Magnetic-field resilience of 3D transmons with thin-film Al/AlO$_x$/Al Josephson junctions approaching 1 T

TL;DR

This study demonstrates that thin-film aluminum transmons maintain microsecond coherence times and functional operation up to 0.65 T magnetic fields, making them promising for high-field superconducting quantum circuits.

Contribution

We experimentally show that thin-film Al/AlO$_x$/Al Josephson junction transmons exhibit high magnetic-field resilience up to 1 T, with sustained coherence times and operability.

Findings

Transmon frequencies decrease with magnetic field due to superconducting gap suppression.

Microsecond coherence times are maintained up to at least 0.65 T.

SQUID spectroscopy remains feasible up to 1 T.

Abstract

Magnetic-field-resilient superconducting circuits enable sensing applications and hybrid quantum-computing architectures involving spin or topological qubits and electro-mechanical elements, as well as studying flux noise and quasiparticle loss. We investigate the effect of in-plane magnetic fields up to 1 T on the spectrum and coherence times of thin-film 3D aluminum transmons. Using a copper cavity, unaffected by strong magnetic fields, we can solely probe the magnetic-field effect on the transmons. We present data on a single-junction and a SQUID transmon, that were cooled down in the same cavity. As expected, transmon frequencies decrease with increasing fields, due to a suppression of the superconducting gap and a geometric Fraunhofer-like contribution. Nevertheless, the thin-film transmons show strong magnetic-field resilience: both transmons display microsecond coherence up to at least 0.65 T, and $T_1$ remains above 1 $\mathrm{\mu}$s over the entire measurable range. SQUID spectroscopy is feasible up to 1 T, the limit of our magnet. We conclude that thin-film aluminum Josephson junctions are a suitable hardware for superconducting circuits in the high-magnetic-field regime.