Hydrostatic deformation is an effective approach for tuning the quantum properties of color centers in diamond, with significant implications for quantum sensing, computing, and communication. Compared to the widely studied nitrogen-vacancy (NV) centers, silicon-vacancy (SiV) centers exhibit more than a tenfold increase in coherent photon emission. In this work, we investigate the effects of hydrostatic pressure and tension on the SiV center in diamond using first-principles calculations with the r2SCAN meta-GGA (Generalized Gradient Approximation) functional. We demonstrate that under hydrostatic tension corresponding to an isotropic expansion exceeding 4%, the SiV center undergoes spontaneous symmetry breaking from the inversion-symmetric D3d structure to the asymmetric C3v configuration, similar to that of the NV center. Within the hydrostatic compression and tension range corresponding to isotropic deformations of −8%–4%, the optical properties and hyperfine parameters of the SiV center change monotonically, indicating promising potential for pressure- or deformation-sensing applications. A microscopic explanation of these trends is provided from an electronic structure perspective. The r2SCAN meta-GGA functional shows high accuracy in calculating hyperfine parameters, in agreement with experimental results. This study enhances our understanding of the optical properties and hyperfine interactions of SiV defects in diamond, laying the groundwork for their potential use in hydrostatic pressure or strain sensing applications.
Hydrostatic deformation is an effective approach for tuning the quantum properties of color centers in diamond, with significant implications for quantum sensing, computing, and communication. Compared to the widely studied nitrogen-vacancy (NV) centers, silicon-vacancy (SiV) centers exhibit more than a tenfold increase in coherent photon emission. In this work, we investigate the effects of hydrostatic pressure and tension on the SiV center in diamond using first-principles calculations with the r2SCAN meta-GGA (Generalized Gradient Approximation) functional. We demonstrate that under hydrostatic tension corresponding to an isotropic expansion exceeding 4%, the SiV center undergoes spontaneous symmetry breaking from the inversion-symmetric D3d structure to the asymmetric C3v configuration, similar to that of the NV center. Within the hydrostatic compression and tension range corresponding to isotropic deformations of −8%–4%, the optical properties and hyperfine parameters of the SiV center change monotonically, indicating promising potential for pressure- or deformation-sensing applications. A microscopic explanation of these trends is provided from an electronic structure perspective. The r2SCAN meta-GGA functional shows high accuracy in calculating hyperfine parameters, in agreement with experimental results. This study enhances our understanding of the optical properties and hyperfine interactions of SiV defects in diamond, laying the groundwork for their potential use in hydrostatic pressure or strain sensing applications.
The neutral silicon--vacancy (SiV0) center in diamond combines inversion symmetry with optical emission, making it a robust quantum emitter resilient to stray electric fields. Using first-principles density-functional theory, we quantify its response to isotropic strain spanning strong compression and tensile regimes (effective hydrostatic pressures of approximately −80 to 180~GPa). The coexistence of doubly degenerate eg and eu levels produces a structural instability captured by a quadratic product Jahn--Teller model. Under isotropic compression, the zero-phonon line blue-shifts nearly linearly while the Eg phonon stiffens, suppressing vibronic instabilities and reducing Jahn--Teller quenching. Consequently, the Ham-reduced excited-state spin--orbit splitting increases substantially and the dark--bright vibronic gap widens. In contrast, isotropic tensile strain enhances vibronic effects and induces symmetry breaking beyond a critical strain, with tunneling-mediated dynamical averaging at the onset. Throughout the symmetry-preserving regime, parity remains well defined, so isotropic strain alone does not activate the dark transition. Charge-transition levels indicate photostability of the emission deep into the compressive regime, and near the highest photostable deformation (∼100~GPa), the radiative lifetime increases due to a reduced transition dipole moment despite the increasing optical energy. These trends yield compact calibration relations linking optical and spin observables to isotropic strain and establish SiV0 as a symmetry-protected, strain-tunable quantum emitter operating into the multi-megabar-equivalent regime.
The integration of Nitrogen-Vacancy color centers into diamond anvil cells has opened the door to quantum sensing at megabar pressures. Despite a multitude of experimental demonstrations and applications ranging from quantum materials to geophysics, a detailed microscopic understanding of how stress affects the NV center remains lacking. In this work, using a combination of first principles calculations as well as high-pressure NV experiments, we develop a complete description of the NV's optical properties under general stress conditions. In particular, our ab initio calculations reveal the complex behavior of the NV's inter-system crossing rates under stresses that both preserve and break the defect's symmetry. Crucially, our proposed framework immediately resolves a number of open questions in the field, including: (i) the microscopic origin of the observed contrast-enhancement in (111)-oriented anvils, and (ii) the surprising observation of NV contrast-inversion in certain high-pressure regimes. Our work lays the foundation for optimizing the performance of NV high-pressure sensors by controlling the local stress environment, and more generally, suggests that symmetry-breaking stresses can be utilized as a novel tuning knob for generic solid-state spin defects.
The silicon-vacancy (SiV) and nitrogen-vacancy (NV) centers in diamond are commonly regarded as prototypical defects for solid-state quantum information processing. Here, we show that when silicon and nitrogen are simultaneously introduced into the diamond lattice, these defects can strongly interact and form larger complexes. Nitrogen atoms strongly bind to Si and SiV centers, and complex formation can occur. Using a combination of hybrid density functional theory and group theory, we analyze the electronic structure and provide various useful physical properties, such as hyperfine structure, quasilocal vibrational modes, and a zero-phonon line, to enable experimental identification of these complexes. We demonstrate that the presence of substitutional silicon adjacent to nitrogen significantly shifts the donor level toward the conduction band, resulting in an activation energy for the SiN center that is comparable to phosphorus. We also find that the neutral SiNV center is of particular interest due to its photon emission at $\ensuremath{\sim}1530\phantom{\rule{0.28em}{0ex}}\mathrm{nm}$, which falls within the C band of telecom wavelengths and its paramagnetic nature. In addition, the optical transition associated with the SiNV0 color center exhibits very small electron-phonon coupling (Huang-Rhys factor = 0.78) resulting in high quantum efficiency (Debye-Waller factor = 46%) for single-photon emission. These features render this new center very attractive for a potential application in scalable quantum telecommunication networks.
The nitrogen vacancy (NV) center has emerged as a powerful quantum sensor in high-pressure research, with the observation of optically detected magnetic resonance at megabar pressures. However, some aspects of NV physics require further investigation to optimize the development of NV-based sensing under pressure. Here, we study both experimentally and theoretically the optical properties of the NV center under hydrostatic pressure. We investigate the evolution of the zero-phonon line (ZPL) position, radiative lifetimes, optical lineshapes, and photoionization thresholds of the NV center under pressures up to ~120 GPa. We also provide spectroscopic guidelines for performing high-pressure optical experiments. Our results confirm that the NV center remains a robust quantum sensor under extreme hydrostatic pressures, especially for magnetic characterization.
Diamonds and nanodiamonds (NDs) containing quantum color centers, such as nitrogen-vacancy (NV) centers, have been widely studied in recent years for their promising applications across various fields, including cryptography and telecommunications, medical sciences, and sensing. In the context of sensing, recent studies on color centers such as silicon-vacancy (SiV) and germanium-vacancy (GeV) centers have shown great potential for measuring physical quantities like magnetic fields, temperature, and strain. This is due to their intense zero-phonon line (ZPL) optical signal, which accounts for about 80% of their total luminescence and is characteristic of group-IV color centers (G4V) [1]. In our recent papers, we demonstrated that as-grown CVD NDs containing SiV and GeV centers, featuring luminescent ZPLs and excellent photostability at room temperature, can function effectively as nanosensors under high stress and pressure conditions (up to 180 GPa) [2, 3]. To advance our research, in this work we investigate the optical properties of SiV centers in as-grown NDs at cryogenic temperatures. For SiV centers, which have spin 1/2, the fine structure should become accessible through the Jahn-Teller effect, which lifts the degeneracy at cryogenic temperatures (< 20 K). However, experiments on our as-grown NDs reveal significant spectral broadening even at around 9 K, caused by lattice strain, which prevents access to the optically addressable electronic spin states of the SiV center. To overcome this limitation, we propose an original post-treatment involving high-pressure and high-temperature (HPHT) annealing using the Paris–Edinburgh press. This approach allows the gradual increase of temperature and pressure allows for control over the undesired diamond-to-graphite phase transition. HPHT annealing experiments were conducted at the PSICHE beamline of Synchrotron SOLEIL [4], where X-ray diffraction and tomography analyses enabled precise monitoring of P-T parameters and made it possible for the first time to access single fine-structure transitions of SiV centers in such NDs.References[1] C. Bradac, et al., Nat. Commun. 10, 1 (2019). [2] B. Vindolet, et al., Phys. Rev. B 106, 214109 (2022).[3] M. De Feudis, et al., Adv. Mater. Interfaces 7, 1901408 (2019).[4] L. Henry et al., J. Synchrotron Rad. 29 (2022).
The negatively charged silicon vacancy (SiV) color center in diamond has recently proven its suitability for bright and stable single photon emission. However, its electronic structure so far has remained elusive. We here explore the electronic structure by exposing single SiV defects to a magnetic field where the Zeeman effect lifts the degeneracy of magnetic sublevels. The similar responses of single centers and a SiV ensemble in a low strain reference sample prove our ability to fabricate almost perfect single SiVs, revealing the true nature of the defect's electronic properties. We model the electronic states using a group-theoretical approach yielding a good agreement with the experimental observations. Furthermore, the model correctly predicts polarization measurements on single SiV centers and explains recently discovered spin selective excitation of SiV defects.