Probing the Evolution of Electron Spin Wavefunction of the Nitrogen Vacancy (NV) Center in diamond via Pressure Tuning*

The wavefunction of a qubit precisely encodes information about itself, including the distribution of its spin density and the contribution of the characteristic orbitals. Understanding the profile of a qubit's wavefunction is key to its quantum applications. Unlike conducting systems, however, there is no direct method for solid-state-defect based qubits in wide-bandgap semiconductors. Here, we use pressure as a tuning method and a nuclear spin as an atomic scale probe to monitor the hyperfine structure of negatively charged nitrogen vacancy (NV) centers in diamonds under pressure. By examining the ¹³C hyperfine interaction upon pressurizing, we show an increase in the NV electron spin density and rehybridization from sp³ to sp² bonds. These can be explained by the reduction of the cell size and the self-distortion of the NV center. The ab initio calculations of strain dependence of the NV center's hyperfine levels are done independently to confirm our observations. Meanwhile, the small portable pressure device can provide an isolated effect for systematic studies that require a strong lattice tuner. Furthermore, this method can be adopted to probe the evolution of wavefunction in other defect systems. This potential capability could play an important role in developing magnetometry and quantum information processing using the defect centers.