Design of Two-Level Quantum state in 2D Materials for Single Photon Emission

Due to reduced dimensionality, defect levels in two-dimensional (2D) semiconductors are often far away from band edges, making 2D semiconductors ideal systems for single photon emission (SPE), if they can host defects forming a two-level quantum state. Recently, SPE was experimentally observed in different 2D materials. However, the defect centers serving as sources for SPE are yet to be identified and the possible mechanism for the formation of the ideal two-level quantum state is yet to be uncovered. Here, using first-principles calculations and group theory analysis we highlight the advantages of 2D materials as host systems and also identify and design defects in various 2D materials for SPE. A generalized strategy is proposed to design defect complex by adding a paramagnetic impurity next to a vacancy defect, which forms an ideal two-level quantum system. The electronic states of the designed defect complex are well isolated from the host band edges, belong to a majority spin eigenstate, and can be controllably excited by x-polarized light, thereby satisfying all the criteria required for an ideal SPE. The defect complex is thermodynamically stable, and appears feasible for experimental realization, to serve as an SPE-source, essential for quantum computing.