A superconducting cavity qubit with tens of milliseconds single-photon coherence time*

Long-lived memory qubits can significantly reduce error correction overheads in future quantum processors. Superconducting cavities, capable of reaching quality factors well beyond one billion, are promising candidates for such quantum memories. However, these high-Q cavities are yet to be leveraged to achieve extended coherence times due to their coupling to noisy ancilla qubits.

We introduce a quantum memory using a novel niobium cavity controlled by a weakly-coupled transmon ancilla. We show that a single-photon qubit encoded in the cavity achieves lifetimes an order of magnitude beyond the current state of the art [1]. Furthermore, we present a protocol that effectively suppresses ancilla errors propagating to the cavity, and demonstrate the effect of this procedure on the coherence time of bosonic qubits.

[1] O. Milul, B. Guttel et al., PRX Quantum 4, 030336 (2023).