Gatemon qubit on a germanium quantum-well heterostructure

TL;DR

This paper demonstrates a Ge/SiGe heterostructure-based gatemon qubit with gate-tunable frequency, showing promising coherence times and validating a new platform for superconducting qubits using semiconductor weak links.

Contribution

It introduces a novel Ge/SiGe heterostructure platform for gatemon qubits with gate-tunable properties and measurable coherence times, confirming recent findings and advancing qubit development.

Findings

Qubit frequency tunable over 3.5 GHz

Relaxation times up to 119 ns

Ramsey coherence times up to 70 ns

Abstract

Gatemons are superconducting qubits resembling transmons, with a gate-tunable semiconducting weak link as the Josephson element. Here, we report a gatemon device featuring an aluminum microwave circuit on a Ge/SiGe heterostructure embedding a Ge quantum well. Owing to the superconducting proximity effect, the high-mobility two-dimensional hole gas confined in this well provides a gate-tunable superconducting weak link between two Al contacts. We perform Rabi oscillation and Ramsey interference measurements, demonstrate the gate-voltage dependence of the qubit frequency, and measure the qubit anharmonicity. We find relaxation times T$_{1}$ up to 119 ns, and Ramsey coherence times T$^{*}_{2}$ up to 70 ns, and a qubit frequency gate-tunable over 3.5 GHz. The reported proof-of-concept reproduces the results of a very recent work [Sagi et al., Nat. Commun. 15, 6400 (2024)] using similar Ge/SiGe heterostructures thereby validating a novel platform for the development of gatemons and parity-protected cos(2$\phi$) qubits.