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

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 singleimpurity 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 − π qubits and Andreev qubits.

Tunable Planar Josephson Junctions Driven by Time-Dependent Spin-Orbit Coupling

“…However, we expect that our focus only on linearized Rashba SOC, easily tunable by E-field [33,34], already clarifies its important role in JJ dynamics. With changing SOC, there are further opportunities for gate-controlled Majorana states and probing their non-Abelian statistics [77,78] or an added tunability in the implementation of superconducting qubits [3,79,80]. This would extend the previously studied qubit tunability by voltage or flux [3,81] as well as the use of π-phase states for an improved qubit operation [82,83].…”