A single-atom quantum memory in silicon

Long coherence times and fast gate operations are desirable but often conflicting requirements for physical qubits. This conflict can be resolved by resorting to fast qubits for operations, and by storing their state in a ‘quantum memory’ while idle. The 31P donor in silicon comes naturally equipped with a fast qubit (the electron spin) and a long-lived qubit (the 31P nuclear spin), coexisting in a bound state at cryogenic temperatures. Here, we demonstrate storage and retrieval of quantum information from a single donor electron spin to its host phosphorus nucleus in isotopically enriched 28Si. The fidelity of the memory process is characterised via both state and process tomography. We report an overall process fidelity F p ≈ 81 %, and memory storage times up to 80 ms. These values are limited by a transient shift of the electron spin resonance frequency following high-power radiofrequency pulses.