Room-temperature high-speed nuclear-spin quantum memory in diamond

Quantum memories provide intermediate storage of quantum information until it is needed for the next step of a quantum algorithm or a quantum communication process. Relevant figures of merit are therefore the fidelity with which the information can be written and retrieved, the storage time, and also the speed of the read-write process. Here, we present experimental data on a quantum memory consisting of a single C-13 nuclear spin that is strongly coupled to the electron spin of a nitrogen-vacancy (NV) center in diamond. The strong hyperfine interaction of the nearest-neighbor carbon results in transfer times of 300 ns between the register qubit and the memory qubit, with an overall fidelity of 88% for the write-storage-read cycle. The observed storage times of 3.3 ms appear to be limited by the T-1 relaxation of the electron spin. We discuss a possible scheme that may extend the storage time beyond this limit. DOI: 10.1103/PhysRevA.87.012301