Protected C-Parity Qubits Part 1: Characterization and Protection

Superconducting qubits with topological protection against local noise hold the promise of significantly enhanced coherence times and higher gate fidelities than is possible with conventional qubits. We are developing one such protected design — the hybrid charge-parity qubit — that combines arrays of compact, high inductances and conventional Josephson junctions with individual flux control for tuning each plaquette to a regime with a π-periodic Josephson energy. With this scheme, concatenating multiple π-periodic elements further enhances the degree of protection. Here, we will describe our experimental characterization of devices with concatenated π-periodic elements through spectroscopy and time-domain measurements.