Quantum Sensing and Nano Electronics and Photonics
CMOS-integrated optical quantum sensing platform based on NV-diamond technology
Patrick Engelmann, Philipp Wartenberg, Josephine Mütze, Martin Blasl, Andreas Fritscher, Hayden Jeffrey Binger, Young‐Gwan Choi, Lotte M. Boer, Uri Vool, Uwe Vogel
Optical quantum sensors relying on spin resonance in nitrogen vacancy (NV)-diamond centers achieve exceptional sensitivity for measuring magnetic fields and other parameters at room temperature. Their increased precision enables previously impossible applications. However, current quantum sensors typically rely on bulky external lasers, microwave sources and complex optical configurations, constraining portable and large-scale deployments. This paper introduces a universal platform for optical quantum sensing that adapts CMOS compatible processes traditionally used in OLED-on-silicon fabrication to integrate complete optical quantum sensor elements into a CMOS microchip. By embedding light sources, antennas, and photodiodes in a layered structure, the system enables significant miniaturization, lower power consumption and enhanced robustness due to its solid-state architecture. The proposed concept enables a high degree of modularity and the realization of both single-sensor and array configurations. The envisioned architecture allows large-scale wafer-level production at relatively low cost and therefore broadens the potential use cases for optical quantum sensors.
Optical quantum sensors relying on spin resonance in nitrogen vacancy (NV)-diamond centers achieve exceptional sensitivity for measuring magnetic fields and other parameters at room temperature. Their increased precision enables previously impossible applications. However, current quantum sensors typically rely on bulky external lasers, microwave sources and complex optical configurations, constraining portable and large-scale deployments. This paper introduces a universal platform for optical quantum sensing that adapts CMOS compatible processes traditionally used in OLED-on-silicon fabrication to integrate complete optical quantum sensor elements into a CMOS microchip. By embedding light sources, antennas, and photodiodes in a layered structure, the system enables significant miniaturization, lower power consumption and enhanced robustness due to its solid-state architecture. The proposed concept enables a high degree of modularity and the realization of both single-sensor and array configurations. The envisioned architecture allows large-scale wafer-level production at relatively low cost and therefore broadens the potential use cases for optical quantum sensors.
We report progress toward a CMOS-integrated quantum diamond biosensing platform that combines nitrogen-vacancy (NV) centers in diamond with a custom 40 nm CMOS Single-Photon Avalanche Diode (SPAD) array. The system integrates on-chip active quenching and digital readout with external FPGA-based photon counting, compact microwave delivery, and practical optical excitation and collection schemes to support widefield optically detected magnetic resonance (ODMR). System-level design considerations spanning fluorescence collection efficiency, detector count-rate capability, and microwave homogeneity are analyzed with biological compatibility and scalability in mind. Using superparamagnetic iron oxide nanoparticle (SPION)-labeled HEK293T cells as a representative use case, simple dipole-field estimates indicate that sub-μT sensitivity is required to resolve ODMR shifts within typical ensemble linewidths. Based on the proposed architecture and efficiency analysis, a magnetic field sensitivity of approximately 90 nT/Hz per pixel is estimated. These results outline a practical path from optics-heavy quantum diamond microscopes toward compact, CMOS-integrated NV-based biosensors for quantitative magnetic imaging in complex biological environments.
Color centers are defects within crystals that trap charge carriers in optically accessible levels. In diamonds, these color centers hold great potential for use in quantum sensing and quantum information. The utilization of the nitrogen vacancy (NV) center situated within diamond has allowed demonstrations of magnetic field, electric field, strain, and temperature sensors [1]. In more recent times, the investigation of color centers employing group-IV elements, such as SiV, GeV, and SnV, has gained interests [2]. This interest is attributed to their zero electric dipole moment and diminished optical transition fluctuations, as shown in Fig. 1. However, the manipulation and detection of color centers requires unwieldy and discrete commercial apparatus, leading to a large overall footprint and imposing constraints upon its practical utility. To address this issue, a CMOS-integrated quantum sensor based on loop inductors [3], and a quantum magnetometer using scalable inductor array and photonic filter [4] have been proposed for NV operating at room temperature (RT). In [3], the on-chip photonic filter attenuates the influence of the green laser excitation at a ratio of 10dB, concurrently with the on-chip photodiode (PD) detection of the red fluorescence stemming from the NV center excitation. [4] subsequently enhances this suppression to 25dB for green light. Nevertheless, both [3] and [4] suffer from the red fluorescence emitted by the top passivation on the CMOS chip, which is also excited by the laser (Fig. 2). The photonic filter cannot eliminate this undesired passivation layer's fluorescence because it shares the same frequency as the color center fluorescence. Thus, the top passivation layer must be etched before taking measurements. However, etching the passivation can introduce more defects in the underlying layers, leading to increased randomness and making it more challenging to control the fluorescence. Besides, the scope of effectiveness attributed to on-chip photonic filters encounters constraints in the context of other variants of color centers. The NV can be excited using an off-resonant 532 nm laser, and the intensity of the broad emission from 637 to 780nm is spin state dependent, allowing the scattered excitation light to be spectrally filtered during spin readout. The group IV emitters do not allow off-resonant readout of the spin state, so resonant excitation that matches the frequency of must be used, making spectral filtering more challenging, as shown in Fig. 1. This paper introduces a CMOS-integrated control and detection system capable of functioning at both room and cryogenic temperatures.
Quantum sensors based on the nitrogen-vacancy (NV) center in diamond are leading platforms for high-sensitivity magnetometry with nanometer-scale resolution. State-of-the-art implementations, however, typically rely on bulky free-space optics or sacrifice spatial resolution to achieve high sensitivities. Here, we realize an integrated platform that overcomes this trade-off by fabricating monolithic whispering-gallery-mode cavities from a diamond chip containing a high density of NV centers and by evanescently coupling excitation to and photoluminescence from the cavity using a tapered optical fiber. Employing a lock-in-amplified Ramsey magnetometry scheme, we achieve a photon-shot-noise-limited DC sensitivity of 58nT/Hz---the best sensitivity reported to date for a nanofabricated cavity-based magnetometer. The microscopic cavity size enables micrometer-scale spatial resolution and low-power operation, while fiber-coupling provides a path to scalable on-chip integration. Arrays of such sensors could enable NV-NMR spectroscopy of sub-nanoliter samples, new magnetic-gradient imaging architectures, and compact biosensing platforms.
Quantum sensors encompass a diverse class of devices that exploit quantum coherence to detect weak or nanoscale signals. As their behavior is tied to physical constants, quantum sensors can achieve accuracy, repeatability, and precision approaching fundamental limits [1, 2]. As a result, these sensors have shown utility in a wide range of applications in both science and engineering leading to innovations. Among many solid-state spin systems, nitrogen-vacancy (NV) centers in diamonds have attracted considerable attention as a leading platform in many fields of quantum technologies, from quantum sensing to information processing and communication applications. They have superior physical properties, and their quantum coherence is preserved even at room temperature. The energy levels of NV centers are sensitive to magnetic fields, electric fields, strain, and temperature, and the spatial resolution is scalable from nanometers to millimeters. Therefore, diamond quantum sensors are distinctive sensors with multimodality and span scalable application fields. To realize an ideal quantum sensor for applications, the technical challenges in the sensor materials and the quantum control techniques, such as coherent microwave spin manipulation, effective optical spin-state initialization, and readout, have been developed. This chapter briefly explains the sensing principle using NV centers and then introduces sensor systems for biomedical applications, and monitoring of batteries for electric vehicles and internal power devices.
Diamond NV centers have transformed quantum sensing by enabling precise measurement of magnetic and electric fields, temperature, pressure, and strain, all within a reliable solid-state platform, at room temperature, down to the nanoscale. These capabilities position NV-based sensors as alternatives to cryogenic SQUIDs or atomic gas systems, with transformative potential across biomedical imaging, autonomous navigation, and industrial non-destructive testing (NDT). Despite promising prototypes—such as fiber-integrated endoscopes, CMOS-compatible sensors, and microfluidic chips—the development of widescale applications is hampered due to challenges in diamond micro/nanofabrication and photonic integration. Our group addresses these limitations through diamond processing techniques and hybrid material platforms. We develop methods for fabricating quantum-grade diamond nanostructures, including nanopillars optimized for neuronal electric field sensing and other photonic cavity applications. Additionally, we explore the integration of NV-rich diamond membranes within photonic systems to improve the spin photon interaction and efficient conversion of the pump beam. Collaborating with industry partner Kwantek, we also work on a compact fiber-endoscope prototype enabling NDT in constrained environments. These innovations will improve the state-of-the-art NV magnetometry to reduce system footprint and cost, critical for future industrialisation.
This dissertation presents the development and characterization of fully integrated quantum sensors based on nitrogen vacancy (NV) centers in diamond. While existing NV-based sensors are typically large and complex, this work focuses on miniaturizing the technology and demonstrating its application as a current sensor. The primary research question addressed is whether fully integrated NVbased quantum sensors with LED excitation can be realized with performance comparable to conventional sensor technologies. To this end, two sensor prototypes were developed: one as the smallest fully integrated NV quantum sensor with a complete electrical interface to date, achieving a sensitivity of 32 nT/ √ Hz; and another as the first NV-based sensor implemented on a flexible PCB, which is even smaller and achieves a sensitivity of 96 nT/ √ Hz. Thereby both sensors utilize randomly oriented diamond microcrystals. Methodologically, a novel procedure for determining the orientation of the diamond crystals was developed, allowing for effective signal extraction despite the random crystal orientation. Further, magnetic fields were simulated using COMSOL Multiphysics to investigate the feasibility of applying these sensors for current measurements. In this context, a new measurement concept for determining currents in segmented multi-wire cables of three-phase power grids was developed, demonstrating the potential of NV-based sensors in smart grid applications. The results indicate that these quantum sensors can be more easily integrated, even when diamonds are placed arbitrarily, thus paving the way for new applications in smart grid monitoring and other fields requiring compact, high-precision magnetic field sensors.