Observation of 2e-periodic Supercurrents in Nanowire Single-Cooper-Pair Transistors

TL;DR

This study investigates parity effects in hybrid InAs-Al superconducting transistors, revealing 2e-periodic supercurrents and the influence of magnetic fields on subgap states, which are crucial for topological qubit operation.

Contribution

It provides the first detailed analysis of parity effects and supercurrent modulation in InAs-Al SCPTs, highlighting their relevance for topological quantum computing.

Findings

Observation of 2e-periodic supercurrents at zero magnetic field.

Development of an even-odd pattern with magnetic field.

Parity lifetime decreases exponentially with magnetic field.

Abstract

Parity control of superconducting islands hosting Majorana zero modes (MZMs) is required to operate topological qubits made from proximitized semiconductor nanowires. We, therefore, study parity effects in hybrid InAs-Al single-Cooper-pair transistors (SCPTs) as a first step. In particular, we investigate the gate-charge supercurrent modulation and observe a consistent 2$e$-periodic pattern indicating a general lack of low-energy subgap states in these nanowires at zero magnetic field. In a parallel magnetic field, an even-odd pattern develops with a gate-charge spacing that oscillates as a function of field demonstrating that the modulation pattern is sensitive to the presence of a single subgap state. In addition, we find that the parity lifetime of the SCPT decreases exponentially with magnetic field as the subgap state approaches zero energy. Our work highlights the important role that intentional quasiparticle traps and superconducting gap engineering would play in topological qubits that require quenching of the island charge dispersion.