Properties of Si vacancies in SiC
Silicon vacancy centers in silicon carbide (SiC) have attractive optical and spin properties.
The vacancy formed by a missing silicon atom is tetragonally surrounded by four carbon atoms.
We are focusing on the vacancy centers in the 6H-SiC polytype, where three inequivalent Si vacancies exist.
The so-called V1 and V3 vacancies are located at cubic sites, V2 at a hexagonal site.
In the negatively charged state, all centers have spin 3/2.
Laser irradiation of the sample generates strong spin polarisation and measurement of the photoluminescence
can be used for optically detected magnetic resonance.
Multi-photon spin transitions in Si vacancies
Under typical experimental conditions, the Rabi frequencies of this system are comparable to the transitions frequencies.
As a result, the rotating wave approximation that is typically used to describe magnetic resonance experiments can break down.
The dynamics of the system becomes aperiodic but can, within some bounds, be described as a combination of multi-photon transition
where multiple RF photons drive allowed or forbidden transitions in the spin-3/2 system.
The results of ODMR measurements can be consistently interpreted with the help of numerical simulations that do not rely on the rotating wave approximation.
 Experimental characterization of spin-3/2 silicon vacancy centers in 6H-SiC
H. Singh, A. N. Anisimov, S. S. Nagalyuk, E. N. Mokhov, P. G. Baranov and D. Suter
Phys. Rev. B 101, 134110 (2020)
 Optical spin initialization of spin-3/2 silicon vacancy centers in 6H SiC at room temperature
H. Singh, A. N. Anisimov, I. D. Breev, P. G. Baranov and D. Suter
Phys. Rev. B 103, 104103 (2021)
 Relaxation processes and high-field coherent spin manipulation in color center ensembles in 6H-SiC
V. A. Soltamov, B. V. Yavkin, A. N. Anisimov, H. Singh, A. P. Bundakova, G. V. Mamin, S. B. Orlinskii, E. N. Mokhov, D. Suter and P. G. Baranov
Phys. Rev. B 103, 195201 (2021)
 Multi-photon multi-quantum transitions in the spin-3/2 silicon-vacancy centers of SiC
Harpreet Singh, Alex Mario Hollberg, Andrei N. Anisimov, Pavel G. Baranov and Dieter Suter.
Phys. Rev. Research 4, 023022 (2022)
 Inverted fine structure of a 6H-SiC qubit enabling robust spin-photon interface
I. D. Breev, Z. Shang, A. V. Poshakinskiy, H. Singh, Y. Berencén, M. Hollenbach, S. S. Nagalyuk, E. N. Mokhov, R. A. Babunts, P. G. Baranov, D. Suter, S. A. Tarasenko, G. V. Astakhov, A. N. Anisimov.
npj Quantum Information 8, 23 (2022)