Ab Initio Design of Quantum Defects in 2D Transition Metal Dichalcogenides, 2D and 3D Oxides

Quantum defects in solid-state materials are emerging as promising candidates for scalable quantum information systems, with the potential to be integrated seamlessly with conventional semiconductor electronic devices. While prototype quantum defects, such as nitrogen-vacancy (NV^-) center in diamond, have paved the way for optically addressable spin qubits, challenges remain in achieving precise positioning and tunable properties. In this talk, I will report an ab initio approach to design quantum defects in two-dimensional (2D) materials, focusing on transition metal dichalcogenides (TMDs) and 2D silicon oxide, which may enable the controlled positioning of quantum defects. Our previous first-principles investigations of TMDs reveal a family of quantum defects, where transition metal atoms substituted at chalcogen sites exhibit spin-triplet ground states, strong optical transitions in the telecom band, and zero-field splitting in the tens of GHz.[1] These properties make them promising candidates for spin qubits with potential for scalable quantum information processing. We further investigate the feasibility of creating these defects via controlled manipulation using scanning tunneling microscopy (STM) tip, demonstrating a pathway for precise defect positioning and fabrication. To pursue longer coherence time, we extend our study to 2D silicon oxide with tetrahedral Si-O crystal field units, identifying single-photon emitters and spin-defect qubits with favorable electronic and magnetic properties. These defects, including Cr_Si and Mo_Si substitutions in SiO₂, exhibit promising zero-phonon transitions and intersystem crossing rates, placing oxides as superior candidates compared to other 2D materials for quantum technologies. Compared to 2D silica bilayer, 3D silicon oxides exhibit many different phases, but are predominantly composed of tetrahedral Si-O crystal field units. Building on our work in 2D silica bilayer, I will also present our investigation into the more complex Si-based 3D oxides, such as CaSiO₃, CeSiO₄, and Ca₂SiO₄, highlighting their potential as hosts for advanced quantum defects. Our work offers a new route to the development of hybrid classical-quantum systems. By leveraging ab initio design principles, we provide insights into defect formation, control, and integration, opening the door to future quantum communication and computation applications.

Acknowledgements. This work was supported by This research was supported by National R&D programs through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (2022M3H4A3052556 and 2022M3H4A1A04096496), Republic of Korea.

[1] Lee, Yeonghun, Yaoqiao Hu, Xiuyao Lang, Dongwook Kim, Kejun Li, Yuan Ping, Kai-Mei C. Fu, and Kyeongjae Cho, "Spin-defect qubits in two-dimensional transition metal dichalcogenides operating at telecom wavelengths." Nature Communications 13 (1), 7501 (2022).