation in the tunnel coupling confirms that entangled electron states are generated at the output of the normal side. We introduce a quantity related to charge current cross correlations which allows one to experimentally verify the entangled nature of the emitted state.