Alice & Bob and ENS Lyon stabilize cat qubits with DC voltage bias

Alice & Bob/Cat-qubit roadmap

Alice & Bob and ENS Lyon report a way to stabilize cat qubits with a steady voltage instead of a microwave drive. The companies say it could mean more compact quantum hardware that gives off less heat inside the cryostat. The results are in a preprint that has not been peer-reviewed.

• A SQUID biased with about one millionth of a volt couples a memory resonator to a lossy buffer resonator and exchanges photons between them.
• The reported two-photon exchange rate is 3 MHz, which the companies say beats any earlier microwave-pumped coupler.
• Changing the bias switches the device between one-, two- and four-photon processes, which could support four-component cat qubits.
• The approach is presented as a complement to the existing microwave-driven method, and four-photon operation remains a future goal.