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High sensitivity fiber-integrated broadband magnetometry and thermometry using NV centers in a femtosecond laser-written diamond waveguide

Demininggus Pekei, Yanzhao Guo, Giulio Coccia, Argyro N. Giakoumaki, Roberta Ramponi, Anthony J. Bennett, Shane Michael Eaton, John Patrick Hadden

Published Sep 30, 2026• 0 citations
OpenAlex

Abstract

We investigate realistic fiber-integrated broadband magnetometry and thermometry with projected shot-noise-limited DC-sensitivity of up to 63 pT/√Hz, based on dense NV center ensembles in a femtosecond laser-written diamond waveguide using balanced photodiodes.

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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.
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.
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 58 nT/Hz58\,\text{nT}/\sqrt{\text{Hz}}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.
Diamond's nitrogen vacancy (NV) center is an optically active defect with long spin coherence times, showing potential for efficient nanoscale magnetometry and entanglement schemes. Recently, both the formation of buried 3D optical waveguides and high quality single NVs in diamond were demonstrated using femtosecond laser-writing. However, until now, combining these technologies has been an outstanding challenge. In this work, we fabricate laser-written photonic circuits in diamond aligned within micron resolution to single laser-written NVs, enabling an integrated platform providing deterministically positioned waveguide-coupled NVs. This fabrication technology opens the way towards on-chip optical routing of single photons between NVs and optically integrated spin-based magnetometry.
The nitrogen-vacancy (NV) center in diamond is a prime candidate for quantum sensing technologies. Here, we present a fully integrated and mechanically robust fiber-based endoscopic sensor with a tip diameter of 1.25 mm . On its tip, a direct laser-writing process is used to secure a diamond containing NV centers above the fiber’s core inside a polymer structure. Additionally, a metallic direct laser-written antenna structure next to the fiber facet allows efficient microwave manipulation of NV-center spins. The sensor achieves a shot-noise-limited magnetic-field sensitivity of 5.9 nT / Hz using a 15 − μ m -sized microdiamond at a microwave power of 50 mW and an optical power of 2.15 mW . Using lock-in techniques, we measure a sensitivity of 51.8 nT / Hz . Furthermore, we introduce a dual-fiber concept that enables, in combination with a direct laser-written structure, independent guiding of excitation and fluorescence light and thus reduces background autofluorescence. Moreover, controlled guiding of excitation light to the diamond while avoiding sample illumination may enable operation in light-sensitive environments such as biological tissue. While the demonstrated sensitivity is achieved using a single-fiber configuration, the dual-fiber approach provides a path toward integrating smaller diamonds, where autofluorescence would otherwise limit performance. We demonstrate the capability of vector magnetic-field measurements in the type of magnetic field used in state-of-the-art ultracold quantum gas experiments, opening a potential arena in which high resolution and high sensitivity are required.