Vibronic States and Their Effect on the Temperature and Strain Dependence of Silicon-Vacancy Qubits in 4H-SiC

Silicon-vacancy qubits in silicon carbide (SiC) are emerging tools in quantum-technology applications due to their excellent optical and spin properties. In this paper, we explore the effect of temperature and strain on these properties by focusing on the two silicon-vacancy qubits, V1 and V2, in 4H-SiC. We apply density-functional theory beyond the Born-Oppenheimer approximation to describe the temperature-dependent mixing of electronic excited states assisted by phonons. We obtain a polaronic gap of around 5 and 22 meV for the V1 and V2 centers, respectively, which results in a significant difference in the temperature-dependent dephasing and zero-field splitting of the excited states, which explains recent experimental findings. We also compute how crystal deformations affect the zero-phonon line of these emitters. Our predictions are important ingredients in any quantum applications of these qubits sensitive to these effects.Funding Agencies|National Excellence Program of Quantum-Coherent Materials Project (Hungarian NKFIH Grant) [KKP129866]; European Union QuantERA Q-Magine Project [127889]; QuantERA Nanospin Project [127902]; European Union Horizon 2020 Quantum Technology Flagship project ASTERIQS [820394]; National Quantum Technology Program [2017-1.2.1NKP-2017-00001]; Swedish Research CouncilSwedish Research Council [VR 2016-04068]; Swedish Energy AgencySwedish Energy Agency [43611-1]; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation [KAW 2018.0071]; European Union Horizon 2020 project QuanTELCO [862721]; Japan Society for the Promotion of ScienceMinistry of Education, Culture, Sports, Science and Technology, Japan (MEXT)Japan Society for the Promotion of Science [JSPS KAKENHI 17H01056, JSPS KAKENHI 18H03770]; U.S. Department of Energy, Office of ScienceUnited States Department of Energy (DOE) [DE-SC0019174]; Swedish National Infrastructure for Computing at the National Supercomputer Centre [SNIC 2019/3667, LiU-2015-00017-60]