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arXiv:2406.15450 · Physical Review Applied

Quantum diamond microscope for narrowband magnetic imaging with high spatial and spectral resolution

Zechuan Yin, Jiashen Tang, Connor Hart, John W. Blanchard, Xinyan Xiang, Saipriya Satyajit, Smriti Bhalerao, Tao Tao, Stephen J. DeVience, Ronald Lee Walsworth

Published Nov 18, 2024• 9 citations
arXivHTMLPDF

Abstract

The quantum diamond microscope (QDM) is a versatile, widely used platform for magnetic field imaging, but in applications it has been limited to broadband signals. This study integrates a QDM with a narrowband measurement protocol and a fast lock-in camera, enabling imaging of rf magnetic field patterns with micrometer-scale spatial resolution, single-hertz spectral resolution, and nanotesla sensitivity for each pixel. The rf QDM simultaneously images the amplitude, frequency, and phase of narrowband fields, for potential applications in micrometer-scale NMR imaging, ac-susceptibility mapping, impedance tomography, electronic circuit analysis, and spatial eddy-current inspection.

DOI
10.1103/physrevapplied.22.054050

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The quantum diamond microscope (QDM) is a versatile, widely used platform for magnetic field imaging, but in applications it has been limited to broadband signals. This study integrates a QDM with a narrowband measurement protocol and a fast lock-in camera, enabling imaging of rf magnetic field patterns with micrometer-scale spatial resolution, single-hertz spectral resolution, and nanotesla sensitivity for each pixel. The rf QDM simultaneously images the amplitude, frequency, and phase of narrowband fields, for potential applications in micrometer-scale NMR imaging, ac-susceptibility mapping, impedance tomography, electronic circuit analysis, and spatial eddy-current inspection.
Wide-field imaging of magnetic signals using ensembles of nitrogen-vacancy (NV) centers in diamond has garnered increasing interest due to its combination of micron-scale resolution, millimeter-scale field of view, and compatibility with diverse samples from across the physical and life sciences. Recently, wide-field NV magnetic imaging based on the Ramsey protocol has achieved uniform and enhanced sensitivity compared to conventional measurements. Here, we integrate the Ramsey-based protocol with spin-bath driving to extend the NV spin dephasing time and improve magnetic sensitivity. We also employ a high-speed camera to enable dynamic wide-field magnetic imaging. We benchmark the utility of this quantum diamond microscope (QDM) by imaging magnetic fields produced from a fabricated wire phantom. Over a 270 × 270 μm2 field of view, a median per-pixel magnetic sensitivity of 4.1(1) nT /Hz is realized with a spatial resolution ≲ 10 μm and sub-millisecond temporal resolution. Importantly, the spatial magnetic noise floor can be reduced to the picotesla scale by time-averaging and signal modulation, which enables imaging of a magnetic-field pattern with a peak-to-peak amplitude difference of about 300 pT. Finally, we discuss potential new applications of this dynamic QDM in studying biomineralization and electrically active cells.
Abstract Quantum systems composed of solid-state electronic spins can be sensitive detectors of narrowband magnetic fields. A prominent example is the nitrogen-vacancy (NV) center in diamond, which has been employed for magnetic spectroscopy with high spatial and spectral resolution. However, NV-diamond spectroscopy protocols are typically based on dynamical decoupling sequences, which are limited to low-frequency signals (≲ 20 MHz) due to the technical requirements on microwave (MW) pulses used to manipulate NV electronic spins. In this work, we experimentally demonstrate a high-resolution magnetic spectroscopy protocol that integrates a quantum frequency mixing (QFM) effect in a dense NV ensemble with coherently averaged synchronized readout (CASR) to provide both a wide range of signal frequency detection and sub-Hz spectral resolution. We assess the sensitivity of this QFM-CASR protocol across a frequency range of 10 MHz to 4 GHz. By measuring the spectra of multi-frequency signals near 0.6, 2.4 and 4 GHz, we demonstrate sub-Hz spectral resolution with a nT-scale noise floor for the target signal, and precise phase measurement with error <1°. Compared to state-of-the-art NV-diamond techniques for narrowband magnetic spectroscopy, the QFM-CASR protocol greatly extends the detectable frequency range, enabling applications in high-frequency radio frequency (RF) and MW signal microscopy and analysis, as well as tesla-scale nuclear magnetic resonance (NMR) spectroscopy of small samples.
Wide-field quantum magnetometry using nitrogen-vacancy (NV) center in diamond can be a breakthrough for a nuclear magnetic resonance (NMR) in a small volume, which is important for biological applications. Although the coherence time of the electron spin of the NV center results in a limited frequency resolution for diamond magnetometry in the range 10–100 kHz, recent studies have shown that a phase-sensitive protocol can circumvent this limit using a confocal setup. We proposed a new measurement protocol, “iQdyne,” which facilitates an improved frequency resolution of wide-field imaging, unencumbered by the coherence limit imposed by the NV center. We demonstrated wide-field magnetometry with a frequency resolution of 238 mHz and a magnetic sensitivity of 65 nT/Hz1/2, which are superior to those obtained using a conventional XY8-based technique, and showed the potential of the iQdyne protocol for the wide-field NMR imaging.
Abstract Quantum sensing based on nitrogen-vacancy centers in diamond has shown excellent properties. Combined with the imaging technique, it shows exciting practicability. Here, we demonstrate the simultaneously imaging technique of magnetic field and temperature using a wide-field quantum diamond microscope. We describe the operating principles of the diamond microscope and report its sensitivity (magnetic field ${\sim}1.8~\mu \mbox{T/Hz}^{1/2}$ ∼ 1.8 μ T/Hz 1 / 2 and temperature ${\sim}0.4~\mbox{K/Hz}^{1/2}$ ∼ 0.4 K/Hz 1 / 2 ), spatial resolution (1.3 μm), and field of view ( $400 \times 300~\mu \mbox{m}^{2}$ 400 × 300 μ m 2 ). Finally, we use the microscope to obtain images of an integrated cell heater and a PCB, demonstrating its ability in the application of magnetic field and temperature simultaneously imaging at wide-field.
Quantum systems composed of solid-state electronic spins can be sensitive detectors of narrowband magnetic fields. A prominent example is the nitrogen-vacancy (NV) center in diamond, which has been employed for magnetic spectroscopy with high spatial and spectral resolution. However, NV-diamond spectroscopy protocols are typically based on dynamical decoupling sequences, which are limited to low-frequency signals ( ≲ 20 MHz) due to the technical requirements on microwave (MW) pulses used to manipulate NV electronic spins. In this work, we experimentally demonstrate a high-resolution magnetic spectroscopy protocol that integrates a quantum frequency mixing (QFM) effect in a dense NV ensemble with coherently averaged synchronized readout (CASR) to provide both a wide range of signal frequency detection and sub-Hz spectral resolution. We assess the sensitivity of this QFM-CASR protocol across a frequency range of 10 MHz to 4 GHz. By measuring the spectra of multi-frequency signals near 0.6, 2.4 and 4 GHz, we demonstrate sub-Hz spectral resolution with a nT-scale noise floor for the target signal, and precise phase measurement with error < 1 ∘ . Compared to state-of-the-art NV-diamond techniques for high-resolution magnetic spectroscopy, the QFM-CASR protocol extends the signal frequency range by more than an order of magnitude, enabling applications in radio frequency (RF) and MW signal microscopy and analysis, as well as tesla-scale nuclear magnetic resonance (NMR) spectroscopy of small samples.
Spectroscopic analysis of AC magnetic signal using diamond quantum magnetometry is a promising technique for inductive imaging. Conventional dynamic decoupling like XY8 provides a high sensitivity of an oscillating magnetic signal with intricate dependence on magnitude and phase, complicating high throughput detection of each parameter. In this study, a simple measurement scheme for independent and simultaneous detection of magnitude and phase is demonstrated by a sequential measurement protocol. Wide-field imaging experiment was performed for an oscillating magnetic field with approximately [Formula: see text]-squared observation area. Single pixel phase precision was [Formula: see text] for [Formula: see text] AC magnetic signal. Our method enables potential applications including inductive inspection and impedance imaging.