Coherence Properties of Shallow Donor Qubits in ZnO

Defects in crystals are leading candidates for photon-based quantum technologies, but progress in developing practical devices critically depends on improving defect optical and spin properties. Motivated by this need, we study a new defect qubit candidate, the shallow donor in ZnO. We demonstrate all-optical control of the electron spin state of the donor qubits and measure the spin coherence properties. We find a longitudinal relaxation time T-1 exceeding 100 ms, an inhomogeneous dephasing time T-2(*) of 17 +/- 2 ns, and a Hahn-spin-echo time T-2 of 50 +/- 13 mu s. The magnitude of T-2(*) is consistent with the inhomogeneity of the nuclear hyperfine field in natural ZnO. Possible mechanisms limiting T-2 include instantaneous diffusion and nuclear spin diffusion (spectral diffusion). These dephasing mechanisms suggest that with isotope and chemical purification qubit coherence times can be extended. This work should motivate further research on high-purity material growth, quantum-device fabrication, and high-fidelity control of the donor-ZnO system for quantum technologies.