Experimental implementation of pair-cat code with superconducting microwave circuits (2/2)*

Stabilized quantum manifolds of a bosonic system can encode error-protected qubits. In particular, a logical qubit encoded in a single-mode manifold spanned by cat states is exponentially protected against phase-flip errors. However, in existing experimental implementations with microwave superconducting circuits, detecting and fully correcting photon-loss errors is challenging without turning off the dissipative stabilization process. On the other hand, a phase-flip error protected logical qubit can be encoded in a stabilized manifold spanned by pair-cat states, which are superpositions of two-mode states called Barut-Girardello/pair-coherent states. Advantageously, photon loss errors in either mode can be detected by monitoring the photon-number difference between them, without stopping manifold stabilization.

Part-two of this two-part presentation will introduce the experimental design of pair-coherent states with superconducting microwave cavity system and present recent results.