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Silicon vacancy (SiV) centers in diamonds have attracted much attention because of their stability and narrow emission linewidth, and are promising for applications in quantum information technology. SiV-center-encapsulated nanodiamonds have also attracted much attention because of their potential to be coupled to various photonic devices. One efficient way to fabricate nanodiamonds that contain SiV centers is Si ion implantation into nanodiamonds. However, the evaluation of a single SiV center in a nanodiamond produced by this method at low temperatures has not been performed. In this study, we report on the optical properties of a single SiV center in a nanodiamond produced by ion implantation at cryogenic temperatures. The emission spectrum from a single SiV center ( $g^2(0) = 0.19$ ) was observed with four distinct fine splittings of the zero-phonon line (ZPL) at 4 K. At an excitation power of 50 $\mathrm{\mu}$ W, the full width at half maximum of the ZPL reached the spectrometer resolution limit (0.09 nm). The temperature dependence of the emission peak is consistent with that of the emission coming from an SiV center under high strain. The results obtained in this work suggest that nanodiamonds containing single SiV centers formed using this method will be an important building block for the realization of quantum information applications.

Coherent exchange of single photons is at the heart of applied quantum optics. The negatively-charged silicon vacancy center in diamond is among most promising sources for coherent single photons. Its large Debye–Waller factor, short lifetime and extraordinary spectral stability is unique in the field of solid-state single photon sources. However, the excitation and detection of individual centers requires high numerical aperture (NA) optics which, combined with the need for cryogenic temperatures, puts technical overhead on experimental realizations. Here, we investigate a hybrid quantum photonics platform based on silicon-vacancy center in nanodiamonds and metallic bullseye antenna to realize a coherent single-photon resource that operates efficiently down to low NA optics with an inherent resistance to misalignment.

Color centers in diamond are important quantum emitters for a broad range of applications ranging from quantum sensing to quantum optics. Understanding the internal energy level structure is of fundamental importance for future applications. We experimentally investigate the level structure of an ensemble of few negatively charged silicon-vacancy (SiV ^− ) and germanium-vacancy (GeV ^− ) centers in bulk diamond at room temperature by photoluminescence (PL) and excitation (PLE) spectroscopy over a broad wavelength range from 460 to $650\,\mathrm{nm}$ and perform power-dependent saturation measurements. For SiV ^− our experimental results confirm the presence of a higher energy transition at $\sim 2.31\,\mathrm{eV}$ . By comparison with detailed theoretical simulations of the imaginary dielectric function we interpret the transition as a dipole-allowed transition from ${}^{2}{E}_{g}$ -state to ${}^{2}{A}_{2u}$ -state where the corresponding a _2 _u -level lies deeply inside the diamond valence band. Therefore, the transition is broadened by the diamond band. At higher excitation power of $10\,\mathrm{mW}$ we indicate signs of a parity-conserving transition at $\sim 2.03\,\mathrm{eV}$ supported by saturation measurements. For GeV ^− we demonstrate that the PLE spectrum is in good agreement with the mirror image of the PL spectrum of the zero-phonon line. Experimentally we do not observe a higher lying energy level up to a transition wavelength of $460\,\mathrm{nm}$ . The observed PL spectra are identical, independent of excitation wavelength, suggesting a rapid decay to ${}^{2}{E}_{u}$ excited state and followed by optical transition to ${}^{2}{E}_{g}$ ground state. Our investigations convey important insights for future quantum optics and quantum sensing experiments based on SiV ^− -center and GeV ^− -center in diamond.

The recently demonstrated electroluminescence of color centers in diamond makes them one of the best candidates for room temperature single-photon sources. However, the reported emission rates are far off what can be achieved by state-of-the-art electrically driven epitaxial quantum dots. Since the electroluminescence mechanism has not yet been elucidated, it is not clear to what extent the emission rate can be increased. Here we develop a theoretical framework to study single-photon emission from color centers in diamond under electrical pumping. The proposed model comprises electron and hole trapping and releasing, transitions between the ground and excited states of the color center as well as structural transformations of the center due to carrier trapping. It provides the possibility to predict both the photon emission rate and the wavelength of emitted photons. Self-consistent numerical simulations of the single-photon emitting diode based on the proposed model show that the photon emission rate can be as high as 100 kcounts s ^−1 at standard conditions. In contrast to most optoelectronic devices, the emission rate steadily increases with the device temperature achieving of more than 100 Mcount s ^−1 at 500 K, which is highly advantageous for practical applications. These results demonstrate the potential of color centers in diamond as electrically driven non-classical light emitters and provide a foundation for the design and development of single-photon sources for optical quantum computation and quantum communication networks operating at room and higher temperatures.

The simultaneous imaging of magnetic fields and temperature (MT) is important in a range of applications, including studies of carrier transport and semiconductor device characterization. Techniques exist for separately measuring temperature (e.g., infrared (IR) microscopy, micro-Raman spectroscopy, and thermo-reflectance microscopy) and magnetic fields (e.g., scanning probe magnetic force microscopy and superconducting quantum interference devices). However, these techniques cannot measure magnetic fields and temperature simultaneously. Here, we use the exceptional temperature and magnetic field sensitivity of nitrogen vacancy (NV) spins in conformally coated nanodiamonds to realize simultaneous wide-field MT imaging at the device level. Our "quantum conformally attached thermo-magnetic" (Q-CAT) imaging enables (i) wide-field, high-frame rate imaging (100-1000 Hz); (ii) high sensitivity; and (iii) compatibility with standard microscopes. We apply this technique to study the industrially important problem of characterizing multifinger gallium nitride high-electron mobility transistors (GaN HEMTs). We spatially and temporally resolve the electric current distribution and resulting temperature rise, elucidating functional device behavior at the microscopic level. The general applicability of Q-CAT imaging serves as an important tool for understanding complex MT phenomena in material science, device physics, and related fields.

Integrated nanophotonics is an emerging field with high potential for quantum technology applications such as quantum sensing or quantum networks. A desired photonics platform is Si 3 N 4 due to low-photon loss and well-established fabrication techniques. However, quantum optics applications are not yet established. Here, we investigate an approach toward Si 3 N 4 -based quantum photonics utilizing a crossed waveguide, pump-probe design. The platform enables efficient, on-chip excitation, strong background suppression, and at the same time, efficient coupling to the mode of a high- Q photonic crystal cavity. The freestanding photonic crystal cavities reach high Q-factors up to 47 × 10 3 . To test our platform, we positioned an ensemble of negatively charged nitrogen vacancy centers located in a nanodiamond within the interaction zone of the photonic crystal cavity. We quantify the efficiency of the coupling with the β λ -factor reaching values as large as 0.71. We further demonstrate on-chip excitation of the quantum emitter with strong suppression (∼20 dB) of the background fluorescence. Our results unfold the potential to utilize negatively charged nitrogen vacancy centers in nanodiamonds and Si 3 N 4 platforms as an efficient, on-chip spin-photon interface in quantum photonics experiments.