Hard superconducting gap in a high-mobility semiconductor

Abstract

The co-integration of spin, superconducting and topological systems is emerging as an exciting pathway for scalable and high-fidelity quantum information technology. High-mobility planar germanium is a front-runner semiconductor for building quantum processors with spin-qubits, but the lack of a pristine interface with a superconductor has slowed progress with hybrid superconductorsemiconductor devices. Here we take this step and demonstrate a low-disorder, oxide-free interface between high-mobility planar germanium and a germanosilicide parent superconductor. This superconducting contact is formed by the thermally-activated solid phase reaction between a metal (Pt) and the semiconductor heterostructure (Ge/SiGe). Electrical characterization reveals near-unity transparency in Josephson junctions, hard induced superconducting gap in quantum point contacts, phase control of a Josephson junction in a superconducting quantum interference device, and a superconducting to insulating transition in gated two-dimensional superconductor-semiconductor arrays. These results expand the quantum technology toolbox in germanium and provide new avenues for exploring monolithic superconductor-semiconductor quantum circuits towards scalable quantum information processing.