Ensemble spin relaxation studies of shallow donor qubits in ZnO*

Neutral shallow donor qubits in ZnO, such as Al, Ga, and In substituting for Zn, are a promising new spin-qubit platform for quantum technologies such as hybrid quantum networks [1]. In previous work, we have demonstrated optical spin initialization, spin relaxation times (T₁) of 140 μs, spin-echo coherence times (T₂) of 50 μs and narrow inhomogeneously broadened linewidths of ≈25 GHz [2]. Here, we will present an experimental and theoretical study of the longitudinal spin relaxation of electrons bound to neutral shallow Ga donors. Experimentally, an inverse power dependence on magnetic field is observed, with T₁ ranging from 1 ms to 480 ms over 7 T to 1.75 T. Experimental results are compared to a theoretical model which suggests that the spin relaxation is mediated by the phonon emission/absorption in the presence of spin-orbit coupling (admixture mechanism). We additionally find an effect of the excitation energy on T₁. The experimental data suggest additional mechanisms that (a) soften the magnetic field dependence at high fields and (b) speed up the relaxation process with varying donor densities.

[1] Jennifer F. Lilieholm, et. al., Appl. Phys. Let. 117 (2020),

[2] Xiayu Linpeng, et. al., Phys. Rev. Applied 10, 064061 (2018).