We present a dual-wavelength analysis of nitrogen-vacancy (NV) center quantum magnetometry enhanced by uniformly coated gold nanoparticles (AuNPs). An ensemble-averaged model is developed to analyze the AuNP-enhanced stimulated absorption at the 532 nm excitation wavelength and the spontaneous emission at 637 nm. The resulting detected optically magnetic resonance (ODMR) signal profiles are simulated for both enhancement mechanisms. We find that the enhanced stimulated absorption at 532 nm significantly amplifies the ODMR signal intensity without broadening the linewidth, thereby improving the signal-to-noise ratio (SNR) without sacrificing the magnetic field sensing resolution. Conversely, enhancing the 637 nm spontaneous emission increases the total photo emission rate but simultaneously broadens the ODMR detection linewidth due to the direct reduction in the effective spin coherence time of excited states by the enhanced spontaneous rate. The dual-wavelength analysis provides valuable design guidance for the development of low-cost spin-coated AuNP-enhanced NV-center quantum magnetometry technologies.
We present a dual-wavelength analysis of nitrogen-vacancy (NV) center quantum magnetometry enhanced by uniformly coated gold nanoparticles (AuNPs). An ensemble-averaged model is developed to analyze the AuNP-enhanced stimulated absorption at the 532 nm excitation wavelength and the spontaneous emission at 637 nm. The resulting detected optically magnetic resonance (ODMR) signal profiles are simulated for both enhancement mechanisms. We find that the enhanced stimulated absorption at 532 nm significantly amplifies the ODMR signal intensity without broadening the linewidth, thereby improving the signal-to-noise ratio (SNR) without sacrificing the magnetic field sensing resolution. Conversely, enhancing the 637 nm spontaneous emission increases the total photo emission rate but simultaneously broadens the ODMR detection linewidth due to the direct reduction in the effective spin coherence time of excited states by the enhanced spontaneous rate. The dual-wavelength analysis provides valuable design guidance for the development of low-cost spin-coated AuNP-enhanced NV-center quantum magnetometry technologies.
A method for enhancement of the sensitivity of a spin sensor based on an ensemble of nitrogen vacancy (NV) color centers was demonstrated. Gold nanoparticles (NPs) were deposited on the bulk diamond, which had NV centers distributed on its surface. The experimental results demonstrate that, when using this simple method, plasmon enhancement of the deposited gold NPs produces an improvement of ∼10 times in the quantum efficiency and has also improved the signal-to-noise ratio by approximately ∼2.5 times. It was also shown that more electrons participated in the spin sensing process, leading to an improvement in the sensitivity of approximately seven times; this has been proved by Rabi oscillation and optical detection of magnetic resonance (ODMR) measurements. The proposed method has proved to be a more efficient way to design an ensemble of NV centers-based sensors; because the result increases in the number of NV centers, the quantum efficiency and the contrast ratio could greatly increase the device's sensitivity.
Magnetometry with nitrogen-vacancy (NV) centers in diamond has so far been measured via emission of light from NV centers or via absorption at the singlet transition at 1042 nm. Here, we demonstrate a phenomenon of broadband optical absorption by the NV centers starting in the emission wavelength and reaching up to 1000 nm. The measurements are enabled by a high-finesse cavity, which is used for room-temperature continuous wave pump-probe experiments. The red to infrared probe beam shows the typical optically detected magnetic resonance (ODMR) signal of the NV spin with contrasts up to 42 %. This broadband optical absorption has not yet been reported in terms of NV magnetometry. We argue that the lower level of the absorbing transition could be the energetically lower NV singlet state, based on the increased optical absorption for a resonant microwave field and the spectral behavior. Investigations of the photon-shot-noise-limited sensitivity show improvements with increasing probe wavelength, reaching an optimum of 7.5pT/Hz. The results show significantly improved ODMR contrast compared to emission-based magnetometry. This opens a new detection wavelength regime with coherent laser signal detection for high-sensitivity NV magnetometry.
Nitrogen-vacancy (NV) centers in diamond are a leading platform for solid-state quantum sensing and quantum information processing. While most optical studies rely on the visible fluorescence associated with the triplet transitions, the infrared singlet transition near 1042 nm, which is typically considered dark within the singlet manifold of the NV optical cycle, provides an alternative optical channel. Here, we report wavelength-resolved optically detected magnetic resonance (ODMR) measurements of this infrared emission. We directly observe ODMR contrast in the 1042 nm emission and analyze its dependence on the magnetic field. The field-dependent spectral dispersion of the ODMR signal demonstrates that the spin-state information encoded in the NV center is transcribed to the infrared singlet emission through the spin-selective intersystem crossing, in close analogy to the visible fluorescence readout. These results establish infrared ODMR as a high-fidelity optical readout pathway. Crucially, by extending spin-state transcription directly into the 1300−1600 nm range, this work demonstrates a direct, conversion-free interface between diamond spin-qubits and standard telecommunication infrastructure, bypassing the efficiency bottlenecks of active frequency conversion and benefiting from the already well-developed technologies in this range of the electromagnetic spectrum.
Magnetometry with nitrogen-vacancy (NV) centers in diamond has shown great promise in recent years. In particular, absorption-based magnetometry techniques, employing a cavity to enhance the absorption length, can improve the contrast and sensitivity compared to conventional techniques based on reading out the NV− triplet fluorescence. The absorption techniques rely on magnetic-field-dependent absorption at the NV− singlet zero phonon line at 1042nm and its phonon sideband. In a cavity-enhanced spectroscopy approach, we study pump-laser- and microwave-induced cavity signal changes at room temperature over a spectral range of 680-1050nm. Through normalization, we eliminate the cavity-enhancement effect and provide quasi-single-pass values for the absorption and optically detected magnetic resonance (ODMR) contrast. The highest contrast is found at 1042nm, but multiple points of high contrast are found at the peaks of the phonon sideband. Additionally, cavity-enhanced ODMR contrasts in the range of 50-80% are presented. We further measure the broadband singlet absorption cross section at room temperature with a novel method through microwave-induced signal changes. This method is insensitive to pump-laser-induced signal changes by other defects and quantifies the room-temperature absorption strength of the singlet transition and its entire phonon sideband. We determine the absorption cross section at 1042nm to be σ1042★=(0.89±0.14)⋅10−21m2 or σ1042▲=(2.9±0.5)⋅10−21m2. depending on the employed 532nm NV− absorption cross section.
Magnetometry by using NV center, a localized coherent spin consisting of a pair of nitrogen atom and atomic void, in diamond is now regarded as a promising technique due to its potential for high sensitivity and miniaturization. The primary application for NV magnetometry was realized by optically detected magnetic resonance (ODMR). There have been plenty of reports on demonstration of magnetic sensing by using ODMR1. Towards simpler and more reliable implementation of NV magnetometry, photocurrent-detected magnetic resonance2 (PDMR) is one of the key technologies to bypass the bulky confocal optics that are necessary for ODMR-based photoluminescence detection. In a PDMR scheme, meanwhile, we use photocurrent to read out the NV spin state, which necessitates laser irradiation only for photoexcitation and spin initialization. The key for high sensitivity of PDMR-based magnetometry3 is low noise to spin-dependent signal ratio. For this sake, it is essential to mitigate the unwanted spin-independent photocurrent while maximizing the PDMR signal. In this study, we employed two different laser power and time4 in the pulse sequence to improve the signal to noise ratio5. As a result, the magnetic sensitivity as high as 13 nT/Hz0.5 was achieved.
Quantum sensing using nitrogen-vacancy (NV) centers in diamond has emerged as a powerful platform for detecting ultra-low magnetic fields under ambient conditions. Owing to their long spin coherence times, optical addressability, and compatibility with aqueous environments, it has found widespread applications in biosensing and bio-imaging. This review presents the fundamental principles and recent advances in NV-based quantum magnetometry for biosensing applications, with a particular focus on measurements in aqueous medium and at cellular and molecular length scales. We discuss the underlying spin physics of NV centers and highlight two primary detection modalities: optically detected magnetic resonance (ODMR) and T1 relaxometry-based sensing and how these approaches aids in the detection of both static magnetic fields and dynamic magnetic noise arising from biological processes. The review explores key application areas, including nanoscale nuclear magnetic resonance (NMR), monitoring of neural activity, detection of abnormal or rogue cells using NV-based platforms etc. In addition, strategies for enhancing sensitivity, such as surface functionalization of nanodiamonds, femtosecond (fs) laser-written photonic structures, and integration with microfluidic and lab-on-chip systems have also been discussed in depth. We also address the critical challenges, including surface-induced decoherence, charge-state instability, and signal-to-noise limitations in biofluids associated with NV-based biosensing applications. Finally, we outline future prospects, highlighting how NV-based magnetic biosensing provides a promising pathway for translating quantum sensing technologies into practical biomedical applications.