A quantum convolutional neural network on NISQ devices

Quantum machine learning is one of the most promising applications of quantum computing in the noisy intermediate-scale quantum (NISQ) era. We propose a quantum convolutional neural network(QCNN) inspired by convolutional neural networks (CNN), which greatly reduces the computing complexity compared with its classical counterparts, with O((log2M)6) basic gates and O(m2+e) variational parameters, where M is the input data size, m is the filter mask size, and e is the number of parameters in a Hamiltonian. Our model is robust to certain noise for image recognition tasks and the parameters are independent on the input sizes, making it friendly to near-term quantum devices. We demonstrate QCNN with two explicit examples. First, QCNN is applied to image processing, and numerical simulation of three types of spatial filtering, image smoothing, sharpening, and edge detection is performed. Secondly, we demonstrate QCNN in recognizing image, namely, the recognition of handwritten numbers. Compared with previous work, this machine learning model can provide implementable quantum circuits that accurately corresponds to a specific classical convolutional kernel. It provides an efficient avenue to transform CNN to QCNN directly and opens up the prospect of exploiting quantum power to process information in the era of big data.

Tuning the electronic states and superconductivity in alkali fulleride films

The successful preparation of superconducting alkali fulleride (AxC60, A = K, Rb, Cs) films using state-of-the-art molecular beam epitaxy overcomes the disadvantages of the air-sensitivity and phase separation in bulk AxC60, enabling for the first time a direct investigation of the superconductivity in alkali fullerides on the molecular scale. In this paper, we briefly review recent cryogenic scanning tunneling microscopy results of the structural, electronic, and superconducting properties of the fcc AxC60 films grown on graphitized SiC substrates. Robust s-wave superconductivity is revealed against the pseudogap, electronic correlation, non-magnetic impurities, and merohedral disorder. By controlling the alkali-metal species, film thickness, and electron doping, we systematically tune the C60x− orientational orderings and superconductivity in AxC60 films and then complete a unified phase diagram of superconducting gap size vs electronic correlation and doping. These investigations are conclusive and elucidated that the s-wave superconductivity retains in alkali fullerides despite of the electronic correlation and presence of pseudogap.

β-Ga2O3 material properties, growth technologies, and devices: a review

Rapid progress in β-gallium oxide (β-Ga2O3) material and device technologies has been made in this decade, and its superior material properties based on the very large bandgap of over 4.5 eV have been attracting much attention. β-Ga2O3 appears particularly promising for power switching device applications because of its extremely large breakdown electric field and availability of large-diameter, high-quality wafers manufactured from melt-grown bulk single crystals. In this review, after introducing material properties of β-Ga2O3 that are important for electronic devices, current status of bulk melt growth, epitaxial thin-film growth, and device processing technologies are introduced. Then, state-of-the-art β-Ga2O3 Schottky barrier diodes and field-effect transistors are discussed, mainly focusing on development results of the author’s group.

On the renormalization of entanglement entropy

The renormalization of entanglement entropy of quantum field theories is investigated in the simplest setting with a λϕ4 scalar field theory. The 3+1 dimensional spacetime is separated into two regions by an infinitely flat 2-dimensional interface. The entanglement entropy of the system across the interface has an elegant geometrical interpretation using the replica trick, which requires putting the field theory on a curved spacetime background. We demonstrate that the theory, and hence the entanglement entropy, is renormalizable at order λ once all the relevant operators up to dimension 4 are included in the action. This exercise has a one-to-one correspondence to entanglement entropy interpretation of the black hole entropy which suggests that our treatment is sensible. Our study suggests that entanglement entropy is renormalizable and is a physical quantity.

Surface atomic-layer superconductors with Rashba/Zeeman-type spin-orbit coupling

In this article, we review the recent progress in surface atomic-layer superconductors on semiconductor substrates with Rashba/Zeeman-type spin-orbit coupling (SOC). After introduction of some of the basics of Rashba/Zeeman-type SOC and its effects on superconductivity, representative surface structures with relevant features are described in terms of their crystalline and electronic properties. This is followed by recent experimental studies that have revealed anomalous superconducting phenomena, which can be attributed to the effects of Rashba/Zeeman-type SOC. Future prospects, likely to be driven by instrumentational developments, are given as a concluding remark.

Fast and versatile polarization control of X-ray by segmented cross undulator at SPring-8

An X-ray is the well-known probe to examine structure of materials, including our own bodies. The X-ray beam, especially at the wavelength of nanometers, has also become significant to directly investigate electronic states of a sample. Such an X-ray is called a soft X-ray and polarization dependence of the light-matter interaction further unveils the microscopic properties, such as orbitals or spins of electrons. Generation of high brilliant beams of the polarized X-ray has linked to development of our experimental science, and it has been made by radiation from relativistic electrons at the synchrotron radiation facilities over the world. Recently, we constructed a new polarization-controlled X-ray source, the segmented cross undulator, at SPring-8, the largest synchrotron radiation facility in the world. The operation is based on interference of X-ray beams, which is sharply contrast to the conventional method of regulating electron trajectory by the mechanical control of magnets. The paradigm shift opened the measurement innovations and allowed us to design new experimental approaches to capture signals that have been hidden in materials. The present review describes the novel X-ray source with the principle of operation and the technical details of optimization. Examples of the frontier spectroscopies that use unique optical properties of the source are introduced, followed by the future prospects for next generation synchrotron radiation facilities.

Plasma bubbles: a route to sustainable chemistry

Atmospheric plasma discharges are finding increased applications in addressing environmental challenges including water purification, chemical synthesis and biotechnology. An effective means of interfacing the reactivity of plasma gas discharges with liquids is needed to enhance liquid phase chemical reactions. Plasma discharges in bubbles has been considered as an innovative solution for achieving this goal potentially offering electrically driven, sustainable chemistry with low energy consumption and the unique benefit of maintaining a large volume discharge under the liquid surface. Here we provide a concise review on the state-of-art for research on plasma-bubble interactions and a perspective for future research.

High-power proton accelerators for pulsed spallation neutron sources

With the spread of accelerator-driven pulsed spallation neutron sources and increasing need for higher neutron fluxes, the high-power performance of proton accelerators has greatly advanced from a few kilowatts to more than 1 MW in the last four decades. The most important concerns to realize such a high-power beam operation are controlling and minimizing beam loss, which are essential for sustainable beam operation that allows hands-on maintenance. This paper reviews key devices and beam handling techniques for beam loss control employed in the high-power proton accelerators that are currently in operation for pulsed spallation neutron sources, including their operational status and future upgrade plan.

Neutron applications developing at compact accelerator-driven neutron sources

Neutrons have been used in a wide field of applications by using various neutron sources. Material science is one of the widest research fields. The activity is supported by nuclear research reactors and high-intensity spallation neutron sources based on a high-intensity proton accelerator. However, it is desired to perform a measurement when researchers want to do and to perform adventuresome experiments that have not yet confirmed its importance. Furthermore, trial and error measurements are necessary to improve a measurement method. Compact accelerator-driven neutron sources are suitable for such usage and in some cases can complement the measurement at a large facility. The use of the compact neutron source has sometimes led to new methods. Other than material science, a new application of soft error acceleration test has been performed at the compact accelerator-driven neutron sources. Another neutron application is radiation therapy called as boron neutron capture therapy. In this field, nuclear reactor neutron sources have been used but many of them shut down. It was desired to construct the BNCT facility near a hospital. Therefore, BNCT facilities based on the compact accelerator have been constructed in the world. Here, the neutron sources and new methods and applications developing at compact accelerator-driven neutron sources are introduced.