Gatemon Qubit on a Germanium Quantum-Well Heterostructure

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 T₁ up to 119 ns, and Ramsey coherence times T₂^* 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. 2024, 15, 6400] using similar Ge/SiGe heterostructures, thereby validating a novel platform for the development of gatemons and parity-protected cos(2ϕ) qubits.

Keywords: 2D materials; Josephson junction; germanium; superconducting qubit.