SYMMETRY-ENABLED DISCOVERY OF QUANTUM DEFECTS IN TWO-DIMENSIONAL MATERIALS

Abstract

Quantum revolution has a great potential to impose massive impact on information technology. Point defects in solid-state materials such as NV center in diamond have been demonstrated to be promising qubit candidates. Defect levels in band gaps are analogous to molecular orbitals, serving as an excellent platform for quantum applications. Atomically thin two-dimensional materials are under the spotlight in recent years, as the sheet-like geometry brings advantages for operations of quantum defects. That includes the realization of patterned qubit fabrication, operation at room temperature, and improvement of coherence time through a highly-efficient isotope purification process. Although using point defects in 2D materials is a promising route toward quantum applications, searching for viable defects satisfying the criteria of magneto-optical properties for quantum applications is challenging. Thanks to the continued development of density functional theory, sophisticated multi-electron systems can be accurately simulated on the atomistic level to evaluate multiple ground-state properties, including total energy, magnetic polarization, and atomic orbitals. In addition to that, implementing constrained DFT renders the insight of excited-state properties. Benefited from the application of data-science tools in material science, we are now capable of performing data-driven analysis based on high-throughput computational techniques, including data mining/storage and automatic discovery workflow. Adopting the above tools and physical-principle-enabled symmetry analysis, we are able to identify a large set of quantum defects in a vast material space. We show that antisite defects in 2D transition metal dichalcogenides (TMDs) can provide a general platform for controllable solid-state spin qubit systems. Using high-throughput atomistic simulations that are enabled by a symmetry-based hypothesis, we identify several neutral antisite defects in TMDs that create defect levels deep in the bulk band gaps and host a paramagnetic triplet ground state. Our in-depth analysis reveals the presence of optical transitions and triplet-singlet intersystem crossing processes for fingerprinting these defect qubits. Finally, as an illustrative example, we discuss the initialization and readout principles of an antisite qubit in WS2, which is expected to be stable against interlayer interactions in a multilayer structure for qubit isolation and protection in future qubit-based devices. Motivated by the insight gained from the study of antisite defect qubits in TMDs, we significantly expanded the searching domain to all the binary 2D materials. As mentioned above, searching for defects with triplet ground states is one of the most crucial steps to identify more quantum defects that support multiple quantum functionalities. We design a comprehensive workflow for screening promising quantum defects based on the site-symmetry-based hypothesis. The discovery efforts reveal that the symmetry-enabled discovery workflow of quantum defects significantly increases the probability of finding triplet defects. To identify multiple functionalities for these quantum defects, including qubits and quantum emitters, the magneto-optical properties of triplet defects are comprehensively calculated. We demonstrate that 45 antisite defects in the various hosts, including post-transition metal monochalcogenides (PTMCs) and transition metal dichalcogenides (TMDs) are promising quantum defects. Most importantly, we propose that 16 antisites (both anion and cation based) in PTMCs can serve as the most promising quantum defect platform based on 2D materials, due to their well-defined defect levels, optimal magneto-optical properties, and the availability of host materials. This set of data-driven discovery efforts opens a new pathway for creating scalable, room-temperature spin qubits in 2D materials, including TMDs, PTMCs, and beyond. The comprehensive defect data created in this work, combined with experimental verification and demonstration in the future, will eventually lead to the fertilization of a 2D defect design platform that facilitates the design of point defects in 2D material families for multiple quantum functionalities, including quantum emitters, quantum sensor, transductor, and more.