The quantum properties of nitrogen-vacancy $\left({\mathrm{NV}}^{-}\right)$ centers in diamond have laid the foundation for solid-state quantum bit (qubit) applications. However, as the demand for quantum computing and communication grows, the exploration of new materials has become essential. In recent years, two-dimensional (2D) materials have shown tremendous potential in qubit research due to their rich quantum phenomena, high tunability, and ease of integration. In this study, based on first-principles calculations, we propose that 2D $1T$-phase ${\mathrm{SnO}}_2$ monolayer is an experimentally viable qubit host material. With an ultrawide band gap of 4.11 eV, $1T\text{−}{\mathrm{SnO}}_2$ monolayer exhibits phosphorus-oxygen $\left({\mathrm{P}}_{\text{O}}\right)$ defects that possess stable spin doublet $(S=1/2)$ and spin triplet $(S=1)$ ground states, which are preserved during optical excitation—a critical requirement for qubit functionality. Our calculations show that ${\mathrm{P}}_{\text{O}}^0$ and ${\mathrm{P}}_{\text{O}}^{+1}$ defects are stable within a Fermi level range of 0 to 2.88 eV. Their zero-phonon lines (ZPL) of 0.65 and 0.52 eV, respectively, fall within the infrared region, making them suitable for optical detection and microwave control. The dimensional reduction in 2D $1T\text{−}{\mathrm{SnO}}_2$ monolayer is predicted to weaken the hyperfine interaction, improving qubit performance. The ${\mathrm{P}}_{\text{O}}$ defect centers in ${\mathrm{SnO}}_2$ provide a promising solution for solid-state qubit applications. Future experimental studies are expected to validate these theoretical predictions, offering important support for the advancement of quantum computing and communication technologies.

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• Defects
• Electronic structure
• 2-dimensional systems
• Qubits
• Density functional calculations