Coherence properties of shallow donor qubits in ZnO

TL;DR

This study investigates shallow donor defects in ZnO as potential qubits, demonstrating optical control and measuring coherence times, with results comparable to silicon donors, highlighting their promise for quantum technology applications.

Contribution

The paper introduces shallow donor defects in ZnO as a new qubit candidate, demonstrating optical control and coherence measurements, advancing the understanding of their quantum properties.

Findings

Longitudinal relaxation time T₁ exceeds 100 ms

Inhomogeneous dephasing time T₂* is 17±2 ns

Hahn spin-echo time T₂ is 50±13 μs

Abstract

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 $17\pm2$ ns, and a Hahn spin-echo time T$_2$ of $50\pm13$ $\mu$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 results are comparable to the phosphorous donor system in natural silicon, suggesting that with isotope and chemical purification long qubit coherence times can be obtained for donor spins in a direct band gap semiconductor. This work motivates further research on high-purity material growth, quantum device fabrication, and high-fidelity control of the donor:ZnO system for quantum technologies.