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.

Magnetic field imaging of magnetic particles using diamond sensors with nitrogen-vacancy (NV) centers has the potential to become a new prominent living-cell observation method, because of the reduction of photodamage to cells. To realize a higher signal-to-noise ratio of magnetic detection, perfectly aligned and high-density NV centers in the diamond are required because they are effective in reducing optical shot noise. In this study, diamond films were grown by microwave plasma CVD on (111) substrates. The highest NV density with a perfectly aligned NV axis of 7 × 10 17 cm −3 was obtained with a high growth rate due to the increase of vacancies, and the reduction of the optical shot noise to 1/4 was confirmed. Moreover, magnetic field imaging with different-thickness NVs in CVD-grown diamonds showed the dependence of the magnetic field distribution pattern and SNR on the diamond film thickness.

Energy conservation and battery life extension are key challenges for the next-generation hybrid electric vehicles. In particular, the temperature and electric currents in a storage battery need to be monitored simultaneously with ∼1 kHz signal bandwidth for optimum battery usage. Here we introduce a centimeter-scale portable quantum sensor head, consisting of a diamond substrate hosting an ensemble of nitrogen-vacancy (NV) color centers with a density of ∼3 × 1017 cm−3. One diamond surface is attached to a multi-mode fiber for simultaneous optical excitation and readout of the NV centers, while the other diamond surface is attached to a coplanar microwave guide for NV spin ground-state mixing. Signal bandwidth of 1 kHz was realized through time-domain multiplexing of the two-tone microwave frequency modulation at 20 kHz. Two microwave frequencies were locked to the two resonance points that were determined from the optically detected magnetic resonance spectrum. From the mean and the difference of the deviation from the two locked frequencies, the temperature and magnetic field were obtained simultaneously and independently, with sensitivities of 3.5 nT/Hz1/2 and 1.3 mK/Hz1/2, respectively. We also showed that our sensor reached a minimum detectable magnetic field of 5 pT by accumulating signals for over 10 000 s.

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.

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Ultimate sensitivity for quantum magnetometry using nitrogen-vacancy (NV) centers in diamond is limited by number of NV centers and coherence time. Microwave irradiation with a high and homogeneous power density for a large detection volume is necessary to achieve highly sensitive magnetometer. Here, we demonstrate a microwave resonator to enhance the power density of the microwave field and an optical system with a detection volume of 1.4×10 −3 mm 3 . The strong microwave field enables us to achieve 48 ns Rabi oscillation which is sufficiently faster than the phase relaxation time of NV centers. This system combined with a decoupling pulse sequence, XY16, extends the spin coherence time (T2) up to 27 times longer than that with a spin echo method. Consequently, we obtained an AC magnetic field sensitivity of 10.8 pt/√Hz using the dynamical decoupling pulse sequence. Ensemble nitrogen-vacancy (NV) centers in diamond are expected to reach a magnetic sensitivity in the femto-tesla range at room temperature, required for biological/medical applications including magnetoencephalography [1-4]. The sensitivity of diamond magnetometer is determined by number of the NV centers, spin coherence time, and detection efficiency [5, 6]. Pioneering work reported by Wolf et al. achieved the highest AC magnetic field sensitivity of 900 fT/√Hz by enlarging the detection volume to increase the number of the NV centers used for detection. Wolf et al. achieved a detection volume of 8.5× 10 −4 mm 3 , a high detection efficiency of 65 %, and a spin coherence time of 100s obtained by a spin echo sequence [7].Dynamical decoupling of the large detection volume for extension of the spin coherence time beyond spin echo limit is necessary to extend its sensitivity limit. As for a single NV center, the dynamical decoupling sequences have been utilized to improve the spin coherence time and thus a magnetic sensitivity [8]. For driving the large volume of the NV ensembles, spatial inhomogeneity of the microwave field creates different Rabi oscillations of each NV center, causing rapid decays of the average signal from the NV ensemble. Therefore, the spatial homogeneity of the microwave field in the decoupling sequence becomes important. Furthermore, the Rabi oscillation faster than phase coherence time T2* is critical to reduce the control error of the dynamical decoupling pulses. Thus, uniform and strong microwave driving is essential to achieve the dynamical decoupling for the large detection volume. In previous reports, the microwave irradiation of the large detection volume of the ensemble NV centers was performed by means of a spin echo sequence only [7,9].In this study, we constructed an efficient microwave and optical system and applied dynamical decoupling pulse sequences to an ensemble of NV centers in a large detection volume of 1.4×10 −3 mm 3 . We used a coplanar waveguide resonator (CWR) with a wide center electrode for strong and uniform microwave irradiation. CWR enhances the microwave field only at the targeted frequency bandwid...

The spatial and temporal resolutions of bio‐imaging with magnetic nanoparticles (MNP) as a label and a diamond substrate as a magnetic field imager are investigated. To realize fast and accurate magnetic field imaging even for a substrate with unresolved hyperfine peaks, relative fluorescence is measured at four operation points corresponding to the steepest slopes of two dips in the ODMR spectrum. The (111) diamond substrate with a 3.5‐μm thick chemical vapor deposition film with an NV− density of 1.6 × 1016 cm−3 allows us to detect 1‐μm MNPs scattered on its surface with an accumulated exposure time of 19 s under external DC magnetic field of 1.3 mT. Theoretical limit of temporal sensitivity is estimated to be more than four orders of magnitude smaller than measured. Although for measurement in culture medium, an objective lens with longer working distance is required and the condition will become somewhat worse, a spatiotemporal resolution of <1 s and <1 μm for the density and quality of the NV centers used in this study is expected if the already reported sensitivity enhancement technologies are further incorporated.

A 1 -GHz -clock Josephyon microcomputer system has been developed to demonstrate the possibility of a high-speed superconducting computer system. It consists of a 4b data processor chip and a 1 Kb RAM chip. For the fabrication of these Josephson integrated circuits, a cross -shaped Nb / AlOx / Nb Josephson junction process has been developed to realize small junction size and improve critical current uniformity, and has made fabrication of LSIs with several thousand gates possible. A latch -up-free DC flip-flop is an important element in the high-speed Josephson logic and memory circuits, having been newly applied to an all -DC -powered Josephson RAM with asynchronous access capabi 1 i ty.