Transition metal impurities in Silicon: Computational search for semiconductor qubit

Two classical impurity-semiconductor qubits are ³¹P in silicon and NV^- center in diamond, both of which have their own strengths and weaknesses. The spin subsystem of ³¹P in Si requires extremely low temperature to initialize while in case of the NV^- center, it is initialized by the non-radiative transition, which allows higher operating temperatures. However, diamond manufacturing is not as mature as Si. Herein, we search for candidate Si-based impurity-semiconductor qubits that could benefit from the established silicon technology but with higher operating temperature. Since transition metal impurities are known to form deep states in crystalline Si, we conduct a survey of all 3d and selected heavier transition metals using modern first-principles defect calculations with the purpose of predicting location and spin of defect levels. Specifically, we applied the well-established supercell approach and HSE06 hybrid functional, which accurately reproduces band gap of Si as well as localization of defect states. As a result, we find several candidate impurities that form spin triplet defect states within the electronic bandgap with C_3v symmetry. These candidate systems resemble the NV^- center in diamond and hold the potential to operate at higher temperature.