量子コンピュータは次世代の情報処理技術として期待が高まっており,世界中で開発競争が激化している。量子コンピュータの基本構成要素である量子ビットは,ポテンシャル中に存在する最低エネルギーの二つの量子化準位を実効的な2準位系とみなして演算を行う。量子化された2準
Nowadays, quantum computers are attracting much interest. In current quantum computers, measurement instruments, which provide functions of controlling and reading out quantum bits (qubits), operate under room temperature, and the instruments and qubits are connected by cables. This means that many cables are required for large-scale quantum computers, which could cause scalability issue. To reduce such cables, various CMOS LSIs operating at cryogenic temperature have been proposed for controlling and reading out qubits. In this paper, I briefly introduce characteristics of transistor and passive devices, such as resistors, capacitors, and inductors, at cryogenic temperature. Then, I review the latest research on cryogenic CMOS circuits for quantum computers.
Superconductor devices are promising for building large-scale quantum computing systems. This article reports the current status and issues of the superconductor classical (digital and mixed-signal) circuit technology for quantum computing applications. The single-flux-quantum-based circuits provide advanced signal processing featuring several gigahertz clock frequencies, high sensitivity, and ultra-low power operation at a millikelvin-level temperature and are helpful for control and readout of quantum bits. The superconductor cryogenic peripheral circuits are expected to be a key to breakthrough in system scalability.
Quantum computer is able to compute some of the hard problems which cannot be solved by conventional ones. Toward practical application, large-scale integration of qubits is necessary. Solid-state devices, such as superconductor and semiconductor qubit devices, are promising candidates to realize the large-scale integration. This paper reviews the current status of research and development of quantum computers based on superconductor and semiconductor devices.
Installing semi-rigid coaxial cables and microwave components in a dilution refrigerator is essential to readout and control superconducting quantum processors. Here we discuss passive and active heat loads generated in the refrigerator and explain techniques to minimize them. Scaling up the size and cooling power of the refrigerator is required in order to operate largely integrated superconducting processors. We also discuss problems impeding the scale up of the refrigerators in Japan and activities in the world.
We are developing a microwave pulse generator, whose pulse width and amplitude can be arbitrarily controlled, to manipulate superconducting quantum computing systems. The proposed microwave pulse generator is made using superconducting circuits. It can be placed at a 4.2 K or lower temperature stages to control a large-scale quantum computing system effectively. One of the key components of the microwave pulse generator is the timing controller, which generates trigger pulses for the microwave switch to start and stop the microwave irradiation. The target frequency of the microwave is 5 GHz, and the timing controller has to generate trigger pulses with a time resolution of several nanoseconds. We designed a 4-bit timing controller using an adiabatic quantum flux parametron (AQFP) circuit, which is extremely energy-efficient superconducting logic. The designed timing controller derives two trigger pulses, start and stop, to the microwave switch at the timing designated by digital data. We implemented the AQFP timing controller using the AIST HSTP process and demonstrated its operation at 1 GHz. Its power dissipation was estimated as about 1.25×10-9 W at 1 GHz.
The application of silicone water repellents to hydrophobic coatings by atmospheric pressure plasma (APP) generated by dielectric barrier discharge (DBD) was investigated. We compared the effects of silicone water repellent on hydrophobic coatings, the input energy density estimated from the voltage-current waveform, and the excitation temperature from the argon line of the measured optical emission spectrum. Hexamethyldisiloxane (HMDSO), KF-96 or KF-99, mixed with argon gas, was supplied as a silicone water repellent to the DBD reactor. The results showed that the irradiated samples became hydrophobic in all cases. Comparing the contact angles of these samples, the contact angle using KF-96 plasma became highly hydrophobic faster than the other conditions. The input power densities to the plasma were about 20 mW/cm2 for KF-96 and KF-99, and 80-110 mW/cm2 for HMDSO. The excitation temperature of argon was 0.9 eV for KF-99, 1 eV for KF-96, and 1.3-2 eV for HMDSO. It reveals that KF-96 is a better silicone water repellent on hydrophobic and input power density than HMDSO.
This paper presents partial discharge characteristics and film thickness wear till dielectric breakdown under bipolar repetitive impulse voltage application to twisted pair enamel wire added with nano-size boehmite to polyimide (PI) resin by comparing with a sample without the addition. The frequency acceleration equivalence of the life time and PD characteristics till breakdown is also examined. As a result, it was found that at frequencies 10 kHz to 30 kHz, a frequency acceleration equivalence held in terms of the total amount of PD charge at an applied voltage Va = 1.5 kV, while it did not at Va = 3.0 kV due to severer heat generated by PD. In addition, it was found that the coating thickness erosion of boehmite PI was less likely to be caused than that of neat PI under the same experimental conditions. Consequently, it is indicated that the total PD charge amount is closely related with the coating erosion speed.
The method to obtain the surface resistivity of insulating materials is standardized by IEC62631-3-2, where four types of line-electrode systems are presented. We have verified the effectiveness of the line-electrode using insulating materials with and without antistatic agent. It is clarified that two types of guard electrodes, edge guard and 2-part back guard, are useful to obtain the resistivity with reliability.
Nb or Ta doped vanadium dioxide (VO2) thin films were grown on r-plane sapphire substrates by a metal-organic decomposition (MOD) method. Their crystallinities of the VO2 thin films were evaluated by XRD, AFM and XPS. It was clarified that polycrystalline fine particles having a moth-eye structure were grown and Nb or Ta ions were gradually replaced by V sites in all the samples. Moreover, it was found that the phase transition temperature measured by a spectrometer indicated 61-39°C for Nb doped samples and 57-47°C for Ta doped samples by doping from 1 to 3 mol%. The change in transmittance before and after the phase transition temperature tended to widen the transition temperature range as the doping concentration increases due to the gradual phase transition change. It was considered that the dopant of Nb or Ta ions added to replace V sites had an effective role on changing the phase transition phenomenon of VO2. Furthermore, FDTD simulation for nanoscale porous moth-eye structure VO2 thin films was carried out to compare with the data measured by a spectrometer, and it was in good agreement.
Since charge injection from metal into dielectric leads to electrical degradation and failure of various electrical and power devices, it is essential to reveal the band alignment of the metal/dielectric interface. However, the band alignment of the metal/dielectric interface remains theoretically unexplored and has not been experimentally obtained. This paper reveals the band alignment at Au/polypropylene (PP) interface by X-ray photoemission spectroscopy (XPS) measurements. The hole injection barrier at the Au/PP interface was measured to be 3.4 eV.