Abstract Transverse-magnetic-field-induced spin mixing in nitrogen-vacancy (NV) centers hybridizes the |0⟩ and | ± 1⟩ manifolds, degrading optical spin polarization and spin-dependent fluorescence and thereby limiting optically detected magnetic resonance (ODMR) contrast and quantum-sensor fidelity. While recent work has clarified key elements of NV photophysics, how spin mixing evolves with temperature under device-relevant operating conditions─and how it intertwines with charge-state dynamics─remains insufficiently quantified. Here we perform systematic magnetic-field-temperature (B-T) mapping of transverse-field-induced photoluminescence (PL) quenching in an ensemble of NV centers. By spectrally resolving the NV– and NV0 zero-phonon-line emission, we disentangle spin-mixing-driven contrast loss within NV– from correlated changes in charge-state-resolved fluorescence. We introduce an operational critical field Bc extracted from the PL-contrast line shape, which provides a compact, reproducible figure-of-merit for transverse-field robustness and enables straightforward comparison across temperatures and field geometries. The measured temperature dependence of Bc is captured by a concise model incorporating phonon-mediated excited-state orbital dynamics, establishing a predictive framework for optimizing operating conditions and benchmarking ensemble NV sensing platforms.
Abstract Transverse-magnetic-field-induced spin mixing in nitrogen-vacancy (NV) centers hybridizes the |0⟩ and | ± 1⟩ manifolds, degrading optical spin polarization and spin-dependent fluorescence and thereby limiting optically detected magnetic resonance (ODMR) contrast and quantum-sensor fidelity. While recent work has clarified key elements of NV photophysics, how spin mixing evolves with temperature under device-relevant operating conditions─and how it intertwines with charge-state dynamics─remains insufficiently quantified. Here we perform systematic magnetic-field-temperature (B-T) mapping of transverse-field-induced photoluminescence (PL) quenching in an ensemble of NV centers. By spectrally resolving the NV– and NV0 zero-phonon-line emission, we disentangle spin-mixing-driven contrast loss within NV– from correlated changes in charge-state-resolved fluorescence. We introduce an operational critical field Bc extracted from the PL-contrast line shape, which provides a compact, reproducible figure-of-merit for transverse-field robustness and enables straightforward comparison across temperatures and field geometries. The measured temperature dependence of Bc is captured by a concise model incorporating phonon-mediated excited-state orbital dynamics, establishing a predictive framework for optimizing operating conditions and benchmarking ensemble NV sensing platforms.
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.
Point defects in diamond, also known as color centers, offer unique possibilities for solid-state quantum magnetometry. Here, we demonstrate and explore quantum spin mixing and optical readout of nitrogen vacancy diamond quantum states with a portable, educational toolkit from Quantum Education Initiative. Visible light photons electronically excite NV centers, upon which their integrated photoluminescence is measured through a free-space photodetector. With household magnets, changes in photoluminescence are correlated with changes in the NV electrons magnetic spin state to intuitively understand optical initialization and readout of an NV ensemble. As a continuous wave laser is used for excitation, we do not demonstrate the trivial procedure for optical readout for quantum gates. Rather, we employ a magnet with a non-zero transverse field component to induce steady-state spin mixing, allowing us to observe decreases in photoluminescence due to occupation of the m s =±1 sublevels.
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.
Modern sensing applications increasingly require the simultaneous measurement of multiple physical parameters with high sensitivity. However, traditional sensors often suffer from cross-sensitivity to different variables, making it difficult to separate overlapping effects, such as those caused by temperature and magnetic fields, in complex environments. This challenge highlights the need for robust multiparametric sensors capable of independently and accurately monitoring diverse conditions in real time. In this context, nitrogen-vacancy (NV) centers in diamond present a promising solution. These atomic-scale defects can be optically initialized, manipulated, and read out via laser excitation using optically detected magnetic resonance (ODMR), and they can operate under ambient and harsh conditions. In this work, we demonstrate a simultaneous and internally cross-validated sensing platform capable of detecting both magnetic fields and temperature with a sensitivity of around 500 nT/Hz and 10 mK/Hz, respectively. Our method integrates ODMR, zero-phonon line spectral shifts, and linewidth broadening, each providing independent spectral signatures sensitive to distinct physical effects. This approach enhances measurement precision, enables internal consistency checks, and decouples intertwined phenomena such as temperature-induced variations in magnetization. The demonstrated technique significantly expands the functional capabilities of NV-based sensors, advancing their potential for high-precision metrology in complex environments.
We investigate the magnetic field dependent photophysics of individual nitrogen-vacancy (NV) color centers in diamond under cryogenic conditions. At distinct magnetic fields, we observe significant reductions in the NV photoluminescence rate, which indicate a marked decrease in the optical readout efficiency of the NV's ground state spin. We assign these dips to excited state level anticrossings, which occur at magnetic fields that strongly depend on the effective, local strain environment of the NV center. Our results offer new insights into the structure of the NVs' excited states and a new tool for their effective characterization. Using this tool, we observe strong indications for strain-dependent variations of the NV's orbital g factor, obtain new insights into NV charge state dynamics, and draw important conclusions regarding the applicability of NV centers for low-temperature quantum sensing.
The spin dynamics of the negatively charged nitrogen-vacancy (NV⁻) centers in diamond are highly sensitive to quantum electromagnetic fluctuations arising from optical excitation, chemical interactions, and thermal processes. Here we investigated the optical and spin properties of ensembles of NV⁻ centers in diamond under continuous-wave (CW) and nanosecond pulsed laser excitation. Optical detection of magnetic resonance (ODMR) is employed to monitor laser induced shifts of the zero-field splitting parameter D under ambient and high-vacuum conditions. Increasing CW laser power results in a systematic downshift of the resonance frequency due to laser-induced heating. The effect is significantly enhanced under vacuum, where the shift in D reaches up to ~17 MHz, compared to ~5 MHz in air, emphasizing the role of environmental thermal dissipation. Under nanosecond pulsed excitation, increasing the pulse repetition rate similarly leads to resonance shifts and reduced ODMR contrast, consistent with cumulative thermal effects. Visible and infrared spectroscopy confirm power dependent modifications of NV emission. Time resolved photoluminescence measurements showed that the excited-state lifetime (~6 ns) remains nearly constant across the investigated excitation range, indicating that in this regime the dominant limitation is thermal loading of the spin resonance rather than a change in intrinsic radiative decay dynamics. These results provide a comprehensive characterization of thermal effects in high power optical excitation of NV ensembles and are directly relevant for high intensity NV-based sensing and spectroscopy, particularly in vacuum environments.