The negatively charged nitrogen-vacancy (N-V(-)) color center in diamond is an important solid-state single photon source for applications to quantum communication and distributed quantum computation. Its full usefulness relies on sufficient radiative emission of the optical photons which requires realizable control to enhance emission into the zero-phonon line (ZPL) but until now is still a challenge. Detailed understanding of the associated excitation process would be of essential importance for such objective. Here we report a theoretical work that probes the spin-conserving optical excitation of the N-V(-) center. Using density-functional-theory (DFT) calculations, we find that the ZPL and the phonon-side band (PSB) depend sensitively on the axial strain of the system. Besides, we find a relatively small PSB appearing at about 100 GPa in the emission spectrum at low temperatures, which provides a means to enhance the coherent emission of the N-V(-) center in quantum optical networks.
The negatively charged nitrogen-vacancy (N-V(-)) color center in diamond is an important solid-state single photon source for applications to quantum communication and distributed quantum computation. Its full usefulness relies on sufficient radiative emission of the optical photons which requires realizable control to enhance emission into the zero-phonon line (ZPL) but until now is still a challenge. Detailed understanding of the associated excitation process would be of essential importance for such objective. Here we report a theoretical work that probes the spin-conserving optical excitation of the N-V(-) center. Using density-functional-theory (DFT) calculations, we find that the ZPL and the phonon-side band (PSB) depend sensitively on the axial strain of the system. Besides, we find a relatively small PSB appearing at about 100 GPa in the emission spectrum at low temperatures, which provides a means to enhance the coherent emission of the N-V(-) center in quantum optical networks.
The realisation of an efficient spin-photon interface using the negatively charged nitrogen-vacancy centre (NV-) in diamond requires the resonant coupling of the zero phonon line (ZPL) of the centre to an optical microcavity [1]. The cavity serves to encourage emission into the ZPL in preference to the phonon sidebands, and potentially also to increase the homogeneous linewidth via a reduction of the lifetime (the Purcell effect) thus assisting in the generation of indistinguishable photons. Cavity coupling thus has potential to improve by orders of magnitude the speed with which entanglement can be created between spatially remote NV- centres [2], and to enable other mechanisms for realising spin-photon interfaces via non-demolition measurements [3].
A quantum-chemical study of the positive charge-state of the nitrogen-vacancy center in diamond is presented. Charge control of this promising qubit candidate is a focus of diamond quantum technology research, as currently charge stability relating to surfaces and nearby defects causes some difficulties for quantum applications. To demonstrate full charge control over the nitrogen vacancy, all three charge states should be identified and the processes that lead to charge state changes understood. However, experimental markers for the positive state remain elusive compared to the readily detectable zero-phonon lines of the neutral and negative. In this work we present predicted hyperfine and zero-field splitting tensors as clear signatures of the normally spinless NV+(1A1 ground state) by probing a long-lived spin-triplet excited-state $\ensuremath{\sim}0.7$ eV above the NV+ ground state. We find a relatively narrow excitation energy range of approximately 0.7--1.1 eV between excitation into an 3E state and conversion into the neutral charge state. To provide insight into the thermal stability of the positive charge state, we have calculated binding and diffusion energies for both charged and uncharged systems. We predict, given that the activation energies are only weakly charge state dependent, all three charge states would diffuse in the 1600--$1900{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\text{C}$ range, but the positive state has a significantly lower binding energy, suggesting that it will dissociate at temperatures around $1000{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ rather than migrate.
Color centers in diamond are a promising platform for quantum communication, as they can serve as solid state quantum memories with efficient optical transitions. Much recent attention has focused on the negatively charged NV center in diamond, which has a spin triplet ground state electronic configuration that can be measured and initialized optically, exhibits long spin coherence times at room temperature, and has narrow, spin-conserving optical transitions. However, the NV center exhibits a large static and dynamic inhomogeneous linewidth, and over 97% of its emission is in a broad, incoherent phonon side band, severely limiting scalability. Alternatively, the negatively charged SiV center exhibits excellent optical properties, with 70% of its emission in the zero phonon line and a narrow inhomogeneous linewidth. However, SiV− suffers from short electron spin coherence times, limited by an orbital relaxation rate (T1) of around 40 ns at 5 K.
We report on the spectroscopic and laser characterization of negatively charged nitrogen-vacancy (NV−) centers in diamond. Spectroscopic properties such as absorption and emission spectra as well as kinetics were studied, and parameters such as cross-sections and lifetimes were estimated. A vibronic band of NV0 with zero phonon line (ZPL) at 575 nm was detected under 532 nm pulsed excitation due to the photoionization of NV−. Transmission of 532 nm pump pulses saturate around ∼10%, which is much smaller than the theoretical level. Δk/k0 kinetics revealed slow recovery of NV− centers after photoionization under 532 nm pumping, which involved different relaxation channels depending on the probe beam wavelengths. Localization of the electrons in the metastable state of NV0 centers resulted in higher saturated transmission of 632 nm pump.
Nitrogen-vacancy (NV) centers in single-crystal CVD diamond are promising candidates for quantum sensing due to their remarkable optical and spin properties [1]. These defects exhibit stable photoluminescence (PL), long spin coherence times, and high sensitivity to external fields [2]. In this study, we present a room-temperature PL characterization of NV centers excited with a 532 nm laser. The setup was optimized for high signal-to-noise ratio and spectral resolution. Key parameters analyzed include emission intensity, zero-phonon line (ZPL) at ~637 nm, phonon sidebands, and the charge state distribution between NV⁰ and NV⁻. The NV⁻ state, crucial for spin-based sensing, is evaluated to understand its stability under different nitrogen doping conditions [3]. The relative intensities of NV⁰ and NV⁻ provide insights into nitrogen incorporation and vacancy formation. These results contribute to optimizing synthesis conditions for enhanced NV⁻ concentration, supporting the advancement of diamond-based quantum sensing technologies.
The nitrogen-vacancy (NV) center in diamond enables optical initialization and readout of its electronic spin, forming the basis of a wide range of quantum sensing and metrology applications. A central challenge in such measurements is the coexistence of two charge states, NV- and NV0: While detection protocols rely on the spin-dependent properties of NV-, fluorescence from NV0 does not carry useful contrast and is typically removed as background, reducing the available signal. Here, we show that the origin of NV0 emission depends strongly on the excitation wavelength in nitrogen-containing diamond. Using ensembles of NV centers with varying nitrogen concentrations, we compare excitation at the NV0 zero-phonon line (ZPL) at 575 nm with the commonly used 532 nm. We find that excitation at 575 nm generates NV0 predominantly through spin-selective tunneling from the excited state of NV- to nearby nitrogen donors, such that the NV0 emission follows the spin polarization of NV-. As a result, the NV0 fluorescence contributes to the measurable spin contrast, allowing the full fluorescence signal to be used for detection. This result opens opportunities for improved sensitivity in NV-based sensing applications.