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IEEE Photonics Conference

Studying the Single and Ensemble of NV Center Emission for Enhanced Magnetic Field Sensitivity

Ashish Redhu, Rajesh V. Nair

Published Nov 9, 2025• 0 citations
Publisher

Abstract

We investigate high-density ensembles of nitrogen-vacancy (NV) centers in diamond for quantum sensing. Stable NV-charge states are observed under high-power excitation. Enhanced photon emission yields over fivefold sensitivity improvement compared to single NVs, demonstrating the potential of ensembles for high-performance sensing applications.

DOI
10.1109/ipc65510.2025.11282423

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We investigate high-density ensembles of nitrogen-vacancy (NV) centers in diamond for quantum sensing. Stable NV-charge states are observed under high-power excitation. Enhanced photon emission yields over fivefold sensitivity improvement compared to single NVs, demonstrating the potential of ensembles for high-performance sensing applications.
Among quantum sensors, the single nitrogen-vacancy (NV) defect in diamond has the highest sensitivity-to-size factor. For instance, a single-NV spin when used as a magnetometer could achieve sensitivities of the order of nT/Hz, while the dimensions of the sensor are merely atomic in size. The sensitivity is limited only by the photon shot noise. One method to boost the magnetometer sensitivity to pico-tesla scales is to use many NV defect centers as an ensemble sensor [Phys. Rev. X5, 041001 (2015)PRXHAE2160-330810.1103/PhysRevX.5.041001]. However, during the absorption-emission (fluorescence) optical cycles, the NV centers transfer a portion of the irradiation laser energy into phonons and heat the diamond matrix. This results in unintended fluorescence decrease, spin resonance lines shifts, and fluctuations. Hence, the advantages gained by packing a high density of NV centers are significantly reduced. Here we investigate the heat generation of ensemble NV centers in micrometer-sized diamond under 532 nm laser irradiation and its effects pertaining to sensing applications. These investigations help us to find strategies that mitigate the detrimental effects of heating and yet permits the use of ensemble NV defects for improved metrology applications.
Negatively charged nitrogen-vacancy (NV) centers in diamond are promising magnetic field quantum sensors. Laser threshold magnetometry theory predicts improved NV center ensemble sensitivity via increased signal strength and magnetic field contrast. Here, we experimentally demonstrate laser threshold magnetometry. We use a macroscopic high-finesse laser cavity containing a highly NV-doped and low absorbing diamond gain medium that is pumped at 532 nm and resonantly seeded at 710 nm. This enables a 64% signal power amplification by stimulated emission. We test the magnetic field dependency of the amplification and thus demonstrate magnetic field-dependent stimulated emission from an NV center ensemble. This emission shows an ultrahigh contrast of 33% and a maximum output power in the milliwatt regime. The coherent readout of NV centers pave the way for novel cavity and laser applications of quantum defects and diamond NV magnetic field sensors with substantially improved sensitivity for the health, research, and mining sectors.
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.
Nitrogen Vacancy (NV) centers are point defects in diamond that allow magnetic field sensing based on Optically Detected Magnetic Resonance (ODMR). They are processed in ultrapure single-domain CVD grown diamond crystals and can be operated at room temperature. This results in solid-state sensors with a wide variety of applications. Ensemble of NV centers can be used to perform wide-field magnetic imaging with sensitivity in the nT range. Single NV centers can also be processed, which allows sensing at the atomic scale. This possibility, combined with its unique coherence properties, make NV center an ideal candidate for quantum sensing.
Advances in sensing devices that utilize nitrogen-vacancy (NV) center ensembles in diamond are driving progress in microscale nuclear magnetic resonance spectroscopy. Utilizing quantum sensing techniques in the high-field regime significantly boosts sensitivity by increasing thermal polarization and improves spectral quality via enhanced energy shifts. Compatible with the latter, a straightforward manner to further raise sensor sensitivity is to increase NV concentration, although this intensifies detrimental dipole-dipole interactions among NVs. In this Letter, we present a method for detecting NMR signals in high-field scenarios while effectively suppressing dipole-dipole couplings in the NV ensemble. Thus, this approach enhances sensitivity by combining highly doped diamond substrates and elevated magnetic fields.
Nitrogen-Vacancy (NV) centers in diamond have emerged as a leading platform for quantum sensing, particularly in magnetic field detection. Efficient interrogation of large NV ensembles is crucial for achieving high sensitivity. This paper presents a comprehensive analysis of the optical efficiencies that govern the performance of NV-based sensing systems, focusing on excitation, conversion, and collection, leading to a novel collection design improving upon state-of-the-art results. To optimize various excitation schemes, we developed numerical tools capable of accurately calculating excitation efficiencies for arbitrary power density distributions. Using these tools, we investigated several techniques, including reflective coatings and corner excitation, and achieved excitation efficiencies exceeding 0.7, compared to the∼0.4\sim 0.4∼0.4efficiency achieved by standard methods. We also measured the conversion efficiency of NV centers, quantifying the ratio of absorbed green excitation vs. fluorescence, in various diamond samples. This value is usually missing in the literature, and therefore important to quantify in different regimes. We obtained a value of ηv=0.22 ± 0.03, which is consistent with theoretical expectations. Furthermore, we designed and experimentally validated a novel Compound Trapezoid Collector (CTC) for enhanced photon collection. The CTC offers performance comparable to that of traditional Compound Parabolic Collectors (CPCs), but with a significantly smaller form factor and simplified manufacturing. Our prototype CTC achieved a collection efficiency of 0.33, with the potential to reach approximately∼0.8\sim 0.8∼0.8. This work provides insights into optimizing the optical efficiencies of NV-based sensing systems and contributes to the development of practical devices.