Gate-controlled quantum dots and superconductivity in planar germanium

TL;DR

This paper demonstrates the integration of gate-defined quantum dots with superconductivity in planar germanium, overcoming common material issues and showing promising properties for quantum computing hardware.

Contribution

It introduces a novel germanium heterostructure platform with high-mobility holes, gate-tunable superconductivity, and compatibility with standard manufacturing processes.

Findings

High-mobility heavy holes (>500,000 cm²/Vs) confined in germanium quantum wells.

Gate-tunable superconductivity with $I_cR_n$ exceeding 10 μV.

Potential for fast, coherent quantum hardware using germanium.

Abstract

Superconductors and semiconductors are crucial platforms in the field of quantum computing. They can be combined to hybrids, bringing together physical properties that enable the discovery of new emergent phenomena and provide novel strategies for quantum control. The involved semiconductor materials, however, suffer from disorder, hyperfine interactions or lack of planar technology. Here we realise an approach that overcomes these issues altogether and integrate gate-defined quantum dots and superconductivity into a material system with strong spin-orbit coupling. In our germanium heterostructures, heavy holes with mobilities exceeding 500,000 cm$^2$/Vs are confined in shallow quantum wells that are directly contacted by annealed aluminium leads. We demonstrate gate-tunable superconductivity and find a characteristic voltage $I_cR_n$ that exceeds 10 $\mu$V. Germanium therefore has great promise for fast and coherent quantum hardware and, being compatible with standard manufacturing, could become a leading material in the quantum revolution.