Nitrogen-vacancy centres (NVs) are promising solid-state nanoscale quantum sensors for applications ranging from material science to biotechnology. Using multiple sensors simultaneously offers advantages for probing spatiotemporal correlations of fluctuating fields or the dynamics of point defects. In this work, by integrating NVs with foundry silicon-nitride photonic integrated circuits, we realise the scalable operation of eight localised NV sensors in an array, with simultaneous, distinct readout of the individual sensors. Using the eight NV sensors and machine-learning methods for multi-point magnetic field reconstruction, we demonstrate microscale magnetic localisation of a 30 $μ$m-sized needle tip. Experimentally, the needle tip can be localised with an error below its dimension and tracked dynamically with high fidelity. We further simulate the feasibility of our platform for monitoring the position and orientation of magnetic microrobots designed for biological and clinical purposes. Without the complexity of bulk optics, our photonic-integrated multi-sensor platform presents a step towards real-life biomedical applications under out-of-the-lab conditions.
Nitrogen-vacancy centres (NVs) are promising solid-state nanoscale quantum sensors for applications ranging from material science to biotechnology. Using multiple sensors simultaneously offers advantages for probing spatiotemporal correlations of fluctuating fields or the dynamics of point defects. In this work, by integrating NVs with foundry silicon-nitride photonic integrated circuits, we realise the scalable operation of eight localised NV sensors in an array, with simultaneous, distinct readout of the individual sensors. Using the eight NV sensors and machine-learning methods for multi-point magnetic field reconstruction, we demonstrate microscale magnetic localisation of a 30 μm-sized needle tip. Experimentally, the needle tip can be localised with an error below its dimension and tracked dynamically with high fidelity. We further simulate the feasibility of our platform for monitoring the position and orientation of magnetic microrobots designed for biological and clinical purposes. Without the complexity of bulk optics, our photonic-integrated multi-sensor platform presents a step towards real-life biomedical applications under out-of-the-lab conditions.
Nitrogen-vacancy (NV) centres are exceptional solid-state quantum sensors with optically addressable spins. With room-temperature operability and biocompatibility, functionalised NV centres in nanodiamonds facilitate atomic-scale tracking and real-time monitoring of physical and chemical properties within living systems [1]. Conventionally, these systems work by addressing stochastically-positioned defects with a complex bulk-optic microscope [2] or using a single scanning probe, limited in scalability and the ability to capture spatial and temporal information simultaneously.
Single nitrogen vacancy (NV) centers in diamond have been used extensively for high-sensitivity nanoscale sensing, but conventional approaches use confocal microscopy to measure individual centers sequentially, limiting throughput and access to nonlocal physical properties, where simultaneous, high-fidelity measurement of multiple centers is required. Here, we design and implement a multiplexed NV sensing platform that allows us to read out many single NV centers simultaneously using a low-noise camera. Using this platform, we coherently manipulate and read out the spin states of hundreds of individual NV centers in parallel, achieving comparable magnetic field sensitivity to confocal measurements. We also implement a parallelized version of spin-to-charge-conversion readout for low NV center spin state readout noise and use it to demonstrate multiplexed covariance magnetometry, in which we measure ten two-point magnetic field correlators from five NV centers simultaneously. From these measurements, we demonstrate the quantitative reconstruction of spatially varying magnetic correlations arising from a current-carrying wire. The number of correlators we can measure is limited only by the available laser power, opening the door to massively multiplexed covariance magnetometry. In contrast to scanning probes for imaging spatially varying magnetic fields, our approach measures the temporal dynamics of the magnetic field at many precisely defined positions simultaneously, from which the local noise spectrum and nonlocal properties such as correlation functions can be computed. This high-fidelity readout platform will find immediate applications in studying condensed matter phenomena that are characterized by the noise spectrum or correlation functions, including quantum phase transitions, dynamics far from equilibrium, magnetic order, and correlated electron phenomena.
Nitrogen-vacancy (NV) centres in diamond are promising quantum systems for sensing applications due to their quantum coherence, optical addressability, and robust performance even at room temperature [1], [2]. These properties allow for the precise measurement of environmental parameters, such as magnetic fields [2], electric fields, strain, and temperature [1]–[4]. This work focuses on a portable multisensing platform based on NV centres, examining its performance across a temperature range of -20°C to 120°C [2]. Understanding the temperature dependence of the spectral features of NV centres is crucial not only to assess its capabilities for multisensing, but also for optimising the device for diverse operating conditions and for ensuring the precision and reliability of quantum measurements [3]. While many studies focus on low temperatures or individual NV centres, this work focuses on an ensemble of NV centres at relatively high temperatures, which is more suitable for portable sensors [1], [5]. This work is novel as it provides a comprehensive study of a portable NV -based multisensor's performance at relatively high temperatures, crucial for real-world applications [1].
Nitrogen-vacancy (NV) centres in diamond show great promise for quantum computing, where photonic entanglement can be generated using long-lived optically-active spins [1]. A quantum processor would require a large number of interconnected NV centres, and an integrated platform becomes necessary for control and routing. Benefits of integration include nanophotonic cavities with ultra-small mode volumes [2], multilayer electronics, and use of existing integrated quantum photonic components and architectures. Pick-and-place methods have been adopted to combine diamond microchiplets with aluminium nitride [3]. Photonic and spin properties has also been measured in nanodiamond encapsulated in optimised silicon nitride (SiNx) [4]. However, challenges remain to interface diamond with photonics in a scalable and manufacturable process. In particular, the need to identify and manipulate stochastically located emitters requires precise and time-intensive confocal microscopy.
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.
In modern-day quantum metrology, quantum sensors are widely employed to detect weak magnetic fields or nanoscale signals. Quantum devices, exploiting quantum coherence, are inevitably connected to physical constants and can achieve accuracy, repeatability, and precision approaching fundamental limits. As a result, these sensors have shown utility in a wide range of research domains spanning both science and technology. A rapidly emerging quantum sensing platform employs atomic-scale defects in crystals. In particular, magnetometry using nitrogen-vacancy (NV) color centers in diamond has garnered increasing interest. NV systems possess a combination of remarkable properties, optical addressability, long coherence times, and biocompatibility. Sensors based on NV centers excel in spatial resolution and magnetic sensitivity. These diamond-based sensors promise comparable combination of high spatial resolution and magnetic sensitivity without cryogenic operation. The above properties of NV magnetometers promise increasingly integrated quantum measurement technology, as a result, they have been extensively developed with various protocols and find use in numerous applications spanning materials characterization, nuclear magnetic resonance (NMR), condensed matter physics, paleomagnetism, neuroscience and living systems biology, and industrial vector magnetometry. In this chapter, NV centers are explored for magnetic sensing in a number of contexts. In general, we introduce novel regimes for magnetic-field probes with NV ensembles. Specifically, NV centers are developed for sensitive magnetometers for applications where microwaves (MWs) are prohibitively invasive and operations need to be carried out under zero ambient magnetic field. The primary goal of our discussion is to improve the utility of these NV center-based magnetometers.