Gate- and flux-tunable sin(2φ) Josephson element with planar-Ge junctions

Abstract

A planar-Ge Josephson interferometer is tuned to an almost π-periodic current-phase relation dominated by charge-4e transport.

Measured a sin(2φ) contribution reaching 95.2% of the total supercurrent.
Suppressed the first harmonic by roughly two orders of magnitude through gate and flux tuning.
Demonstrated a high-purity building block for parity-protected superconducting qubits, not a complete qubit benchmark.