Probing the coherence of solid-state qubits at avoided crossings*

The avoided crossing of energy levels in spin defects can be both beneficial and detrimental to quantum information applications. The emergence of a clock transition enhances the protection from magnetic noise thus improving coherence times, while ground state level anti-crossings (GSLAC) can increase longitudinal relaxation rates. We investigate the dynamics of divacancy spin qubits in SiC at a clock transition and near the GSLAC using a combination of theory and experiments. We present a theoretical approach based on a generalization of the cluster expansion method. We characterize the decoherence mechanism of spin qubits at avoided crossings, the transition from quantum to classical noise, and the emergence of multiple clock transitions arising from strongly coupled nuclear spins. Combined with ab-initio predictions of spin Hamiltonian parameters, the proposed theoretical approach paves the way to designing the coherence properties of spin qubits from first principles. [1,2]

1. M. Onizhuk, K. C. Miao, J. P. Blanton, H. Ma, et al., ArXiv preprint:https://arxiv.org/abs/2010.11077
2. A. Bourassa, C.P. Anderson, K.C. Miao, M. Onizhuk, et al., Nat. Mater. 1-7 (2020)