Optical Properties of Vacancy-Related Qubit Centers in SiC

Vacancy-related color centers in silicon carbid represent quantum bits or can be employed as single photon emitters. The excited defect states and the photons emitted in transitions between them and the groundstate alongside spin-selective, non-radiative transitions via intermediate low-spin states are pivotal parts of the mechanism underlying qubit applications. Optical excitation of the qubit may also lead to an ionization into other charge states in which the qubit is silent. The ability to control and deliberately switch the charge state is pivotal for applications and has recently been explored experimentally for qubit centers in SiC [1, 2]. However, the charge states actually involved in the switching and their optical properties are often not clear. Furthermore the electrical detection of spin states, as demonstrated for the NV-center in diamond[3], involves emission of defect spins into the conduction or valence band in a two-photon process. How the optical ionization yield and the spin contrast depend on the photon energy is an open question.<br/>Here we investigate the optical ionization of the divacancy, the silicon vacany and other vacancy-related color centers in SiC within the frame work of the CI-CRPA approach [4]. This approach allows for the embedded description of highly correlated multiplet states, such as the important low spin states. We shine light onto ionizing single and two-photon processes relevant for optical charge state switching and electrical detection of the spin states. Our results show that an enhanced ionization cross section can occur for photon energies well above the ionization thresholds. This determines the charge state yielded by the ionization once the ionization threshold of competing ionization channels are overcome.<br/><br/>D. A. Golter and C. W. Lai, Sci. Reports 7, 13406 (2017).<br/>G. Wolfowicz, et al., Nat. Comm. 8, 1876 (2018).<br/>E. Bourgeois et al., Nat. Comm. 6, 8577 (2015).<br/>M. Bockstedte, F. Schütz, Th. Garratt, V. Ivady, A. Gali, njp Quantum Materials 3, 31 (2018).