Current-phase relations of few-mode InAs nanowire Josephson junctions

TL;DR

This study measures the current-phase relation in InAs nanowire Josephson junctions, revealing how the supercurrent's shape and amplitude depend on gate voltage and mode transmission, with implications for quantum computing.

Contribution

It provides the first detailed measurements of gate-tunable, few-mode CPRs in InAs nanowire Josephson junctions, highlighting their potential for quantum applications.

Findings

CPR varies significantly between junctions.

Near supercurrent onset, CPR indicates resonant tunneling through a single mode.

Gate voltage modulates the CPR, consistent with modeled subband structure.

Abstract

Gate-tunable semiconductor nanowires with superconducting leads have great potential for quantum computation and as model systems for mesoscopic Josephson junctions. The supercurrent, $I$, versus the phase, $\phi$, across the junction is called the current-phase relation (CPR). It can reveal not only the amplitude of the critical current, but also the number of modes and their transmission. We measured the CPR of many individual InAs nanowire Josephson junctions, one junction at a time. Both the amplitude and shape of the CPR varied between junctions, with small critical currents and skewed CPRs indicating few-mode junctions with high transmissions. In a gate-tunable junction, we found that the CPR varied with gate voltage: Near the onset of supercurrent, we observed behavior consistent with resonant tunneling through a single, highly transmitting mode. The gate dependence is consistent with modeled subband structure that includes an effective tunneling barrier due to an abrupt change in the Fermi level at the boundary of the gate-tuned region. These measurements of skewed, tunable, few-mode CPRs are promising both for applications that require anharmonic junctions and for Majorana readout proposals.