Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Applied Physics Letters

Achieving strain-limited ensemble dephasing times in solid-state quantum sensor with a compact single magnet assembly

Y. MASUYAMA, Chikara Shinei, Haruki Tanaka, Hiroshi Abe, Takashi Taniguchi, Masashi Miyakawa, Tokuyuki Teraji, Akihiro Kuwahata

Published Sep 28, 2026• 0 citations
Publisher

Abstract

Solid-state quantum sensors offer the promising prospect of high-sensitivity sensing across various environments, including at room temperature and atmospheric pressure. Highly sensitive solid-state quantum sensors require long ensemble dephasing times (T2*) in mm-scale sample areas. This requirement demands a highly uniform bias magnetic field across all qubits, which has traditionally required large magnetic field sources such as Helmholtz coils or a pair of magnets. Meanwhile, to expand the range of applications of quantum sensors, portable sensors are required, but it is difficult to carry these large magnets. Balancing the miniaturization of the quantum sensor with high sensitivity is a significant challenge. In this study, we achieve a long ensemble dephasing time for nitrogen-vacancy (NV) centers in a large sample volume using a single, compact, and optimized magnet assembly. By using a magnet design derived from an inverse problem-based analysis, we reduced the magnet assembly volume to 0.23% of the Helmholtz coil volume. We achieve an ensemble dephasing time of 5.32 μs for the entire NV center ensemble across the sample thickness, comparable to that obtained with a standard Helmholtz coil setup. This dephasing is limited by strain-induced dephasing across the diamond sample thickness, with a dephasing rate of 188 kHz, which represents the state-of-the-art diamond quality for bulk quantum sensors. Our work paves the way for the miniaturization of high-sensitivity quantum sensors, enabling new sensor designs and the construction of compact, highly sensitive quantum sensor arrays.

DOI
10.1063/5.0317515

Related papers

Unraveling quantum dephasing of nitrogen-vacancy center ensembles in diamond

Jixing Zhang, Cheuk Kit Cheung, Michael Kübler +16 more

Abstract Nitrogen-vacancy (NV) center ensembles in diamond are one of the most promising solid-state quantum platforms for various sensing applications. Achieving ultimate sensitivity requires simultaneously long spin dephasing times ( $${T}_{2}^{* }$$ T 2 * ) and high NV center concentrations. In this work, we propose a systematic measurement approach to quantify the electron spin dephasing in NV center ensembles and analyze the contributions of various sources to the dephasing time, including NV-NV interactions, strain and electric field distributions, 13 C nuclear spins, and P1 electron spins. Our method is validated using a series of high-performance diamond samples, providing a comprehensive understanding of dephasing mechanisms and revealing correlations between NV concentration and different dephasing sources. Building on these insights, we outline strategies to further enhance the achievable sensitivity for DC magnetic field measurements.

npj Quantum Materials•Mar 12, 2026•3 citations

Extension of Spin Dephasing Time of Millimeter Scale Ensemble NV centers by Suppressing Magnetic and Strain Field Inhomogeneities

Ikuya Fujisaki, Li Zehan, Yuji Hatano +11 more

Quantum magnetic sensors based on nitrogen-vacancy (NV) centers in diamond are expected to be applicable to biological and chemical applications However, their DC magnetic field sensitivity is still insufficient for demanding applications such as magnetoencephalography requiring extraordinary sensitivity. The spin dephasing time 𝑇2∗ is a key parameter to improve the sensitivity, but 𝑇2∗ of typical millimeter-scale NV centers is limited by magnetic field inhomogeneity, strain field inhomogeneity, and electronic spin bath. In this work, we developed (i) a magnet system suppressing both the longitudinal magnetic field and transverse strain field inhomogeneities and (ii) a microwave (MW) and radio-frequency (RF) application system for high-efficiency spin-bath driving (SBD) suitable for a diamond (111) sample.

•Oct 22, 2024•0 citations

Sensitive ac and dc magnetometry with nitrogen-vacancy-center ensembles in diamond

John F. Barry, Matthew Steinecker, Scott T. Alsid +4 more

Quantum sensing with solid-state spins offers the promise of high spatial resolution, bandwidth, and dynamic range at sensitivities comparable to more mature quantum sensing technologies, such as atomic vapor cells and superconducting devices. However, despite comparable theoretical sensitivity limits, the performance of bulk solid-state quantum sensors has so far lagged behind these more mature alternatives. A recent review [Barry et al., Rev. Mod. Phys. 92, 015004 (2020)] suggests several paths to improve performance of magnetometers employing nitrogen-vacancy defects in diamond, the most-studied solid-state quantum sensing platform. Implementing several suggested techniques, we demonstrate the most sensitive nitrogen-vacancy-based bulk magnetometer reported to date. Our approach combines tailored diamond growth to achieve low strain and long intrinsic dephasing times, the use of double-quantum Ramsey and Hahn-echo magnetometry sequences for broadband and narrowband magnetometry, respectively, and P1 driving to further extend dephasing time. Notably, the device does not include a flux concentrator, preserving the fixed response of the nitrogen vacancies to magnetic field. The magnetometer realizes a minimum sensitivity of $460\phantom{\rule{0.2em}{0ex}}\mathrm{fT}\phantom{\rule{0.2em}{0ex}}{\mathrm{s}}^{1/2}$ in a broadband dc-sensitive mode and $210\phantom{\rule{0.2em}{0ex}}\mathrm{fT}\phantom{\rule{0.2em}{0ex}}{\mathrm{s}}^{1/2}$ in a narrowband ac mode. We describe the experimental setup in detail and highlight potential paths for future improvement.

arXiv:2305.06269•Physical Review Applied•Oct 25, 2024•87 citations

High-Precision Mapping of Diamond Crystal Strain Using Quantum Interferometry

Mason C. Marshall, Reza Ebadi, Connor Hart +4 more

Crystal-strain variation imposes significant limitations on many quantum sensing and information applications for solid-state defect qubits in diamond. Thus, the precision measurement and control of diamond crystal strain is a key challenge. Here, we report diamond strain measurements with a unique set of capabilities, including micron-scale spatial resolution, a millimeter-scale field of view, and a 2-order-of-magnitude improvement in volume-normalized sensitivity over previous work, reaching $5(2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}/\sqrt{\mathrm{Hz}\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}{\mathrm{m}}^{\ensuremath{-}3}}$ (with spin-strain coupling coefficients representing the dominant systematic uncertainty). We use strain-sensitive spin-state interferometry on ensembles of nitrogen-vacancy ($\mathrm{N}$-$V$) color centers in single-crystal bulk diamond with low strain gradients. This quantum interferometry technique provides insensitivity to magnetic-field inhomogeneity from the electronic and nuclear spin bath, thereby enabling long $\mathrm{N}$-$V$--ensemble electronic spin dephasing times and enhanced strain sensitivity, as well as broadening the potential applications of the technique beyond isotopically enriched or high-purity diamond. We demonstrate the strain-sensitive measurement protocol first on a confocal scanning laser microscope, providing quantitative measurement of sensitivity as well as three-dimensional strain mapping; and second on a wide-field-imaging quantum diamond microscope. Our strain-microscopy technique enables fast, sensitive characterization for diamond material engineering and nanofabrication; as well as diamond-based sensing of strains applied externally, as in diamond anvil cells or embedded diamond stress sensors, or internally, as by crystal damage due to particle-induced nuclear recoils.

arXiv:2108.00304•Physical Review Applied•Feb 15, 2022•31 citations

Homogeneous spin-dephasing time of NV− centre in millimetre-scale 12C-enriched high-pressure high-temperature diamond crystals

Chikara Shinei, Y. MASUYAMA, Hiroshi Abe +4 more

Negatively charged nitrogen vacancy (NV−) centres in diamond crystals are promising colour centres for high-sensitivity quantum sensors. A long dephasing time (T2* > 10 μs) is essential for achieving increased sensitivity and higher uniformity of T2* in millimetre-scale diamond is strongly desired for femto-tesla weak magnetic field detection. High uniformity of T2* for NV− centres is achieved herein. The median value of T2*, <T2*>, in the 12C-enriched high-pressure, high-temperature (HPHT) grown diamond with a nitrogen concentration of 1.3 ± 0.4 ppm is 4.5 μs. The variance of T2* is only 10% over a millimetre-scale region (1.1 × 1.1 mm2) within the 0.4 mm thick {111} growth sector. <T2*> is ~2/3 times the value limited by the dipole-dipole interaction from the electron-spin bath of nitrogen impurities, suggesting that the residual strain gradient in the HPHT diamond crystal partially limits T2*. Reducing the strain gradient in diamond crystals provide a pathway to achievement of high sensitivity magnetometry using NV quantum sensing. Negatively charged nitrogen vacancy centres in diamond crystals are promising for achieving high-sensitivity quantum sensors. Here, a long dephasing time with high uniformity is achieved in a millimetre-scale area along the {111} plane using 12C enriched high-pressure high-temperature diamond crystals.

Communications Materials•Apr 8, 2025•7 citations

Enhancing quantum sensing performance by optimizing the concentration and dephasing time of the NV ensemble in CVD-diamond

Sixian Wang, Guodong Bian, Pengcheng Fan +3 more

The negatively charged nitrogen−vacancy (NV − ) center ensembles in diamonds offer enormous potential for developing integrated sensors with an improved signal-to-noise ratio (SNR) and high sensitivity. However, the preparation and treatment of diamond samples with suitable NV − concentrations and dephasing time have remained challenging. This work provided insight into the NV − center formation mechanism and reconstruction via a comprehensive analysis of the concentration and dephasing time of a set of diamond samples treated by various parameters. By varying the electron irradiation dose and subsequent annealing duration, the conversion rate of nitrogen to NV − is up to 18.45%, and the corresponding maximum NV − concentration is 3.69 ppm. The dephasing time for all samples varies around 300 ns. The nitrogen-related NV − center ensemble dephasing rate per unit density is 146.4 (ppm·ms) −1 , indicating that the treatment did not substantially alter the paramagnetic spin environment around the NV − center. This study not only offers support to exquisite sensitivities of NV-based sensors but also provides valuable experience for the preparation of unique properties of synthetic diamonds.

Optical Materials Express•Dec 15, 2022•5 citations
Solid-state quantum sensors offer the promising prospect of high-sensitivity sensing across various environments, including at room temperature and atmospheric pressure. Highly sensitive solid-state quantum sensors require long ensemble dephasing times (T2*) in mm-scale sample areas. This requirement demands a highly uniform bias magnetic field across all qubits, which has traditionally required large magnetic field sources such as Helmholtz coils or a pair of magnets. Meanwhile, to expand the range of applications of quantum sensors, portable sensors are required, but it is difficult to carry these large magnets. Balancing the miniaturization of the quantum sensor with high sensitivity is a significant challenge. In this study, we achieve a long ensemble dephasing time for nitrogen-vacancy (NV) centers in a large sample volume using a single, compact, and optimized magnet assembly. By using a magnet design derived from an inverse problem-based analysis, we reduced the magnet assembly volume to 0.23% of the Helmholtz coil volume. We achieve an ensemble dephasing time of 5.32 μs for the entire NV center ensemble across the sample thickness, comparable to that obtained with a standard Helmholtz coil setup. This dephasing is limited by strain-induced dephasing across the diamond sample thickness, with a dephasing rate of 188 kHz, which represents the state-of-the-art diamond quality for bulk quantum sensors. Our work paves the way for the miniaturization of high-sensitivity quantum sensors, enabling new sensor designs and the construction of compact, highly sensitive quantum sensor arrays.
Abstract Nitrogen-vacancy (NV) center ensembles in diamond are one of the most promising solid-state quantum platforms for various sensing applications. Achieving ultimate sensitivity requires simultaneously long spin dephasing times ( T2∗{T}_{2}^{* }T2∗​ T 2 * ) and high NV center concentrations. In this work, we propose a systematic measurement approach to quantify the electron spin dephasing in NV center ensembles and analyze the contributions of various sources to the dephasing time, including NV-NV interactions, strain and electric field distributions, 13 C nuclear spins, and P1 electron spins. Our method is validated using a series of high-performance diamond samples, providing a comprehensive understanding of dephasing mechanisms and revealing correlations between NV concentration and different dephasing sources. Building on these insights, we outline strategies to further enhance the achievable sensitivity for DC magnetic field measurements.
Quantum magnetic sensors based on nitrogen-vacancy (NV) centers in diamond are expected to be applicable to biological and chemical applications However, their DC magnetic field sensitivity is still insufficient for demanding applications such as magnetoencephalography requiring extraordinary sensitivity. The spin dephasing time 𝑇2∗ is a key parameter to improve the sensitivity, but 𝑇2∗ of typical millimeter-scale NV centers is limited by magnetic field inhomogeneity, strain field inhomogeneity, and electronic spin bath. In this work, we developed (i) a magnet system suppressing both the longitudinal magnetic field and transverse strain field inhomogeneities and (ii) a microwave (MW) and radio-frequency (RF) application system for high-efficiency spin-bath driving (SBD) suitable for a diamond (111) sample.
Quantum sensing with solid-state spins offers the promise of high spatial resolution, bandwidth, and dynamic range at sensitivities comparable to more mature quantum sensing technologies, such as atomic vapor cells and superconducting devices. However, despite comparable theoretical sensitivity limits, the performance of bulk solid-state quantum sensors has so far lagged behind these more mature alternatives. A recent review [Barry et al., Rev. Mod. Phys. 92, 015004 (2020)] suggests several paths to improve performance of magnetometers employing nitrogen-vacancy defects in diamond, the most-studied solid-state quantum sensing platform. Implementing several suggested techniques, we demonstrate the most sensitive nitrogen-vacancy-based bulk magnetometer reported to date. Our approach combines tailored diamond growth to achieve low strain and long intrinsic dephasing times, the use of double-quantum Ramsey and Hahn-echo magnetometry sequences for broadband and narrowband magnetometry, respectively, and P1 driving to further extend dephasing time. Notably, the device does not include a flux concentrator, preserving the fixed response of the nitrogen vacancies to magnetic field. The magnetometer realizes a minimum sensitivity of 460fTs1/2460\phantom{\rule{0.2em}{0ex}}\mathrm{fT}\phantom{\rule{0.2em}{0ex}}{\mathrm{s}}^{1/2}460fTs1/2 in a broadband dc-sensitive mode and 210fTs1/2210\phantom{\rule{0.2em}{0ex}}\mathrm{fT}\phantom{\rule{0.2em}{0ex}}{\mathrm{s}}^{1/2}210fTs1/2 in a narrowband ac mode. We describe the experimental setup in detail and highlight potential paths for future improvement.
Crystal-strain variation imposes significant limitations on many quantum sensing and information applications for solid-state defect qubits in diamond. Thus, the precision measurement and control of diamond crystal strain is a key challenge. Here, we report diamond strain measurements with a unique set of capabilities, including micron-scale spatial resolution, a millimeter-scale field of view, and a 2-order-of-magnitude improvement in volume-normalized sensitivity over previous work, reaching $5(2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}/\sqrt{\mathrm{Hz}\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}{\mathrm{m}}^{\ensuremath{-}3}}$ (with spin-strain coupling coefficients representing the dominant systematic uncertainty). We use strain-sensitive spin-state interferometry on ensembles of nitrogen-vacancy (N\mathrm{N}N-VVV) color centers in single-crystal bulk diamond with low strain gradients. This quantum interferometry technique provides insensitivity to magnetic-field inhomogeneity from the electronic and nuclear spin bath, thereby enabling long N\mathrm{N}N-VVV--ensemble electronic spin dephasing times and enhanced strain sensitivity, as well as broadening the potential applications of the technique beyond isotopically enriched or high-purity diamond. We demonstrate the strain-sensitive measurement protocol first on a confocal scanning laser microscope, providing quantitative measurement of sensitivity as well as three-dimensional strain mapping; and second on a wide-field-imaging quantum diamond microscope. Our strain-microscopy technique enables fast, sensitive characterization for diamond material engineering and nanofabrication; as well as diamond-based sensing of strains applied externally, as in diamond anvil cells or embedded diamond stress sensors, or internally, as by crystal damage due to particle-induced nuclear recoils.
Negatively charged nitrogen vacancy (NV−) centres in diamond crystals are promising colour centres for high-sensitivity quantum sensors. A long dephasing time (T2* > 10 μs) is essential for achieving increased sensitivity and higher uniformity of T2* in millimetre-scale diamond is strongly desired for femto-tesla weak magnetic field detection. High uniformity of T2* for NV− centres is achieved herein. The median value of T2*, <T2*>, in the 12C-enriched high-pressure, high-temperature (HPHT) grown diamond with a nitrogen concentration of 1.3 ± 0.4 ppm is 4.5 μs. The variance of T2* is only 10% over a millimetre-scale region (1.1 × 1.1 mm2) within the 0.4 mm thick {111} growth sector. <T2*> is ~2/3 times the value limited by the dipole-dipole interaction from the electron-spin bath of nitrogen impurities, suggesting that the residual strain gradient in the HPHT diamond crystal partially limits T2*. Reducing the strain gradient in diamond crystals provide a pathway to achievement of high sensitivity magnetometry using NV quantum sensing. Negatively charged nitrogen vacancy centres in diamond crystals are promising for achieving high-sensitivity quantum sensors. Here, a long dephasing time with high uniformity is achieved in a millimetre-scale area along the {111} plane using 12C enriched high-pressure high-temperature diamond crystals.
The negatively charged nitrogen−vacancy (NV − ) center ensembles in diamonds offer enormous potential for developing integrated sensors with an improved signal-to-noise ratio (SNR) and high sensitivity. However, the preparation and treatment of diamond samples with suitable NV − concentrations and dephasing time have remained challenging. This work provided insight into the NV − center formation mechanism and reconstruction via a comprehensive analysis of the concentration and dephasing time of a set of diamond samples treated by various parameters. By varying the electron irradiation dose and subsequent annealing duration, the conversion rate of nitrogen to NV − is up to 18.45%, and the corresponding maximum NV − concentration is 3.69 ppm. The dephasing time for all samples varies around 300 ns. The nitrogen-related NV − center ensemble dephasing rate per unit density is 146.4 (ppm·ms) −1 , indicating that the treatment did not substantially alter the paramagnetic spin environment around the NV − center. This study not only offers support to exquisite sensitivities of NV-based sensors but also provides valuable experience for the preparation of unique properties of synthetic diamonds.