Supercurrent parity-meter in a nanowire Cooper-pair transistor

TL;DR

This paper demonstrates a supercurrent-based parity-meter in a nanowire Cooper-pair transistor, enabling detection of charge parity states via supercurrent phase shifts, with implications for quantum information manipulation.

Contribution

It introduces a supercurrent parity-meter that detects charge parity states in a nanowire Cooper-pair transistor using phase offsets, advancing quantum measurement techniques.

Findings

Supercurrent phase offset discriminates even and odd charge states.

Parity measurement remains effective near zero-energy subgap states.

Potential for quantum information manipulation using supercurrent interferometry.

Abstract

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.