Reservoir computing is a framework for computation such that:(1) an input signal is given to a dynamical system (reservoir); (2) the input sequence is encoded by the high-dimensional dynamics of the reservoir; and (3) the desired output is formed by a simple readout mechanism of the reservoir. Recently, physical reservoir computing, which utilizes real physical systems as the reservoir, has attracted attention in the fields of nonlinear physics and machine learning. As an application of reservoir computing, we report the characteristics of the reservoir composed of neural networks which are optimized by recurrent informax principle.

Terahertz radiation from a solid with no inversion symmetry irradiated with a femtosecond laser pulse is widely used as a light source in spectroscopy in the terahertz region. In this paper, we report that such a terahertz-radiation process itself can be used to study physical properties of solids associated with ferroelectric polarization and ferromagnetic magnetization, and their sub-picosecond dynamics. We show that a terahertz wave is emitted via the electric-dipole radiation mechanism from organic ferroelectrics and can be utilized to map out ferroelectric domain structures. We also demonstrate that the magnetic domain imaging in ferro (ferri)-magnets is possible by detecting a terahertz radiation induced via the magnetic-dipole radiation. In addition, we report new kinds of terahertz-radiation phenomena; a terahertz radiation with high efficiency in a photoinduced ferroelectric to paraelectric transition, a narrow-band terahertz radiation by an impulsive stimulated Raman process, and a terahertz radiation by a spin-polarized current.

The scissors mode is a collective, orbital M1 excitation found in deformed atomic nuclei, and is considered an oscillation of the protons against the neutrons in a scissors like fashion. In recent measurements of the scissors mode in radiative decay experiments, transition strengths were observed that were double that expected from systematics established from measurements using nuclear resonance fluorescence (NRF). Additional strength in NRF measurements can only be present as heretofore unobserved branching or fragmentation of the scissors mode. Such possibilities were investigated in a transmission NRF measurement on the deformed ¹⁸¹Ta using a quasi-monoenergetic γ-ray beam generated by laser Compton scattering at High Intensity γ-ray Source (HIγS) facility, Duke University. A large branching of fragmented small resonances to excited states was discovered. The results could reconcile the scissors mode strength observed in NRF measurements with the expectations for enhanced scissors mode strength from radiative decay experiment.