Singlet-doublet transitions of a quantum dot Josephson junction detected in a transmon circuit

TL;DR

This paper demonstrates a hybrid superconductor-semiconductor transmon device using an InAs/Al nanowire, enabling the study of quantum dot parity and quasiparticle dynamics, with implications for quantum computing qubits.

Contribution

It introduces a novel gate-controlled quantum dot Josephson junction in a transmon circuit and probes its parity and quasiparticle dynamics via microwave spectroscopy.

Findings

Parity phase diagram matches theoretical predictions

Resolved quasiparticle dynamics across phase boundaries

Potential for realizing semiconductor-based qubits

Abstract

We realize a hybrid superconductor-semiconductor transmon device in which the Josephson effect is controlled by a gate-defined quantum dot in an InAs/Al nanowire. Microwave spectroscopy of the transmon's transition spectrum allows us to probe the ground state parity of the quantum dot as a function of gate voltages, external magnetic flux, and magnetic field applied parallel to the nanowire. The measured parity phase diagram is in agreement with that predicted by a single-impurity Anderson model with superconducting leads. Through continuous time monitoring of the circuit we furthermore resolve the quasiparticle dynamics of the quantum dot Josephson junction across the phase boundaries. Our results can facilitate the realization of semiconductor-based $0-\pi$ qubits and Andreev qubits.