Dual-rail encoding with superconducting cavities

Erasure qubits are an attractive paradigm for quantum error correction whereby most physical errors are detected and thus known to occur at a particular qubit location. We propose using the dual-rail encoding with superconducting cavities to realize an erasure qubit and describe a complete set of necessary hardware operations [1]. We coin this qubit the “dual-rail cavity qubit”. Much like its equivalent in quantum optics, the physical qubit is encoded in the single photon subspace of two bosonic modes. However, the non-linearities afforded by circuit quantum electrodynamics now allow for direct entangling gates and non-destructive error-detection. With the addition of a dispersively coupled transmon, we can realize a universal gate-based set of operations on our dual-rail cavity qubits that maintain the desired properties of erasure qubits. The dominant hardware errors arising from both the transmon and cavities are detectable with high probability, allowing us to treat them as erasure errors. With today’s coherence times, we expect the dual-rail cavity qubit to operate far below the relevant QEC thresholds.

[1] Teoh et al. PNAS 2023