In recent years, there has been increasing interest in quantum computing. In general, the proposed quantum search algorithms such as Grover’s algorithm provide quadratic speedup compared with conventional ones. On the other hand, the quantum walks which can be viewed as the quantum counterparts of the random walks have been received attention as basic models for the quantum computing. In this article, we introduce quantum search method using quantum walks and show its effectiveness.

We review recent developments on quantum chaos and the black hole information problem. Namely, the connection between the Hayden-Preskill thought experiment and out-of-time order correlation functions is discussed.

The kilogram had been the last SI base unit defined by the material artifact. In November 2018, it was adopted to revise the definition by using a defined number of the Planck constant. The new definition came into force on May 20th, 2019, the World Metrology Day. This historical change in the definition of the mass unit was realized by the progress of recent measurement technologies in the Kibble balance and the X-ray crystal density methods. A review is given on these methods, as well as what would be expected by the new definition of the kilogram.

Type II string theory compactified on a torus has the T-duality symmetry. It is a very powerful symmetry but not manifest in the conventional formulation. Double Field Theory (DFT) is a new formulation of supergravity which manifests the T-duality symmetry. In DFT, we introduce an extended space, called the doubled space, and geometry on the doubled space gives a nice description of backgrounds arising in string theory. We explain the geometry of the doubled space and applications of DFT.

Electric-field control of magnetic properties at room temperature has attracted much attention because of its great potential for ultralow-power-consumption electric and spintronic devices. Recently, the electric field effect has been observed not only in semiconductor-based devices but also in metallic ones. In this article, we introduce an electric field effect on interfacial magnetism, specifically, interfacial magnetic anisotropy of ferromagnetic metals. We review experimental studies to reveal the microscopic origin of the electric-field-induced effect using X-ray magnetic circular dichroism spectroscopy.

To implement large-scale quantum computation, the Gottesman-Kitaev-Preskill (GKP) qubit has been recognized as an important technological element. However, it is still challenging to experimentally generate the GKP qubit with the required squeezing level for large-scale quantum computation. To reduce this requirement, we develop a method to prevent the squeezing level from decreasing during the construction of the large-scale cluster. We show that our method with the analog quantum error correction can relax the required squeezing level within the reach of the current experimental technology.

The matter created in non-central heavy-ion collisions should have an initial orbital angular momentum carried by the two colliding nuclei. This angular momentum would be partially transferred to the spin of produced particles due to spin-orbit coupling, leading to the global polarization. The STAR Collaboration observed global polarizations of Λ and Λ(¯) hyperons in Au+Au collisions for collision energies of √S_NN=7.7–200 GeV, indicating the creation of the most vortical fluid ever observed, with vorticity of the order of ω～10²² s^-1. In this article, we review recent results on the polarization measurements and discuss the physics implications.