Theory of strained quantum emitters

Defects in semiconductors acting as optically active spin qubits are intriguing objects of fundamental study and future technological developments. These defect-based color centers are of particular interest for detection and response to physical variations such as pressure and strain. To investigate the defect emission response to strain, we have studied the vibrational structure of the negatively charged silicon vacancy ($\mathrm{V_{Si}^{-}}$) in 4H-SiC under applied tensile and compressive uniaxial strain using first-principles calculations. The strain variations of the emission spectrum can be explained by differing responses of bulk-like and quasi-localized vibrational modes. In particular, substantial differences are found between the hexagonal ($h$) and quasicubic ($k$) configurations of $\mathrm{V_{Si}^{-}}$ in 4H-SiC that result in a strain-induced improvement of the Debye-Waller factor for $\mathrm{V_{Si}^{-}}(h)$ under $+2\%$ uniaxial strain along the $a$-axis of 4H-SiC. Finally, strain-dependent changes in the phonon sideband enable distinguishing between compressive and tensile strain, opening up the possibility of magnetic field-free strain detection using only spin-conserving transitions of solid-state quantum emitters.