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Masahiro Ohkuma, Keigo Arai, Kenji Ohta, Toru Shinmei, [Ryo Matsumoto](https://orcid.org/0000-0001-6294-5403), [Yoshihiko Takano](https://orcid.org/0000-0002-1541-6928), Tetsuo Irifune

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[Optically detected magnetic resonance of nitrogen-vacancy centers in microdiamonds inside nanopolycrystalline diamond anvil cell](https://mdr.nims.go.jp/datasets/adde4355-d94e-4b20-8e4b-de4747aec52e)

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Optically detected magnetic resonance of nitrogen-vacancy centers in microdiamonds inside nanopolycrystalline diamond anvil cellOptically detected magnetic resonance of nitrogen-vacancy centers in microdiamondsinside nanopolycrystalline diamond anvil cellMasahiro Ohkuma1,∗ Keigo Arai1, Kenji Ohta2, Toru Shinmei3,Ryo Matsumoto4, Yoshihiko Takano4, and Tetsuo Irifune31School of Engineering, Institute of Science Tokyo, Yokohama 226-8501, Kanagawa, Japan2Department of Earth and Planetary Sciences, Institute of Science Tokyo, Meguro 152-8551, Tokyo, Japan3Geodynamics Research Center, Ehime University, Matsuyama, 790-8577, Ehime, Japan and4Research Center for Materials Nanoarchitectonics (MANA),National Institute for Materials Science, Tsukuba 305-0047, Ibaraki, Japan(Dated: February 24, 2026)We demonstrated optically detected magnetic resonance (ODMR) of nitrogen-vacancy (NV) cen-ters in microdiamonds inside a diamond anvil cell pressurized with nanopolycrystalline diamond(NPD) anvils. NPD exhibits high optical transparency, superior hardness, and low thermal con-ductivity, making it suitable for optical and spectroscopic measurements under high-pressure andhigh-temperature conditions. We observed the ODMR signal from an ensemble of NV centers un-der conditions where NV centers in microdiamonds served as markers for pressures exceeding 30GPa, with a culet diameter of 600 µm. We also performed ODMR measurements on multiple mi-crodiamonds sealed inside a sample chamber and found that the resonance frequency varied withthe pressure distribution. The combination of NPD and microdiamonds containing NV centers isauspicious for pressure and magnetic sensing under concurrent high-pressure and high-temperatureconditions.Recently, a negatively charged nitrogen-vacancy (NV)center, a point defect in diamond, has attracted consid-erable attention as a quantum sensor that can operateeven under high pressure [1–5]. The NV center carriesan electronic spin of S = 1, whose state can be co-herently manipulated using a microwave magnetic fieldtuned to resonance and optically read out via its redphotoluminescence intensity [6–9]. This magnetic reso-nance technique is known as optically detected magneticresonance (ODMR). Zero-field magnetic resonance is ob-served around 2.87 GHz under ambient conditions. Asshown in Fig. 1a, the ground state energy level is sensitiveto variations in temperature, magnetic field, and pres-sure, enabling the nanoscale imaging of these physicalquantities [1, 2, 10–20]. Magnetic and pressure sensingunder high-pressure conditions has been extensively per-formed using a diamond anvil cell (DAC) as the pressure-generating apparatus. Such measurements are typicallyrealized either by implanting NV centers near the sur-face of a single-crystalline diamond (SCD) anvil or by in-troducing nano- or micro-sized diamonds containing NVcenters into the sample chamber [1–3, 20–23]. In addi-tion, spatial pressure distributions inside DAC samplechambers have recently been investigated using NV cen-ters in nanodiamonds [24].Whereas SCD is typically employed as the anvil mate-rial in DAC, nanopolycrystalline diamond (NPD) is alsoa viable alternative. NPD is composed of fine grainsseveral tens of nanometers in a randomly oriented crys-tallographic orientation [25]. The optical transparencyof NPD is comparable to that of typical Type Ib SCD,making it suitable for optical and spectroscopic measure-∗ okuma.m.36c3@m.isct.ac.jpments under high pressure [26, 27]. In addition, NPD ex-hibits superior hardness and isotropic mechanical prop-erties owing to the absence of cleavage planes, enablingthe generation of ultrahigh pressures, even with largeculet sizes. This capability is particularly advantageousin experiments that require large sample volumes, such asneutron diffraction [28–30]. Furthermore, NPD can ex-hibit a thermal conductivity nearly an order of magnitudelower than that of typical SCD, which facilitates retain-ing higher temperatures in the sample chamber [31, 32].When combined with laser heating, this characteristic al-lows the sample chamber within the DAC to be heatedto temperatures exceeding 5000 K [33]. In high-pressureexperiments employing NPD anvils, pressure estimationbased on the edge of the diamond Raman shift, com-monly used with SCD anvils, is challenging [34]. Instead,pressure is typically determined using the ruby fluores-cence scale.Despite these advantages of NPD anvils, there havebeen no reports on their integration with NV centers,which can provide local information on the strain, mag-netic field, and temperature. However, realizing ODMR-based NV sensing in an NPD–DAC is non-trivial becauseNPD can introduce additional scattering and backgroundluminescence, which can reduce fluorescence collection ef-ficiency and ODMR contrast. In this study, we employedmicrodiamonds (MDs) containing ensembles of NV cen-ters in conjunction with NPD anvils as an alternativepressure gauge to the ruby fluorescence method. Wedemonstrated the ODMR of these MDs inside a DACpressurized using NPD anvils. We observed the mag-netic resonance of NV centers under high pressure, underconditions where NV centers in MDs served as markersfor pressures exceeding 30 GPa, with a relatively largecuret diameter of 600 µm. We also performed ODMR onarXiv:2507.13634v2  [cond-mat.mtrl-sci]  23 Feb 2026mailto:okuma.m.36c3@m.isct.ac.jphttps://arxiv.org/abs/2507.13634v22multiple MDs sealed inside the sample space and foundthat the resonance frequency varied with the pressuredistribution. These findings highlight the significant po-tential of combining NPD with NV-containing MDs forlocalized pressure and magnetic sensing under extremelyhigh-pressure and high-temperature conditions.High-pressure generation was achieved using the DAC.An overview of the setup is illustrated in Fig. 1b. Weused two opposing NPD anvils with culet sizes of 600µm. A gasket of rhenium was pre-indented from 250 µmto 50–60 µm, and a 200 µm diameter hole was drilled.Subsequently, we prepared a slit to create a gasket witha Lenz lens [2, 35, 36]. To prevent deformation of the slitby pressure, the sample space and slit were filled witha cBN and TiO2 mixture, and the gasket was pressur-ized. After the pressure was released, the cBN and TiO2mixture in the sample space was removed. The samplespace was then filled with a liquid pressure-transmittingmedium, glycerol, and sealed with the NPD anvil, whichhad several MDs on the culet surface. We used MD of15–25 µm diameter with 3.5 ppm NV center, purchasedfrom Adamas Nanotechnologies. Some contamination ofcBN and TiO2 mixtures were remained in the samplespace during the sealing process. A 1.5-turn copper loopcoil was placed around the anvil to apply a microwavemagnetic field. For wide-field ODMR measurements, arhenium gasket was pre-indented from 250 µm to 50–60µm, and a 300-µm-diameter hole was drilled. No Lenz-lens gasket was used. Instead, a platinum foil was placedon the culet surface to serve as a microwave antenna,without an electrical insulation layer.Continuous-wave (CW) ODMR was performed using acustom-built optical setup. As shown in Fig. 1c, a 532 nmgreen laser (MLL-S-532B, CNI laser) was used to irradi-ate the MDs to excite the NV center through an objectivelens (M Plan Apo SL 20x, Mitsutoyo). Red fluorescencecollected through the objective lens was passed through along-pass filter and detected by an avalanche photodiode(APD130A2, Thorlabs) coupled to a data acquisition de-vice (NI6363, National Instruments). Microwaves weregenerated using a signal generator (N5171B, Keysightor SynthHD, Windfreak) and amplified using a poweramplifier (ZHL-50W-63+, Mini-circuits). In wide-fieldODMR measurements, we used EMCCD camera (ixonUltra, Andor). ODMR measurements were conducted atroom temperature, and each ODMR spectrum was ac-quired within up to 10 minutes for both the APD-basedand EMCCD-based measurements.The NPD shows a broad peak in the photolumines-cence (PL) spectra between 600 and 800 nm, which maybe related to the presence of defects, dislocations, andgrain boundaries [26, 27]. Therefore, the signal detectedusing the avalanche photodiode includes a backgroundsignal derived from the NPD. Figure 1d shows the PLintensities of the anvil with an MD and the anvil alonefor both NPD and Type IIa SCD, where each dataset isnormalized to the PL intensity of the corresponding anvilwith MD configuration. The PL intensity from NPDa bdExcitedstates|±1>|0>MicrowavesBTPSingletstatesGroundstatesSampleNormalized PL intensity532 nm laserAPDorEMCCDcReGlycerolFIG. 1. (a) Energy diagram of NV center. A magneticfield B along the NV center splits the |±1⟩ states via Zee-man interaction. An isotoropic pressure P and temperatureT shifts the ZFS in the opposite directions. Anisotropic pres-sure splits the |±1⟩ states. (b) Setup of the nanopolycrys-talline diamond anvil cell. Light-blue region indicates thepressure-transmitting medium (glycerin) in the sample cham-ber formed by a rhenium gasket. The initial gasket thicknesswas 250 µm and was pre-indented to 50–60 µm; the sample-chamber hole diameter was 200–300 µm. The microdiamondsare placed on the culet surface. (c) Setup for the optical mea-surements. DM and LP denote dichroic mirror and long passfilter, respectively. (d) Normalized photoluminescence (PL)intensity of microdiamond (MD) on nanopolycrystalline dia-mond (NPD) and NPD itself, compared with Type IIa single-crystalline diamond. The vertical axis is normalized to thePL intensity of the MD on the corresponding anvil: for theNPD data, to the PL intensity of the MD on NPD; and forthe SCD data, to the PL intensity of the MD on SCD.was 4% of the MD, such that NPD did not affect theODMR experiments in our setup. On the other hand,background PL from NPD may become a limiting factorfor future applications that employ weaker emitters (e.g.,nanodiamonds and/or lower NV concentrations), wherethe signal-to-background ratio can decrease. For com-parison, the background signal from the Type IIa SCDalone was below the APD detection limit.CW ODMR was performed at increasing pressure (P0–P6) and decreasing pressure (P7–P10). Figure 2 showsthe CW ODMR spectra of the MD labeled NV1 at a laserpower of 5 mW. The vertical axis was normalized to thePL intensity at ambient pressure, labelled P0. At am-bient pressure, dips corresponding to the magnetic reso-nance were observed. The resonance peak split into two,which can arise from local strain and/or local electricfields associated with charged defects or impurities inthe MDs [37, 38]. By increasing the pressure, the res-onance peaks shifted toward higher frequencies, and thePL intensity decreased, as previously reported [17, 39].The ODMR spectra were recorded during the depressur-3ization process to ambient pressure. The PL intensityrecovered with decreasing pressure, whereas the PL in-tensity at P10 (after full pressure release) was approxi-mately 50% of that before applying the pressure. It isconsidered that the MDs moved when the pressure wasreleased, causing some of the fluorescence to be blockedby the cBN and TiO2 mixture.In P9, the difference between the two resonance peaksbecame larger than those in P7 and P8. This provides aplausible scenario in which P7/P8 reflect a broader dis-tribution of local strain environments within the MD,leading to spectral broadening. By contrast, in P9,stress/contact redistribution during decompression mayrender narrower local strain environments more domi-nant in the detected signal, allowing the splitting to beresolved more clearly. The ODMR lineshape in Fig. 2varies with pressure, which may reflect changes in re-laxation processes as well as inhomogeneous broadeningdue to local stress/strain. A more quantitative decompo-sition of these contributions using established zero-fieldODMR lineshape analysis methods is an important nextstep [40].P0P1P2P3P4P4P5P5P6P6P9P8P7P10NV1 Increasing pressureNV1 Decreasing pressureFIG. 2. CW ODMR spectra of the MD labeled NV1 underhigh pressure with (a) increasing pressure process and (b)decreasing pressure process. The vertical axes are normalizedby the PL intensity of the ambient pressure, labeled as P0.The black lines indicate fitting curves. The black arrows in(b) indicate the measurement order.The pressure was estimated from the value of the reso-nance frequency D under high pressure, using PODMR =(D −D0)/β GPa, where D0 = 2.87 GHz and β = 14.58MHz/GPa [17]. Figure 3 shows the ODMR pressures foreach measurement. We successfully performed ODMRabove 20 GPa. Because the ODMR contrast is approx-imately 8% even at 20 GPa, it is possible to performODMR even at high temperatures where the PL inten-sity and contrast decrease [12].FIG. 3. Pressure estimated from ODMR at each mea-surement sequence. Pressures are estimated using PODMR =(D−D0)/β GPa, where D0 = 2.87× 109 Hz, β = 14.58× 106GPa/Hz, and D denotes resonance frequency [17]. The errorbar represents a 95% confidence interval of the fitted value ofD.In high-pressure experiments using a DAC, a pres-sure distribution is expected, especially when the pres-sure medium is a solid or becomes solid under pressure.Because MDs can be dispersed throughout the samplespace, both the local pressure and the magnetic field canbe detected, providing beneficial insights into materialsunder high pressure [3, 20, 22]. Here, we demonstrate theODMR of three MDs, NV1, NV2, and NV3. NV1 is thesame as that used in Figs 2 and 3. Figure 4 shows theODMR results for the MDs and their positions. The res-onance frequencies and pressure estimated from ODMRwere 3.175±0.005 GHz and 20.9±0.3 GPa, 3.127±0.004GHz and 17.6 ± 0.3 GPa, and 3.130 ± 0.002 GHz and17.8± 0.1 GPa for NV1, NV2, and NV3, respectively.In addition to pressure manometry, the present plat-form may provide a route toward magnetic sensing underhigh pressure. To demonstrate feasibility under a biasfield, we acquired ODMR spectra under an externallyapplied magnetic field. Figure 4(b) shows the ODMRspectra of NV1 at P8 under the applied magnetic field.The bias magnetic field was applied by a permanent mag-net. The ODMR spectra showed clear field-dependentspectral changes even in the NPD-anvil configuration.This result supports the applicability of the platform tomagnetic measurements in high-pressure environments,as also suggested by prior demonstrations of magneticsensing using NV centers hosted in diamond particles un-der pressure [3].We also performed wide-field ODMR measurements,4NV1abNV1P8Zero bias fieldUnder bias fieldNV2NV3P6FIG. 4. (a) CW ODMR spectra on three MDs with NVcenter, termed as NV1, NV2, and NV3, respectively. Theresults of P6 are presented in this section. NV1 is the sameas that used in Figs 2 and 3. These spectra have offsets of−0.05 for NV2 and −0.1 for NV3, respectively. The insetshows the position of each MD in the sample space. (b) CWODMR spectra on NV1 at pressure sequence of P8 with nobias field and finite bias field. The spectrum obtained underfinite bias field has offsets of −0.08.which is a standard technique for simultaneously observ-ing the entire sample chamber in a single shot. FiveMDs, labeled NV4 to NV8, were enclosed within the sam-ple chamber. Figure 5(a) shows a fluorescence image ofthe MDs captured by the EMCCD camera. Figure 5(b)presents the ODMR spectra obtained under high pres-sure. The plotted ODMR data represents the signal in-tensity of a pixel for each respective microdiamond. Theresonance frequencies of the microdiamonds ranged from3.28 GHz to 3.39 GHz. These values correspond to pres-sures between 28 GPa and 35 GPa.Pressures inferred from different MDs can differ bymore than 10%. Such a spread is naturally expectedunder quasi-hydrostatic conditions once the pressure-transmitting medium solidifies, as spatial pressure inho-mogeneity and deviatoric stress develop across the sam-ple chamber. Indeed, Klotz et al. quantified pressuregradients by distributing multiple ruby spheres and ana-lyzing the standard deviation of ruby-derived pressures,reporting, for example, a standard deviation of ∼2 GPaat ∼20 GPa for a methanol–ethanol–water mixture [41].Accordingly, pressures obtained from individual MDsshould be interpreted as local effective pressures ratherthan a single uniform chamber pressure. In future stud-ies, simultaneous ruby fluorescence measurements wouldprovide a useful independent cross-check of the pressurescale and its spatial distribution.ab NV4NV5NV6NV7NV8NV4NV5NV6NV710 μmNV8FIG. 5. (a) Fluorescence image of the MDs captured bythe EMCCD camera. (b) CW ODMR spectra under highpressure. The spectra are offset by 0.02 each for clarity.The formation of the NV center and manipulation ofits spin state in NPD remain challenging. Although aPL peak near 637 nm has been observed in the as-grownNPD at 5 K, suggesting the natural presence of nega-tively charged NV centers, the formation and stabilityof these centers at room temperature remain uncertain[27]. NPD contains approximately 100 ppm of nitrogen,whereas the P1 center concentration is below 1 ppm [26].It is of interest to investigate whether NV centers can beintroduced and stabilized in NPD via ion implantationor chemical vapor deposition methods, as demonstratedin SCDs [42].A key practical advantage of NPD anvils is that theycan generate high pressures while maintaining relativelylarge culet sizes, which generally translates into a largeravailable sample chamber volume [29]. In the presentexperiments, we used a 0.6 mm culet, and previous stud-ies have reported that millimeter-class culets can stillreach pressures up to ∼80 GPa [30]. A larger acces-sible volume is advantageous for (i) the simultaneousmeasurement of multiple samples within a single load-ing and (ii) future integration with probes that benefitfrom larger sample volumes, such as neutron scattering.Importantly, achieving ODMR in an NPD–DAC is notguaranteed a priori because NPD can introduce addi-tional scattering and background luminescence that maydegrade the ODMR contrast. Therefore, our results pro-vide a practical foundation for extending NV-based sens-ing to extreme-pressure experiments, where larger samplevolumes and multi-sample throughput are desirable.The manipulation of the NV center under the concur-5rent application of high pressure and high temperaturepresents a compelling area of study because the NV cen-ter is known to function at high temperatures of 1400 K[43, 44] or high pressures of up to 100 GPa [5, 39, 45].Owing to the exceptionally high thermal conductivity ofSCD, maintaining a higher temperature within the sam-ple chamber presents significant challenges. In contrast,NPD exhibits lower thermal conductivity, thereby facili-tating the retention of higher temperatures [31]. Conse-quently, NPD is advantageous for conducting magneticresearch under extreme conditions of high pressure andhigh temperature. On the other hand, ODMR contrastdecreases substantially at elevated temperatures and un-der non-hydrostatic stress, and the resulting resonancebroadening/splitting can hinder quantitative analysis.Accordingly, performing ODMR-based NV sensing cen-ter under such conditions remains challenging. Employ-ing hydrostatic loading with a fluid pressure-transmittingmedium would help mitigate deviatoric stress and im-prove the reliability of magnetic sensing.While the present results support the feasibility ofODMR-based sensing in the NPD-DAC geometry, ex-tending the platform to quantitative magnetic-field imag-ing requires additional considerations when using MDs.Magnetic-field imaging using randomly oriented micro-/nano-diamond sensors has been reported under ambientconditions [46, 47], indicating that imaging is feasible inprinciple even without a predefined crystal orientation.In our experiments, individual MDs are generally placedwith orientations that are random with respect to theapplied bias field. Under a bias field, this leads to MD-dependent ODMR spectral patterns because multiple NVorientations contribute distinct resonances that can par-tially overlap, reducing practical resolvability and com-plicating quantitative fitting. Furthermore, under DACconditions, non-hydrostatic stress can induce additionalresonance broadening and/or splitting of the resonancesand reduce the ODMR contrast, making quantitativeanalysis even more challenging. Therefore, more quan-titative magnetic imaging in future work would benefitfrom hydrostatic pressure conditions using a gas pressure-transmitting medium and/or sensor geometries with awell-defined orientation, for example, by employing anSCD sensor chip inserted into the sample chamber, asadopted in previous studies [48].Recently, some authors have developed an electricaltransport measurement system under high pressure, us-ing boron-doped diamond (BDD) as electrodes [49–51].Additionally, they have engineered a heating system forhigh-pressure environments employing BDD as a resis-tance heater and a thermometer [52–54]. BDD can besynthesized on NPD through microwave plasma chemi-cal vapor deposition, a process similar to that used forSCD. The integration of BDD electrodes, BDD heaters,and MDs with NV centers facilitates the simultaneousmeasurement of electrical resistance and magnetic fieldsunder conditions of elevated temperature and pressure.Very recently, we have demonstrated coherent control ofNV spins using a BDD circuit as a microwave antenna,which could work under high pressure and temperature[55]. The BDD electrode is highly durable and can bereused multiple times until the diamond itself breaks, re-ducing experimental preparation time and subsequentlyfacilitating the investigation of physical properties underhigh-temperature and high-pressure conditions.In conclusion, we demonstrated continuous-wave opti-cally detected magnetic resonance of nitrogen vacancycenters in microdiamonds inside a diamond anvil cellpressurized with nanopolycrystalline diamonds as theanvil. We observed magnetic resonance on nitrogen va-cancy centers under conditions where the nitrogen va-cancy centers in microdiamonds served as markers forpressures exceeding 30 GPa. Furthermore, we observedcontinuous-wave optically detected magnetic resonancein three independent microdiamonds within the samplespace, where the resonance frequency of the NV centervaried with the pressure distribution. The combination ofnanopolycrystalline diamonds and microdiamonds con-taining NV centers is up-and-coming for pressure andmagnetic sensing under concurrent high pressure andtemperature.ACKNOWLEDGMENTSThis work was supported by JSPS KAKENHI Grantnumbers JP24KJ1035, JP23K26528, JP23KK0267. Thiswork was also supported by the Joint Usage/ResearchCenter PRIUS, Ehime University, Japan. M.O. receivesfunding from JSPS Grant-in-Aid for JSPS Fellows Grantnumber JP24KJ1035.[1] S. Hsieh, P. Bhattacharyya, C. Zu, T. Mittiga, T. J.Smart, F. Machado, B. Kobrin, T. O. Höhn, N. Z. Rui,M. Kamrani, S. 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