Giant titanium electron wave function in gallium oxide: A potential electron-nuclear spin system for quantum information processing

The hyperfine interactions of the unpaired electron with eight surrounding ⁶⁹Ga and ⁷¹Ga nuclei in Ti-doped β-Ga₂O₃ were analyzed by electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectroscopies. They are dominated by strong isotropic hyperfine couplings due to a direct Fermi contact interaction with Ga nuclei in octahedral sites of rutile-type chains oriented along b axis, revealing a large anisotropic spatial extension of the electron wave function. Titanium in β-Ga₂O₃ is thus best described as a diffuse (Ti⁴⁺-e^-) pair rather than as a localized Ti³⁺. Both electron and ⁶⁹Ga nuclear spin Rabi oscillations could be observed by pulsed EPR and pulsed ENDOR, respectively. The electron spin decoherence time is about 1 μs (at 4 K) and an upper bound of 520 μs (at 8 K) is estimated for the nuclear decoherence time. Thus, β-Ga₂O₃:Ti appears to be a potential spin-bus system for quantum information processing with a large nuclear spin quantum register.