Fluorescence spectrum and charge state control of divacancy qubits via illumination at elevated temperatures in 4H silicon carbide

Abstract

Divacancy in its neutral charge state (${\mathrm{V}}_{\text{C}}{\mathrm{V}}_{\text{Si}}^{0}$) in 4H silicon carbide (SiC) is a leading quantum bit (qubit) contender. Owing to the lattice structure of 4H SiC, four different ${\mathrm{V}}_{\text{C}}{\mathrm{V}}_{\text{Si}}$ configurations can be formed. The ground and the optically accessible excited states of ${\mathrm{V}}_{\text{C}}{\mathrm{V}}_{\text{Si}}^{0}$ configurations exhibit a high-spin state, and the corresponding optical transition energies are around $\ensuremath{\approx}1.1\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ falling in the near-infrared wavelength region. Recently, photoluminescence (PL) quenching has been experimentally observed for all ${\mathrm{V}}_{\text{C}}{\mathrm{V}}_{\text{Si}}$ configurations in 4H SiC at cryogenic temperatures. It has been shown that ${\mathrm{V}}_{\text{C}}{\mathrm{V}}_{\text{Si}}^{0}$ is converted to ${\mathrm{V}}_{\text{C}}{\mathrm{V}}_{\text{Si}}^{\ensuremath{-}}$ and it remains in this shelving dark state at cryogenic temperatures until photoexcitation with the threshold energies or above is applied to convert ${\mathrm{V}}_{\text{C}}{\mathrm{V}}_{\text{Si}}^{\ensuremath{-}}$ back to ${\mathrm{V}}_{\text{C}}{\mathrm{V}}_{\text{Si}}^{0}$. In this study, we demonstrate both in experiments and theory that the threshold energy for reionization is temperature dependent. We carry out density functional theory (DFT) calculations in order to investigate the temperature dependent reionization spectrum, i.e., the spectrum of the ${\mathrm{V}}_{\text{C}}{\mathrm{V}}_{\text{Si}}^{\ensuremath{-}}\ensuremath{\rightarrow}\phantom{\rule{4pt}{0ex}}{\mathrm{V}}_{\text{C}}{\mathrm{V}}_{\text{Si}}^{0}$ process. We find that simultaneous optical reionization and qubit manipulation can be carried out at room temperature with photoexcitation at the typical excitation wavelength used for readout of the divacancy qubits in 4H SiC, in agreement with our experimental data. We also provide the analysis of the PL spectrum of ${\mathrm{V}}_{\text{C}}{\mathrm{V}}_{\text{Si}}^{0}$, characteristic for each ${\mathrm{V}}_{\text{C}}{\mathrm{V}}_{\text{Si}}^{0}$ configuration in 4H SiC, using the Huang-Rhys theory, and find that one configuration in 4H SiC stands out in terms of the strength of coherent emission among the four configurations.