Millisecond Coherence in a Superconducting Qubit

Improving control over physical qubits is a crucial component of quantum computing research. Here we report a superconducting fluxonium qubit with uncorrected coherence time T₂^*=1. 48±0. 13 ms, exceeding the state of the art for transmons by an order of magnitude. The average gate fidelity was benchmarked at 0. 99991 (1). Notably, even in the millisecond range, the coherence time is limited by material absorption and could be further improved with a more rigorous fabrication. Our demonstration may be useful for suppressing errors in the next generation quantum processors.