Diamond is an ultrawide band gap semiconductor exhibiting exceptionally high breakdown voltage, radiation tolerance, and thermal conductivity. Owing to the high exciton binding energy originating from the wide bandgap, diamond provides an attractive arena to explore quantum many-body physics on coexistent states of charge carriers, excitons, and their complexes. The recent progress in the experimental approach to the optical properties of photoexcited diamond is introduced along with the prospects of the research.

Dirac semimetals have so-called Dirac cone in three-dimensional bulk electronic structures. They also have a unique bulk-surface coupled electronic state, and so they have attracted growing attention as a material system for next generation electronics. In this review, we will explain fundamental features of Cd₃As₂, a typical Dirac semimetal, and introduce a series of our results ranging from fabrication of high-quality thin films to finding of a unique quantum Hall state. We will also summarize future prospects for possible applications.

The superconducting diode effect is a phenomenon that results in a superconducting state with zero electrical resistance in the forward direction, but a normal conducting state with finite resistance in the reverse direction. The similarity of this effect to the semiconductor diode, one of the building blocks of current electronic devices, can lead to its application in diodes and rectifiers, which can be used with ultra-low power consumption. Recently, the zero-field superconducting diode effect controlled by magnetization has been demonstrated. This opens up new possibilities for using magnetization to control superconductivity. Here, we give an overview of the superconducting diode effect and discuss future prospects.

We have recently introduced a new quantum control approach by combining an ultracold Rydberg atom array with ultrafast lasers. In this paper, we describe the two fundamental technologies behind this new system: optical tweezers to capture individual single atoms that make up the atomic array, and pulse-laser technology to control the quantum states of those single atoms in the picosecond timescale. In addition, we present an ultrafast two-qubit gate that operates at the quantum speed limit, in a few nanosecond, achieved thanks to these novel concepts. This gate is an innovation that accelerates the conventional two-qubit gate for cold-atom quantum computer by two orders of agnitude.

We present the effects of size characterized by the disorder parameter on electrical and optical properties in high Hall mobility transparent conductive oxide (TCO) films. We deposited amorphous W-doped In₂O₃ (IWO) films with thicknesses ranging from 5 to 10 nm on glass substrates by reactive plasma deposition with dc-arc discharge. For polycrystalline IWO films with solid-phase crystallization, we have elucidated the dominant factors determining the states of carrier electrons and the carrier transport. A decrease in the thicknesses from 10 to 5 nm with retaining carrier concentration, leading to 2D-like films materials, induced the disorder, resulting in a deterioration in Hall mobility. Theoretically obtained electron-phonon coupling factor governed by Debye temperature, carrier concentration and the disorder provides the cause of the above carrier transport, together with the issue to achieve high carrier transport ultra-thin TCO films.

In recent years, various 3D printing technologies have been developed, enabling the fabrication of 3D structures of ceramics and glass, in addition to resin and metal. However, several issues remain, such as expanding the printable size, improving processing accuracy, and shortening manufacturing time. To address these challenges, we have developed both stereolithography methods and photocurable materials that can fabricate glass and ceramic parts in several hours of sintering. We have also developed multi-material stereolithography techniques to produce functional 3D-printed parts. In this paper, we introduce examples of various ceramic parts fabricated by our methods. Photocurable materials that enable high-speed sintering will be discussed, and examples of 3D-printed glass structures will be presented.

Consecutive multiple shots of femtosecond laser pulses can directly form periodic nanostructures on solid surfaces through ablation. Because the period is much smaller than the diffraction limit of light, this phenomenon is expected to be applied to nanofabrication technology. In this paper, we introduce the formation mechanism of the nanostructure and its applications.

Electron-spin-resonance (ESR) spectroscopy is a powerful tool for studying point defects in semiconductor crystals. EDMR (electrically detected magnetic resonance) enables us to detect ESR signals in miniaturized semiconductor devices. Using EDMR, the authors have identified various interface defects at 4H-SiC/SiO₂ interfaces. This paper presents the details of our EDMR instrument and our EDMR experiments on 4H-SiC MOSFETs (metal-oxide-semiconductor field-effect transistors) using the two typical examples: EDMR detections of a typical MOS interface defect (the P_bC center = interfacial carbon dangling-bond defect) and a typical spin defect (the T_V2a center = silicon vacancy) in 4H-SiC MOSFETs.