An integrated magnetometry platform with stackable waveguide-assisted detection channels for sensing arrays
Michael Hoese, M. Koch, Vibhav Bharadwaj, Johannes Lang, John Patrick Hadden, Reina Yoshizaki, Argyro N. Giakoumaki, Roberta Ramponi, Fedor Jelezko, Shane Michael Eaton, Alexander Kubanek
The negatively-charged NV−-center in diamond has shown great success in nanoscale, high-sensitivity magnetometry. Efficient fluorescence detection is crucial for improving the sensitivity. Furthermore, integrated devices enable practicable sensors. Here, we present a novel architecture which allows us to create NV−-centers a few nanometers below the diamond surface, and at the same time in the mode field maximum of femtosecond-laser-written type-II waveguides. We experimentally verify the coupling efficiency, showcase the detection of magnetic resonance signals through the waveguides and perform first proof-of-principle experiments in magnetic field and temperature sensing. The sensing task can be operated via the waveguide without direct light illumination through the sample, which marks an important step for magnetometry in biological systems which are fragile to light. In the future, our approach will enable the development of two-dimensional sensing arrays facilitating spatially and temporally correlated magnetometry.
The negatively-charged NV−-center in diamond has shown great success in nanoscale, high-sensitivity magnetometry. Efficient fluorescence detection is crucial for improving the sensitivity. Furthermore, integrated devices enable practicable sensors. Here, we present a novel architecture which allows us to create NV−-centers a few nanometers below the diamond surface, and at the same time in the mode field maximum of femtosecond-laser-written type-II waveguides. We experimentally verify the coupling efficiency, showcase the detection of magnetic resonance signals through the waveguides and perform first proof-of-principle experiments in magnetic field and temperature sensing. The sensing task can be operated via the waveguide without direct light illumination through the sample, which marks an important step for magnetometry in biological systems which are fragile to light. In the future, our approach will enable the development of two-dimensional sensing arrays facilitating spatially and temporally correlated magnetometry.
On-chip magnetic field sensing with nitrogen-vacancy (NV) centers in diamond requires scalable integration of 3D waveguides into diamond substrates. Here, we develop a sensing array device with an ensemble of shallow implanted NV centers integrated with arrays of laser-written waveguides for excitation and readout of NV signals. Our approach enables an easy-to-operate on-chip magnetometer with a pixel size proportional to the Gaussian mode area of each waveguide. The performed continuous wave optically detected magnetic resonance on each waveguide gives an average dc-sensitivity value of (195±3) nT/Hz, which can be improved with lock-in-detection or pulsed-microwave sequences. We apply a magnetic field to separate the four NV crystallographic orientations of the magnetic resonance and then utilize a DC current through a straight wire antenna close to the waveguide to prove the sensor capabilities of our device. We reconstruct the complete vector magnetic field in the NV crystal frame using three different NV crystallographic orientations. By knowing the polarization axis of the waveguide mode, we project the magnetic field vector into the lab frame.
High Resolution Image Download MS PowerPoint Slide Ensemble negatively charged nitrogen-vacancy centers in diamond are promising quantum sensors. To optimize their sensitivity, it is crucial to increase the number of spins sampled and maximize their coupling to the detection system without degrading their spin properties. In this paper, we demonstrate enhanced quantum magnetometry via a buried laser-written waveguide in diamond with 4.5 ppm nitrogen-vacancy centers. The waveguide-coupled nitrogen-vacancy centers exhibit spin coherence properties comparable to those of nitrogen-vacancy centers in pristine diamond. Waveguide-enhanced magnetic field sensing is demonstrated in a fiber-coupled integrated photonic chip, where probing an increased volume of high-density spins results in 63 pT·Hz –1/2 of DC magnetic field sensitivity and 20 pT·Hz –1/2 of AC magnetic field sensitivity. This on-chip sensor realizes at least an order of magnitude improvement in sensitivity compared to the conventional confocal detection setup, paving the way for high-sensitivity quantum magnetometry with nitrogen-vacancy ensembles.
Nitrogen vacancy (NV) centers in diamonds can function as quantum sensors for measuring magnetic fields, temperature, and stress with high sensitivity. They are useful in various biological applications, such as for measuring the local magnetic and electrical fields and signal propagation in tissues as well as their local interaction dynamics. However, to enable measurements suitable for medical applications, an observation system that can noninvasively map neural activity from the magnetic fields generated by brain nerve cells with high spatial resolution and sensitivity is required. We fabricated a vertical waveguide array in a diamond containing nitrogen vacancy (NV) centers with cell size dimension using a green femtosecond Bessel beam laser. The red emission from NV centers within the waveguide is confined inside the waveguide (typically with a cell size of 15 μm) by the total internal reflection at its walls. This enables efficient optical confinement and improves the light collection performance of the NV center emission. We have also developed a sensor—called the diamond micro-NV center array device (MAED)—that allows the observation of local magnetic field distributions and have measured spatial distribution of magnetic field with cell-size accuracy. This approach makes it possible to perform localized measurements of electrical and magnetic properties, as well as dynamic mapping of biological systems. This technological innovation holds a significant potential for the noninvasive observation of functional networks in cortical neurons.
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.
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.
Diamond’s nitrogen-vacancy (NV) center has been shown as a promising candidate for sensing applications and quantum computing because of its long electron spin coherence time and its ability to be found, manipulated and read out optically. An integrated photonics platform in diamond would be useful for NV-based magnetometry and quantum computing, in which NV centers are optically linked for long-range quantum entanglement due to the integration and stability provided by monolithic optical waveguides. Surface microchannels in diamond would be a great benefit for sensing applications, where NV centers could be used to probe biomolecules. In this work, we applied femtosecond laser writing to form buried 3D optical waveguides in diamond. By engineering the geometry of the type II waveguide, we obtained single mode guiding from visible to the infrared wavelengths. Further, we demonstrate the first Bragg waveguide in bulk diamond with narrowband reflection. We show the formation of single, high quality NV centers on demand in ultrapure diamond using a single pulse from a femtosecond laser. With these building blocks in place, we fabricated an integrated quantum photonic circuit containing optical waveguides coupled to NV centers deterministically placed within the waveguide. The single NVs were excited and their emission collected by the optical waveguides, allowing easy interfacing to standard optical fibers. We also report high aspect ratio surface microchannels, which we will integrate with laser-written NVs and waveguides, paving the way for ultrasensitive, nanoscale resolution biosensors.