We demonstrate the use of two-photon excitation for observing the ground state optically detected magnetic resonance (ODMR) of nitrogen-vacancy centers in diamonds at room temperature. An ultrafast femtosecond laser at 1040 nm was used for excitation, while fluorescence signal read out was achieved through a combination of a PMT and a lock-in amplifier. The imaging capability of two-photon excitation fluorescence (2PEF) was utilized to map the distribution of NV centers in a bulk diamond and micro-sized diamonds. For the first time, ODMR traces of the nitrogen-vacancy center are observed with two-photon excitation, providing a promising tool for fast 3D quantum sensing and imaging.
We demonstrate the use of two-photon excitation for observing the ground state optically detected magnetic resonance (ODMR) of nitrogen-vacancy centers in diamonds at room temperature. An ultrafast femtosecond laser at 1040 nm was used for excitation, while fluorescence signal read out was achieved through a combination of a PMT and a lock-in amplifier. The imaging capability of two-photon excitation fluorescence (2PEF) was utilized to map the distribution of NV centers in a bulk diamond and micro-sized diamonds. For the first time, ODMR traces of the nitrogen-vacancy center are observed with two-photon excitation, providing a promising tool for fast 3D quantum sensing and imaging.
We demonstrate the use of two-photon excitation for observing the ground-state optically detected magnetic resonance (ODMR) of nitrogen-vacancy centers in diamonds at room temperature. An ultrafast femtosecond laser at 1040 nm was used for excitation, while fluorescence signal readout was achieved through a combination of a PMT and a lock-in amplifier. The imaging capability of two-photon excitation fluorescence (2PEF) was utilized to map the relative distribution of NV centers in a bulk diamond and micro-sized diamonds. For the first time, to the best of our knowledge, ODMR traces of the nitrogen-vacancy center are observed with two-photon excitation, providing a promising tool for fast 3D quantum sensing and imaging.
The color centers in diamonds are promising candidates in the context of quantum information science, quantum computation, and spin-based quantum sensors due to their exceptional spin-dependent emission properties. The manipulation and the optical readout of the spin state is measured using a spectroscopic technique known as the Optically Detected Magnetic Resonance (ODMR). Here, we discuss the indigenous development of an ODMR setup to manipulate and measure the spin state of nitrogen-vacancy centers in diamond. The study involves the confocal mapping of NV centers to measure the spin state by applying a micro-wave field. The spin state control appears as a dip in the measured emission intensity as a function of micro-wave frequency.
As promising quantum sensors, nitrogen-vacancy (N-V) centers in diamond have been widely used in frontier studies in condensed-matter physics, material science, and life sciences. In practical applications, weak laser excitation is favorable as it reduces the side effects of laser irradiation, such as phototoxicity and heating. Here we report a combined theoretical and experimental study of (near) zero-field optically detected magnetic resonance (ODMR) of N-V-center ensembles under weak 532-nm laser excitation. In this region, both the width and splitting of the ODMR spectra decrease with increasing laser power. This power dependence is reproduced with a model that accounts for the laser-induced charge neutralization of $\mathrm{N}\text{\ensuremath{-}}{V}^{\ensuremath{-}}$--N+ pairs, which alters the local electric field environment. These results are useful for the understanding and development of N-V-based quantum sensing in light-sensitive applications.
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.
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.
Abstract Multiple-microwave-photon transition is a nonlinear process involving the simultaneous absorption of multiple microwave photons to reach a higher energy state. This phenomenon enables microwave frequency conversion, a crucial technique for spin-wave devices, frequency synthesizers and communication devices. However, it has not been observed in nitrogen-vacancy (NV) centers in diamonds, which serve as a key quantum platform linking flying qubits, microwave photons, and solid-state spins. In this work, we first observed multiple-microwave-photon transitions in NV centers in diamonds, using optically detected magnetic resonance (ODMR) methods with a single laser and microwave beam. We demonstrate that microwave frequencies, effective g-factor, and angular momentum exhibit a 1/n scaling law, but the linewidth exhibits a 1/n^2 scaling law for n-photon transitions between the ground states. Additionally, we detect the hyperfine structure of the ground states and achieve coherent spin manipulation under multi-photon excitation. Our findings offer a novel approach for the precise manipulation of NV center spin states, advancing quantum sensing and quantum information.