Long coherence times and fast gate operations are desirable but oftenconflicting requirements for physical qubits. This conflict can be resolved byresorting to fast qubits for operations, and by storing their state in a`quantum memory' while idle. The $^{31}$P donor in silicon comes naturallyequipped with a fast qubit (the electron spin) and a long-lived qubit (the$^{31}$P nuclear spin), coexisting in a bound state at cryogenic temperatures.Here, we demonstrate storage and retrieval of quantum information from a singledonor electron spin to its host phosphorus nucleus in isotopically-enriched$^{28}$Si. The fidelity of the memory process is characterised via both stateand process tomography. We report an overall process fidelity of $F_p=$81${\pm}$7%, a memory fidelity ($F_m$) of over 90%, and memory storage timesup to 80 ms. These values are limited by a transient shift of the electron spinresonance frequency following high-power radiofrequency pulses.
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