Publisher：IOP Publishing  

Abstract

A nitrogen-vacancy (NV) center in a diamond enables the access to an electron spin, which is expected to present highly sensitive quantum sensors. Although exploiting a nitrogen nuclear spin improves the sensitivity, manipulating it using a resonant pulse requires a long gate time owing to its small gyromagnetic ratio. Another technique to control nuclear spins is a conditional rotation gate based on dynamical decoupling, which is faster but unavailable for nitrogen spins owing to the lack of transverse hyperfine coupling with the electron spin. In this study, we generated effective transverse coupling by applying a weak off-axis magnetic field. An effective coupling depends on the off-axis field; the conditional rotation gate on the nitrogen-14 spins of an NV center was demonstrated within 4.2 μs under an 1.8% off-axis field and a longitudinal field of approximately 280 mT. We estimated that a population transfer from the electron to nitrogen spins can be implemented with 8.7 μs. Our method is applicable to an ensemble of NV centers, in addition to a single NV center.

DOI： 10.1088/2399-6528/ad2b8b

arXiv

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Other Link： https://iopscience.iop.org/article/10.1088/2399-6528/ad2b8b/pdf

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

Chern numbers characterize topological phases in a wide array of physical systems. However, the resilience of system topology to external perturbations makes it challenging experimentally to investigate transitions between different phases. In this study, we demonstrate the transitions of a Chern number from 0 to 3, synthesized in an electronic-nuclear spin system associated with the nitrogen-vacancy (NV) centre in diamond. The Chern number is characterized by the number of degeneracies enclosed in a control Hamiltonian parameter sphere. Topological transitions between different phases are realized by varying the radius and offset of the sphere such that the Chern number changes. We show that the measured topological phase diagram is consistent with numerical calculations and can also be mapped onto an interacting three-qubit system. The NV system may also allow access to even higher Chern numbers, which could be applied to exploring exotic topology or topological quantum information.

DOI： 10.1038/s41534-023-00732-6

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Other Link： https://www.nature.com/articles/s41534-023-00732-6

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/physrevapplied.19.044089

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Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevApplied.19.044089/fulltext

Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

Accurate prediction of the remaining driving range of electric vehicles is difficult because the state-of-the-art sensors for measuring battery current are not accurate enough to estimate the state of charge. This is because the battery current of EVs can reach a maximum of several hundred amperes while the average current is only approximately 10 A, and ordinary sensors do not have an accuracy of several tens of milliamperes while maintaining a dynamic range of several hundred amperes. Therefore, the state of charge has to be estimated with an ambiguity of approximately 10%, which makes the battery usage inefficient. This study resolves this limitation by developing a diamond quantum sensor with an inherently wide dynamic range and high sensitivity for measuring the battery current. The design uses the differential detection of two sensors to eliminate in-vehicle common-mode environmental noise, and a mixed analog–digital control to trace the magnetic resonance microwave frequencies of the quantum sensor without deviation over a wide dynamic range. The prototype battery monitor was fabricated and tested. The battery module current was measured up to 130 A covering WLTC driving pattern, and the accuracy of the current sensor to estimate battery state of charge was analyzed to be 10 mA, which will lead to 0.2% CO₂ reduction emitted in the 2030 WW transportation field. Moreover, an operating temperature range of − 40 to + 85 °C and a maximum current dynamic range of ± 1000 A were confirmed.

DOI： 10.1038/s41598-022-18106-x

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Other Link： https://www.nature.com/articles/s41598-022-18106-x

Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

Magnetocardiography is a contactless imaging modality for electric current propagation in the cardiovascular system. Although conventional sensors provide sufficiently high sensitivity, their spatial resolution is limited to a centimetre-scale, which is inadequate for revealing the intra-cardiac electrodynamics such as rotational waves associated with ventricular arrhythmias. Here, we demonstrate invasive magnetocardiography of living rats at a millimetre-scale using a quantum sensor based on nitrogen-vacancy centres in diamond. The acquired magnetic images indicate that the cardiac signal source is well explained by vertically distributed current dipoles, pointing from the right atrium base via the Purkinje fibre bundle to the left ventricular apex. We also find that this observation is consistent with and complementary to an alternative picture of electric current density distribution calculated with a stream function method. Our technique will enable the study of the origin and progression of various cardiac arrhythmias, including flutter, fibrillation, and tachycardia.

DOI： 10.1038/s42005-022-00978-0

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Other Link： https://www.nature.com/articles/s42005-022-00978-0

Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

DOI： 10.1063/5.0031502

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Authorship：Lead author   Language：English   Publisher：NATURE PUBLISHING GROUP  

The nitrogen vacancy centre in diamond is a leading platform for nanoscale sensing and imaging, as well as quantum information processing in the solid state. To date, individual control of two nitrogen vacancy electronic spins at the nanoscale has been demonstrated. However, a key challenge is to scale up such control to arrays of nitrogen vacancy spins. Here, we apply nanoscale magnetic resonance frequency encoding to realize site-selective addressing and coherent control of a four-site array of nitrogen vacancy spins. Sites in the array are separated by 100 nm, with each site containing multiple nitrogen vacancies separated by similar to 15 nm. Microcoils fabricated on the diamond chip provide electrically tuneable magnetic field gradients similar to 0.1 G/nm. Tailored application of gradient fields and resonant microwaves allow site-selective nitrogen vacancy spin manipulation and sensing applications, including Rabi oscillations, imaging, and nuclear magnetic resonance spectroscopy with nanoscale resolution. Microcoil-based magnetic resonance of solid-state spins provides a practical platform for quantum-assisted sensing, quantum information processing, and the study of nanoscale spin networks.

DOI： 10.1038/s41534-017-0033-3

arXiv

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Authorship：Lead author  

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.bpj.2013.11.1133

Web of Science

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Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/physrevlett.110.157601

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Other Link： http://link.aps.org/article/10.1103/PhysRevLett.110.157601

Language：English  

DOI： 10.1016/j.bpj.2012.11.1088

Web of Science

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Language：Japanese   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

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Language：Japanese   Presentation type：Symposium, workshop panel (nominated)  

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Language：English   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

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