Error-correctable microwave dual-rail qubits

Dual-rail qubits represent a promising platform for fault-tolerant quantum technologies since their ability to convert leakage errors to erasure allows a reduced error threshold when embedding them in an outer code. In conventional encodings based on a single excitation shared between two modes, a single damping error leads to leakage, which needs an outer code to be corrected. Using multi-photon codewords, one can in principle avoid this limitation and correct damping errors on a single dual-rail qubit. I will outline the control of such multi-photon dual-rail qubits with a focus on the four-photon variant. In particular, I will discuss qubit initialization, available quantum gates and how they can be used to implement arbitrary one- and two-qubit operations, measurements to detect errors and determine the logical state, and error correction operations. I will then briefly lay out the challenges when scaling to dual-rail qubits with higher photon numbers. With the ability to correct the dominant error, the multi-photon dual-rail encodings have the potential to greatly reduce the size of the outer code needed for fault-tolerant quantum operation.