{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,2]],"date-time":"2026-10-02T20:57:15Z","timestamp":1790974635153,"version":"4.1.0"},"reference-count":32,"publisher":"MDPI AG","issue":"3","license":[{"start":{"date-parts":[[2021,2,2]],"date-time":"2021-02-02T00:00:00Z","timestamp":1612224000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100001700","name":"Ministry of Education, Culture, Sports, Science and Technology","doi-asserted-by":"publisher","award":["JPMXS0118067395"],"award-info":[{"award-number":["JPMXS0118067395"]}],"id":[{"id":"10.13039\/501100001700","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001691","name":"Japan Society for the Promotion of Science","doi-asserted-by":"publisher","award":["KAKENHI (20K14392)"],"award-info":[{"award-number":["KAKENHI (20K14392)"]}],"id":[{"id":"10.13039\/501100001691","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>The negatively charged nitrogen-vacancy (NV) center in diamonds is known as the spin defect and using its electron spin, magnetometry can be realized even at room temperature with extremely high sensitivity as well as a high dynamic range. However, a magnetically shielded enclosure is usually required to sense weak magnetic fields because environmental magnetic field noises can disturb high sensitivity measurements. Here, we fabricated a gradiometer with variable sensor length that works at room temperature using a pair of diamond samples containing negatively charged NV centers. Each diamond is attached to an optical fiber to enable free sensor placement. Without any magnetically shielding, our gradiometer realizes a magnetic noise spectrum comparable to that of a three-layer magnetically shielded enclosure, reducing the noises at the low-frequency range below 1 Hz as well as at the frequency of 50 Hz (power line frequency) and its harmonics. These results indicate the potential of highly sensitive magnetic sensing by the gradiometer using the NV center for applications in noisy environments such as outdoor and in vehicles.<\/jats:p>","DOI":"10.3390\/s21030977","type":"journal-article","created":{"date-parts":[[2021,2,2]],"date-time":"2021-02-02T05:44:42Z","timestamp":1612244682000},"page":"977","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":20,"title":["Gradiometer Using Separated Diamond Quantum Magnetometers"],"prefix":"10.3390","volume":"21","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-1733-095X","authenticated-orcid":false,"given":"Yuta","family":"Masuyama","sequence":"first","affiliation":[{"name":"Takasaki Advanced Radiation Research Institute, National Institutes for Quantum and Radiological Science and Technology, Takasaki, Gunma 370-1292, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Katsumi","family":"Suzuki","sequence":"additional","affiliation":[{"name":"Department of Electrical and Electronic Engineering, Tokyo Institute of Technology, Meguro, Tokyo 152-8552, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Akira","family":"Hekizono","sequence":"additional","affiliation":[{"name":"Department of Civil and Environmental Engineering, Tokyo Institute of Technology, Meguro, Tokyo 152-8552, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mitsuyasu","family":"Iwanami","sequence":"additional","affiliation":[{"name":"Department of Civil and Environmental Engineering, Tokyo Institute of Technology, Meguro, Tokyo 152-8552, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mutsuko","family":"Hatano","sequence":"additional","affiliation":[{"name":"Takasaki Advanced Radiation Research Institute, National Institutes for Quantum and Radiological Science and Technology, Takasaki, Gunma 370-1292, Japan"},{"name":"Department of Electrical and Electronic Engineering, Tokyo Institute of Technology, Meguro, Tokyo 152-8552, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Takayuki","family":"Iwasaki","sequence":"additional","affiliation":[{"name":"Department of Electrical and Electronic Engineering, Tokyo Institute of Technology, Meguro, Tokyo 152-8552, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7850-3164","authenticated-orcid":false,"given":"Takeshi","family":"Ohshima","sequence":"additional","affiliation":[{"name":"Takasaki Advanced Radiation Research Institute, National Institutes for Quantum and Radiological Science and Technology, Takasaki, Gunma 370-1292, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2021,2,2]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"810","DOI":"10.1038\/nphys1075","article-title":"High-Sensitivity Diamond Magnetometer with Nanoscale Resolution","volume":"4","author":"Taylor","year":"2008","journal-title":"Nat. Phys."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1016\/j.physrep.2013.02.001","article-title":"The Nitrogen-Vacancy Colour Centre in Diamond","volume":"528","author":"Doherty","year":"2013","journal-title":"Phys. Rep."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"83","DOI":"10.1146\/annurev-physchem-040513-103659","article-title":"Nitrogen-Vacancy Centers in Diamond: Nanoscale Sensors for Physics and Biology","volume":"65","author":"Schirhagl","year":"2014","journal-title":"Annu. Rev. Phys. Chem."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"063111","DOI":"10.1063\/1.4908528","article-title":"High-Frequency and High-Field Optically Detected Magnetic Resonance of Nitrogen-Vacancy Centers in Diamond","volume":"106","author":"Stepanov","year":"2015","journal-title":"Appl. Phys. Lett."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"047601","DOI":"10.1103\/PhysRevLett.112.047601","article-title":"Electronic Properties and Metrology Applications of the Diamond NV\u2212Center under Pressure","volume":"112","author":"Doherty","year":"2014","journal-title":"Phys. Rev. Lett."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"677","DOI":"10.1038\/nnano.2016.63","article-title":"Quantitative Nanoscale Vortex Imaging Using a Cryogenic Quantum Magnetometer","volume":"11","author":"Thiel","year":"2016","journal-title":"Nat. Nanotechnol."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"1355","DOI":"10.1126\/science.aaw4278","article-title":"Measuring Magnetic Field Texture in Correlated Electron Systems under Extreme Conditions","volume":"366","author":"Yip","year":"2019","journal-title":"Science"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"17604","DOI":"10.1021\/ja0567081","article-title":"Bright Fuorescent Nanodiamonds: No Photobleaching and Low CY-Totoxicity","volume":"127","author":"Yu","year":"2005","journal-title":"J. Am. Chem. Soc."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"5726","DOI":"10.1021\/nl302979d","article-title":"Real-Time Background-Free Selective Imaging Fluorescent Nanodiamonds in Vivo","volume":"12","author":"Igarashi","year":"2012","journal-title":"Nano Lett."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"400","DOI":"10.1021\/acs.accounts.5b00484","article-title":"Fluorescent Nanodiamond: A Versatile Tool for Long-Term Cell Tracking, Super-Resolution Imaging, and Nanoscale Temperature Sensing","volume":"49","author":"Hsiao","year":"2016","journal-title":"Accounts Chem. Res."},{"key":"ref_11","first-page":"E6730","article-title":"Optical Magnetic Detection of Single-Neuron Action Potentials Using Quantum Defects in Diamond","volume":"114","author":"Barry","year":"2017","journal-title":"Proc. Natl. Acad. Sci. USA"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"231103","DOI":"10.1063\/1.5095241","article-title":"Nanotesla Sensitivity Magnetic Field Sensing Using a Compact Diamond Nitrogen-Vacancy Magnetometer","volume":"114","author":"Webb","year":"2019","journal-title":"Appl. Phys. Lett."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"59","DOI":"10.1016\/j.diamond.2019.01.008","article-title":"Compact Integrated Magnetometer Based on Nitrogen-Vacancy Centres in Diamond","volume":"93","author":"Brenneis","year":"2019","journal-title":"Diam. Relat. Mater."},{"key":"ref_14","first-page":"041001","article-title":"Subpicotesla Diamond Magnetometry","volume":"5","author":"Wolf","year":"2015","journal-title":"Phys. Rev. X"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"023394","DOI":"10.1103\/PhysRevResearch.2.023394","article-title":"Diamond Magnetometer Enhanced by Ferrite Flux Concentrators","volume":"2","author":"Fescenko","year":"2020","journal-title":"Phys. Rev. Res."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"784","DOI":"10.1126\/science.161.3843.784","article-title":"Magnetoencephalography: Evidence of Magnetic Fields Produced by Alpha-Rhythm Currents","volume":"161","author":"Cohen","year":"1968","journal-title":"Science"},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"664","DOI":"10.1126\/science.175.4022.664","article-title":"Magnetoencephalography: Detection of the Brain\u2019s Electrical Activity with a Superconducting Magnetometer","volume":"175","author":"Cohen","year":"1972","journal-title":"Science"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"386","DOI":"10.1016\/j.neuroimage.2011.11.074","article-title":"Magnetoencephalography: From SQUIDs to Neuroscience: Neuroimage 20th Anniversary Special Edition","volume":"61","author":"Hari","year":"2012","journal-title":"NeuroImage"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"211104","DOI":"10.1063\/1.2392722","article-title":"Magnetoencephalography with an Atomic Magnetometer","volume":"89","author":"Xia","year":"2006","journal-title":"Appl. Phys. Lett."},{"key":"ref_20","first-page":"657","article-title":"Moving Magnetoencephalography Towards Real-World Applications with a Wearable System","volume":"555","author":"Boto","year":"2018","journal-title":"Nat. Cell Biol."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"702","DOI":"10.1063\/1.323659","article-title":"SQUID Instruments and Shielding for Low-Level Magnetic Measurements","volume":"48","author":"Zimmerman","year":"1977","journal-title":"J. Appl. Phys."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"260","DOI":"10.1109\/TMAG.1982.1061780","article-title":"Design, Construction, and Performance of a Large-Volume Magnetic Shield","volume":"18","author":"Pukki","year":"1982","journal-title":"IEEE Trans. Magn."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"R31","DOI":"10.1088\/0957-0233\/18\/3\/R01","article-title":"Induction Coil Sensors\u2014A Review","volume":"18","author":"Tumanski","year":"2007","journal-title":"Meas. Sci. Technol."},{"key":"ref_24","first-page":"325","article-title":"A Laser-Pumped Magnetometer for the Mapping of Human Cardiomagnetic Fields","volume":"76","author":"Bison","year":"2003","journal-title":"Appl. Phys. A"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"031106","DOI":"10.1063\/1.4974349","article-title":"A Microfabricated Optically-Pumped Magnetic Gradiometer","volume":"110","author":"Sheng","year":"2017","journal-title":"Appl. Phys. Lett."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"124519","DOI":"10.1063\/1.4771924","article-title":"Room-Temperature Operation of a Radiofrequency Diamond Magnetometer near the Shot-Noise Limit","volume":"112","author":"Shin","year":"2012","journal-title":"J. Appl. Phys."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"011112","DOI":"10.1063\/1.5024583","article-title":"Quantum Stereomagnetometry with a Dual-Core Photonic-Crystal Fiber","volume":"113","author":"Blakley","year":"2018","journal-title":"Appl. Phys. Lett."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"125007","DOI":"10.1063\/1.5047078","article-title":"Extending Coherence Time of Macro-Scale Diamond Magnetometer by Dynamical Decoupling with Coplanar Waveguide Resonator","volume":"89","author":"Masuyama","year":"2018","journal-title":"Rev. Sci. Instrum."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"714","DOI":"10.1016\/j.carbon.2018.11.051","article-title":"Increased Nitro-Gen-Vacancy Centre Creation Yield in Diamond through Electron Beam Irradiation at High Temperature","volume":"143","author":"Capelli","year":"2019","journal-title":"Carbon"},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"034044","DOI":"10.1103\/PhysRevApplied.10.034044","article-title":"Simultaneous Broadband Vector Magnetometry Using Solid-State Spins","volume":"10","author":"Schloss","year":"2018","journal-title":"Phys. Rev. Appl."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"252406","DOI":"10.1063\/1.5034216","article-title":"Robust High-Dynamic-Range Vector Magnetometry with Nitrogen-Vacancy Centers in Diamond","volume":"112","author":"Clevenson","year":"2018","journal-title":"Appl. Phys. Lett."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"101101","DOI":"10.1063\/1.2354545","article-title":"Superconducting Quantum Interference Device Instruments and Applications","volume":"77","author":"Fagaly","year":"2006","journal-title":"Rev. Sci. Instrum."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/21\/3\/977\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T05:18:34Z","timestamp":1760159914000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/21\/3\/977"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2021,2,2]]},"references-count":32,"journal-issue":{"issue":"3","published-online":{"date-parts":[[2021,2]]}},"alternative-id":["s21030977"],"URL":"https:\/\/doi.org\/10.3390\/s21030977","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2021,2,2]]}}}