Coherent Spin Preparation of Indium Donor Qubits in Single ZnO Nanowires

Neutral shallow donors in ZnO, such as impurities substituting on a Zn site, are promising candidates for photon-mediated quantum technologies. Here, we will focus on the indium donor in isolated ZnO nanowires. Compared to bulk ZnO, isolated nanowires offer a promising avenue to isolate few/single donors. Moreover, nanostructures can be used for photonic device integration. We show that favorable donor-bound exciton optical and electron spin properties are retained in isolated ZnO nanowires. The inhomogeneous optical linewidth of small ensembles of indium donors in single nanowires (60 GHz) is within a factor of 2 of what is found for single-crystalline bulk ZnO. In isolated ZnO nanowires, spin initialization via optical pumping is demonstrated and coherent population trapping is observed. The two-photon absorption width approaches the theoretical limit expected due to the strong hyperfine interaction between the indium nuclear spin and the donor-bound electron. Notably, the strong hyperfine interaction observed for indium donors with a nuclear spin of 9/2 paves the way for qubit registers in ZnO with potential applications in quantum memories.