Quench dynamics of fermion-parity switches in a Josephson junction

TL;DR

This paper studies the real-time charge transfer in a Josephson junction during a fermion parity switch, revealing how the transferred charge depends on the driving speed and coupling energies, enabling controlled quasiparticle generation.

Contribution

It introduces a theoretical framework for understanding charge transfer dynamics during fermion parity transitions in Josephson junctions, highlighting the dependence on driving speed and coupling parameters.

Findings

In the adiabatic limit, a single quasiparticle transfers charge e.

In the quenched limit, charge transfer varies between 0 and e depending on coupling energies.

The method enables on-demand generation of charge-neutral quasiparticles.

Abstract

A Josephson junction may be driven through a transition where the superconducting condensate favors an odd over an even number of electrons. At this switch in the ground-state fermion parity, an Andreev bound state crosses through the Fermi level, producing a zero-mode that can be probed by a point contact to a grounded metal. We calculate the time-dependent charge transfer between superconductor and metal for a linear sweep through the transition. One single quasiparticle is exchanged with charge $Q$ depending on the coupling energies $\gamma_1,\gamma_2$ of the metal to the Majorana operators of the zero-mode. For a single-channel point contact, $Q$ equals the electron charge $e$ in the adiabatic limit of slow driving, while in the opposite quenched limit $Q=2e\sqrt{\gamma_1\gamma_2}/(\gamma_1+\gamma_2)$ varies between $0$ and $e$. This provides a method to produce single charge-neutral quasiparticles on demand.