Hybrid entanglement and bit-flip error correction in a scalable quantum network node

Abstract

Recent efforts have succeeded in producing quantum networks in which quantum information can be stored, transferred and processed across multiple nodes on a metropolitan scale. A key remaining challenge is to enhance the capabilities of individual nodes, providing precise and robust control over multiple qubits. Here we demonstrate coherent control in a hybrid quantum node based on a diamond colour centre. We entangle three types of qubit: an electron spin as an interface qubit, a nuclear spin with long memory time and a flying photonic qubit. These qubits’ frequencies span three distinct regimes, from the optical to the radio-frequency domain. By incorporating two additional nuclear spins, we encode three memory qubits into a logical state using a repetition code and entangle this logical qubit with a photonic qubit. We repeatedly read out the error syndromes of memory qubits using the electron interface qubit, then apply real-time feedback operations to correct bit-flip errors. We perform our protocol for up to 12 rounds and demonstrate an improvement in the logical–photonic joint state population compared with its uncorrected counterpart. Our results demonstrate the feasibility of several key functionalities required for quantum repeaters to operate in full-fledged quantum networks. Nodes in a quantum network must be able to interface with photonic qubits as well as perform local quantum computations. The quantum node device presented here is capable of storing quantum information and correcting bit-flip errors.