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Photoluminescence lineshapes and charge state control of divacancy qubits in silicon carbide

Divacancy in its neutral charge state (V$_\text{C}$V$_\text{Si}^0$) in 4H silicon carbide (SiC) is a leading quantum bit (qubit) contender. Owing to the lattice structure of 4H SiC four different V$_\text{C}$V$_\text{Si}$ configurations can be formed. Ground and optical excited states of V$_\text{C}$V$_\text{Si}^0$ exhibit $S$=1 spintriplet state and the corresponding transition energies are around $\approx 1.1$~eV falling in the near-infrared wavelength region. Recently, photoluminescence (PL) quenching has been experimentally observed for all V$_\text{C}$V$_\text{Si}$ configurations in 4H SiC, i.e. the corresponding zero-phonon lines (ZPLs) appear only at higher-than-ZPL photoexcitation energies (threshold energies). It has been shown that V$_\text{C}$V$_\text{Si}^0$ is converted to V$_\text{C}$V$_\text{Si}^-$ upon photoexcitation below the correspoding excitation threshold energies at cryogenic temperature, i.e. V$_\text{C}$V$_\text{Si}^-$ is the so-called dark state. In this study we demonstrate that the threshold energy for reinozation is temperature dependent. We further carry out density functional theory (DFT) calculations in order to investigate the temperature dependent reionization spectrum, i.e. the spectrum of the V$_\text{C}$V$_\text{Si}^- \rightarrow$ V$_\text{C}$V$_\text{Si}^0$ process and found that simultaneous reionization and qubit manipulation can be carried out at around room temperature ($\approx$300~K) by using the usually applied excitation wavelength. We also investigate the PL lineshape of V$_\text{C}$V$_\text{Si}^0$ by using the Huang-Rhys theory.