Deterministic generation of a twin-Fock state of two nitrogen-vacancy ensembles via a superconducting flux qubit

The twin-Fock state plays a central role in quantum metrology and quantum information processing. Here, we propose a method to generate a twin-Fock state of two nitrogen-vacancy-center (NV) ensembles using a superconducting flux qubit. This state is deterministically prepared by simultaneously exciting two NV ensembles with the flux qubit. Numerical simulations demonstrate that twin-Fock states with n⩽6 can be prepared with high fidelity using current experimental technology. This proposal is universal and can be employed with other solid-state devices coupled to a superconducting qubit.