Since the first indication in 1930s, the dark matter in the universe has been studied in many ways. Astronomical observations pinned down the total amount of the dark matter in the universe and its existence is widely accepted. In spite of intensive studies of the dark matter in the theoretical and experimental ways, its nature is still unknown. Among many candidates of the dark matter, Weakly Interacting Massive Particle (WIMP) is said to be the leading candidate of the dark matter. This is because that WIMPs can not only solve the dark matter problem, but the abundance of the dark matter today can naturally be explained by so-called thermal relic scenario. In the thermal-relic scenario, the dark matter was created in the early universe and annihilated during the evolution of the universe until it is freeze-out by the expansion of the universe. WIMPs can be detected through the interaction with ordinary matters as the nuclear recoil signals in particle detectors. The dark matter search using this recoil interactions is referred to as the direct detection and many experimental efforts have been made so far. Two-phase, liquid and gas, Xenon detectors are leading the direct searches. Several-tons of these detectors are being build and first discovery of the dark matter would happen any time in a few years.
Optical manipulation of magnetic order is one of the attracting themes in condensed matter physics not only for its fundamental importance but also for the potential technological application. It is known that a promising strategy is to control the exchange interaction by light irradiation. In this research, we examine the double-exchange interaction, which has been recognized as a typical ferromagnetic interaction in metallic compounds. We discover that the double exchange interaction is an “antiferromagnetic interaction” in photoinduced nonequilibrium states. It is also found that, in a transient time domain between the ferromagnetic metal and the photoinduced antiferromagnetic state, the topological spin structure appears. The microscopic mechanism and experimental inspection methods are also introduced.
Inspired by bifurcation-based adiabatic quantum computation and its classical counterpart, we propose a new heuristic algorithm for combinatorial optimization: simulated bifurcation (SB), which is based on classical adiabatic and ergodic evolutions. The SB enables ultrafast and large-scale combinatorial optimization using conventional digital computers.
Molecular kinetics in condensed phase systems varies from species to species: some show rapid change, but others are slower. However, while the nature of this process is vital for understanding various molecular phenomena, the underlying mechanism remains unclear. Our recent study where molecular dynamics simulations were conducted for LiCl, NaCl, KCl, and CsCl in water revealed the origin of different rate constants for the ion-pair dissociation process. Analysis of the free-energy landscape with a solvent reaction coordinate showed that the differences in the ion-pair dissociation rates arose predominantly from the variation in solvent-state distribution between the ion pairs. The formation of a water-bridging configuration was identified as a key step in this process. This understanding will contribute to future explorations of many other molecular events such as surface water exchange and protein–ligand dissociation.