Neutral VC defect qubit in two-dimensional hexagonal GeC monolayer

The controlled realization of defect-based qubits in two-dimensional (2D) semiconductors is crucial for scalable quantum information and sensing technologies. Using first-principles calculations, we identify 2D germanium carbide (GeC) monolayer as a viable host material for defect qubits. The GeC monolayer exhibits excellent dynamical and thermodynamic stability, a wide bandgap of 2.97 eV, and weak spin–orbit coupling. A systematic study of vacancy, substitutional, and antisite defects shows that the neutral carbon vacancy (VC0) possesses a stable spin-triplet ground state (S=1) and preserves spin conservation during optical excitation, with a total magnetic moment of 2.0μB. Charge-transition analysis indicates that VC0 remains thermodynamically stable across a wide Fermi level range. At the HSE06 level, its zero-phonon line is located at 0.96 eV in the near-infrared region, while the zero-field splitting parameter lies in the microwave regime, enabling coherent optical and microwave spin control. These results establish carbon vacancy centers in GeC monolayer as promising 2D solid-state qubit candidates.