Nobu-Hisa Kaneko

The EU regulation presents several indicators to measure battery residual value, to reduce the environmental impact of battery manufacturing. IEC62620 has been identified as the standard to measure internal resistance, one of the defined indicators. While it describes a method for measuring AC internal resistance at 1 kHz, there are no reports of on-board measurement methods that can be directly incorporated into battery packs. This study proposes a new method for measuring the frequency dependence of the internal impedance of storage batteries and quantitatively validates for compliance with the International Electrotechnical Commission (IEC) standards and Japanese Industrial Standards (JIS). The proposed method utilizes the charging power of a storage battery to discharge it in the form of a square waveform. The frequency dependence of the impedance is determined through an active frequency sweep controlled by the Integrated Circuit (IC) developed in this work. High-precision measurements confirm that the proposed method complies with the IEC62620 standard for measuring the resistance component at 1000 Hz. Furthermore, it exhibits strong agreement with conventional methods within the estimated uncertainties in the 500 Hz – 2000 Hz frequency range. The proposed method is novel in that it employs square-wave discharge currents to evaluate the performance and reliability of storage batteries in accordance with IEC and corresponding JIS standards. This new method enables simpler and more compact systems that can be installed on-board, as opposed to conventional impedance measurements using sine waves. The proposed method has potential applications in reuse and recycling systems for storage batteries.

Planar multijunction thermal converters (MJTCs) have been used as standards in AC voltage measurements. Consequently, predicting the long-term stability is crucial. Here, we present a statistically supported, highly accelerated lifetime test (HALT) for planar MJTCs. The HALT employs elevated temperatures to rapidly degrade the performance of bismuth-antimony-copper thermocouples while preserving the original failure mode. Based on Weibull–Arrhenius modeling at multiple temperatures, the predicted lifetime of the current MJTC design exceeds 20 years, whereas the previous version had a lifetime of only 45 days. This estimate is consistent with more than 10 years of non-accelerated monitoring, reinforcing the validity of the acceleration model. The use of elevated temperatures enabled a tenfold reduction in testing time. The significant difference in predicted lifetime between the two designs is mainly attributed to an increased scale parameter β, reflecting improved stability at the thermocouple interface. These findings highlight the effectiveness of HALT for rapid and reliable prediction of MJTC lifetime during the early-stage device development.

Coherent manipulation of plasmon wavepackets in solid-state systems is crucial for advancing nanoscale electronic devices, offering a unique platform for quantum information processing based on propagating quantum bits. Controlling the eigenstate of plasmon wavepackets is essential, as it determines their propagation speed and hence the number of quantum operations that can be performed during their flight time through a quantum system. When plasmon wavepackets are generated by short voltage pulses and transmitted through nanoscale devices, they distribute among multiple electron conduction channels via Coulomb interactions, a phenomenon known as charge fractionalisation. This spreading complicates plasmon manipulation in quantum circuits and makes precise control of the eigenstates of plasmon wavepackets challenging. Using a cavity, we demonstrate the ability to isolate and select electron conduction channels contributing to plasmon excitation, thus enabling precise control of plasmon eigenstates. Specifically, we observe an electron-channel blockade effect, where charge fractionalisation into cavity-confined channels is suppressed due to the plasmon’s narrow energy distribution, enabling more stable and predictable plasmonic circuits. This technique provides a versatile tool for designing plasmonic circuits, offering the ability to tailor plasmon speed through local parameters, minimise unwanted plasmon excitation in adjacent circuits, and enable the precise selection of electron-channel plasmon eigenstates in quantum interferometers.

The development of an ultra-compact Zener-voltage-standard module intended as a detachable and replaceable DC voltage reference to ensure traceability in measurement instruments is currently in progress. To date, several prototypes of this detachable Zener module have been designed, assembled, and tested. This paper presents an evaluation of the output voltage stability of these prototypes under changes in ambient temperature, pressure, humidity, and over time. The latest prototype demonstrates a drift rate, temperature coefficient, pressure coefficient, and humidity coefficient within 1 μV/V per year, 0.01 (μV/V)/°C, 0.2 (nV/V)/hPa, and 0.2 μV/V, respectively.

The operation of superconducting qubits requires a sensitive readout circuit at cryogenic temperatures, driving the demand for cryogenic non-reciprocal microwave components such as circulators. However, evaluating these components at low temperatures presents significant challenges for companies and institutions without specialized measurement systems. In the development of such cryogenic non-reciprocal components, the temperature dependence of ferrite’s magnetic properties is the most critical factor. Therefore, an evaluation technique for accurately assessing these properties at cryogenic temperatures is essential. In this study, we develop a measurement method to characterize low-loss ferrite materials over a temperature range of 300 K to 2 K. The use of the circularly polarized resonance mode TE_11n enables the direct estimation of circular complex permeability and the determination of key material parameters, including saturation magnetization and damping constant—both essential for assessing the performance of ferrite materials in circulator applications. To validate the reliability of our measurement method, we selected single-crystal YIG as the test material, as its magnetic properties at cryogenic temperatures are relatively well known. This demonstration confirms that our method is effective for characterizing various low-loss ferrite materials that are potential candidates for compact cryogenic non-reciprocal devices.

Surface acoustic wave (SAW) technology has been explored in thin-film materials to discover fundamental phenomena and to investigate their physical properties. It is used to excite and manipulate quasiparticles such as phonons or magnons and can dynamically modulate the properties of the materials. In the field, SAWs are typically excited by a continuous wave at a resonant frequency. Recently, generation of a single-cycle SAW pulse has been demonstrated on GaAs substrate. Such a SAW pulse provides a potential to access a single quasiparticle excitation and to investigate its dynamics by time-resolved measurements. On the other hand, to modulate and control the properties of thin-film materials, it is generally required to generate high-intensity SAWs. In this work, we demonstrate the efficient generation of a SAW pulse using a chirp interdigital transducer (IDT) on LiNbO3 substrate. We have fabricated chirp IDT devices with bandwidths from 0.5 GHz to 5.5 GHz. We also confirmed the generation of a SAW pulse with 0.3 ns full width at half maximum by performing time-resolved measurements. The conversion efficiency between input power and SAW on LiNbO3 substrate is approximately 45 times larger than that on GaAs substrate. This enables us to generate a high-intensity SAW pulse, meeting the requirement for the modulation of thin films. Our results will expand the research in the field, such as spintronics and magnonics, and lead to their further advancements.

Electronic flying qubits offer an interesting alternative to photonic qubits: electrons propagate slower, hence easier to control in real time, and Coulomb interaction enables direct entanglement between different qubits. Although their coherence time is limited, flying electrons in the form of picosecond plasmonic pulses could be competitive in terms of the number of achievable coherent operations. The key challenge in achieving this critical milestone is the development of a new technology capable of injecting ‘on-demand’ single-electron wavepackets into quantum devices, with temporal durations comparable to or shorter than the device dimensions. Here, we take a significant step towards achieving this regime in a quantum nanoelectronic system by injecting ultrashort single-electron plasmonic pulses into a 14-micrometer-long Mach-Zehnder interferometer. Our results establish that quantum coherence is robust under the on-demand injection of ultrashort plasmonic pulses, as evidenced by the observation of coherent oscillations in the single-electron regime. Building on this, our results demonstrate the existence of a “non-adiabatic" regime that is prominent at high frequencies. This result highlights the potential of flying qubits as a promising alternative to localised qubit architectures, offering advantages such as a reduced hardware footprint, enhanced connectivity, and scalability for quantum information processing.

This paper reports on a numerical simulation using the finite-element method (FEM) on the effects of shielding and guarding electrodes of a vacuum-gap capacitor using coaxial cylindrical electrodes on the capacitance gradient measurements for an electrostatic force balance apparatus. The electric field of the coaxial cylindrical capacitor with a shielding electrode was computed when the capacitor was open or semi-closed using a grounded-guarding electrode placed around the positive-terminal electrode. The capacitance and unwanted capacitive coefficients between the positive-terminal and grounded electrodes were calculated using the computed electric fields. The FEM results suggested that, under given conditions, there is an optimal overlapping length in the longitudinal direction of the coaxial cylindrical electrodes of the capacitor. This is based on the linearity of the capacitance gradient and parasitic capacitances that resulted in an error in the determination of the capacitance gradient using a three-terminal capacitance bridge in the electrostatic force balance measurement. The FEM simulations also suggested that the use of a guarding electrode reduced the unwanted parasitic capacitive coefficients between the terminal and shielding electrodes, whereas the guarding electrode had no significant impact on the linearity of the capacitance gradient. Experiments were also conducted to confirm the consistency of the FEM results, which showed good agreement within the measurement uncertainties.

Ultrastable metal foil 10 kΩ standard resistors are developed. The resistors showed quite stable behavior and the observed long-term resistance drift was around ±10 nΩ/Ω in 2 years from just after the fabrication. They showed almost linear temperature characteristics from 18 ◦C to 28 ◦C and the temperature coefficients were less than 15 (nΩ/Ω)/K at around 23 ◦C. Due to their stress-free structure, the resistance values were quite stable within 5 nΩ/Ω after the abrupt temperature change of about 5 ◦C. The humidity dependence was within ±0.2 (nΩ/Ω)/% at 23 ◦C and they also showed stable behavior within ±10 nΩ/Ω against the pressure from 700 hPa to 1200 hPa. A vibration test along with a MIL standard, MIL-STD-202, was performed, and a 2.5 kΩ subsection of the 10 kΩ resistor indicated stability within 10 nΩ/Ω after applying vibration for 2 hours on each axis (6 hours in total).