A Dual-rail Qubit with Parametrically Coupled Transmons

Quantum error correction (QEC) is crucial to developing fault-tolerant quantum computers. Different physical platforms are working towards error rates below the surface code threshold. A new promising approach seeks to convert certain environmentally-induced state transitions into so-called qubit "erasures". These erasure errors can be monitored directly without destroying the qubit's entangled state, and can be discarded, requiring no further correction. The concept behind our erasure qubit relies on using the single-photon subspace of two parametrically coupled transmons as the logical qubit. This allows the conversion of dominant thermal relaxation errors, leakage out of computational subspace, to erasure errors. This system forms a "dual-rail" encoding, using two transmons where arbitrary single qubit operations are completely controlled with microwave parametric pulses. In this talk, we will describe our system design and operation, and show how dual-rail encoding largely improves the coherence of the erasure qubit over the individual transmon qubits.