Degeneracy-preserving quantum non-demolition measurement of parity-type observables for cat-qubits

Understand

A central requirement for any quantum error correction scheme is the ability to perform quantum non-demolition measurements of an error syndrome, corresponding to a special symmetry property of the encoding scheme.

• It is in particular important that such a measurement does not introduce extra error mechanisms, not included in the error model of the correction scheme.
• In this letter, we ensure such a robustness by designing an interaction with a measurement device that preserves the degeneracy of the measured observable.
• More precisely, we propose a scheme to perform continuous and quantum non-demolition measurement of photon-number parity in a microwave cavity.