The fundamental study on tiny mechanical resonators fabricated by state of the art micro and nanofabrication technology is now extensively developed. The advantage to fabricate such small structures is to obtain high frequency resonators. The frequency of mechanical resonance is now over GHz, whose energy quantum corresponds to the thermal energy higher than the base temperature of dilution refrigerator. The tiny mechanical resonators are therefore expected to be experimental testbeds for macroscopic quantum systems. The other important properties are externally controllable nonlinearity. In doubly suspended structures, the internally or externally applied tension can change the resonance frequency and mode function. Beam-splitter-type and parametric amplification interaction can be introduced in the multimode mechanical systems and several demonstration such like coherent control, phonon lasing operation, and 2 mode noise squeezing can be demonstrated. In this article, I review these recent advances reported using the micro and nanomechanical systems.
Nuclear quantum effects of hydrogen nuclei such as zero-point energy and nuclear delocalization significantly influence dynamical and structural properties of condensed hydrogen systems. We report the first computational study on real-time dynamics of hydrogen molecular liquids, solids, and supercooled liquids exhibiting strong nuclear quantum effects which have been hardly accessible by use of previous computational and theoretical methods like density functional theory and semiquantum molecular dynamics simulations with path integrals. All the insights and information we obtained will provide a milestone for identifying and characterizing various unknown hydrogen phases, which will open a new avenue of hydrogen material research.
When a droplet with a higher density falls in a miscible solution with lower density, the droplet deforms and breaks up spontaneously. Instability of a vortex ring, formed by droplet deformation in the falling process, causes the breakup. An origin of the instability, however, is not understood yet. We investigated a relationship between a wavelength of the instability and a thickness of the ring when the instability occurred. The relationship almost agrees with an evaluation of Rayleigh-Taylor (RT) instability. Thus, it is considered that RT instability plays an important role for the instability of the ring. Next, we investigated the number of the breakup. The number depends on a non-dimensional parameter which is a ratio between a driving force by gravity due to a density difference between two solutions and a viscosity dissipation. This means that a balance between the driving force and the viscosity dissipation determines the number.
We review a unique ultrasonic method to detect and image electromagnetic properties of matters. The principle of this method is based on the generation and detection of acoustically stimulated electromagnetic (ASEM) fields originating from electro- or magneto-mechanical coupling. In this paper, we focus on magnetic sensing via ultrasonic excitation. We discuss the mechanism of ASEM response in ferromagnetic materials and demonstrated magnetic imaging and magnetic hysteresis measurements using ultrasonic techniques. This method will be a viable tool not only for nondestructive material inspection but also for fundamental studies of acoustically excited spin dynamics or spin resonance in magnetic thin films and spin devices.