We study a Cooper-pair transistor realized by two Josephson weak links that enclose a superconducting island in an InSb-Al hybrid nanowire. When the nanowire is subject to a magnetic field, isolated subgap levels arise in the superconducting island and, due to the Coulomb blockade,mediate a supercurrent by coherent co-tunneling of Cooper pairs. We show that the supercurrent resulting from such co-tunneling events exhibits, for low to moderate magnetic fields, a phase offset that discriminates even and odd charge ground states on the superconducting island. Notably,this phase offset persists when a subgap state approaches zero energy and, based on theoretical considerations, permits parity measurements of subgap states by supercurrent interferometry. Such supercurrent parity measurements could, in a new series of experiments, provide an alternative approach for manipulating and protecting quantum information stored in the isolated subgap levels of superconducting islands.
@article{arxiv.2107.08466,
title = {Supercurrent parity-meter in a nanowire Cooper-pair transistor},
author = {Ji-Yin Wang and Constantin Schrade and Vukan Levajac and David van Driel and Kongyi Li and Sasa Gazibegovic and Ghada Badawy and Roy L. M. Op het Veld and Joon Sue Lee and Mihir Pendharkar and Connor P. Dempsey and Chris J. Palmstrøm and Erik P. A. M. Bakkers and Liang Fu and Leo P. Kouwenhoven and Jie Shen},
journal= {arXiv preprint arXiv:2107.08466},
year = {2022}
}