Hiroyuki Katsuki

High Resolution Infrared Absorption Spectra of Methane Molecules Isolated in Solid Parahydrogen Matrices

We present high resolution (∼0.01 cm−1) infrared absorption spectra of the ν4 band of methane doped parahydrogen (CH4/pH2) solids produced by two different techniques: gas condensation in an enclosed cell at T≈8 K, and rapid vapor deposition onto a T≈2 K substrate in vacuum. The spectrum of the rapid vapor deposited solid contains a novel progression of single peaks with ≈5 cm−1 spacing, superimposed over the known spectrum of CH4 molecules trapped in sites of D3h symmetry in hexagonal close-packed (hcp) solid pH2. New theoretical calculations of the rovibrational transitions of a tetrahedral molecule in an external field of Oh symmetry permit the assignment of this new progression to CH4 molecules trapped in crystalline face centered cubic (fcc) regions of the pH2 solid. Annealing of the rapid vapor deposited samples to T≈5 K decreases the intensities of the CH4/pH2(fcc) absorptions, and results in intensity changes for parallel and perpendicularly polarized CH4/pH2(hcp) transitions. We discuss these phe...

Visualizing Picometric Quantum Ripples of Ultrafast Wave-Packet Interference

Interference fringes in vibrating molecules are a signature of quantum mechanics, but are often so short-lived and closely spaced that they elude visualization. We have experimentally visualized dynamical quantum interferences, which appear and disappear in less than 100 femtoseconds in the iodine molecule synchronously with the periodic crossing of two counterpropagating nuclear wave packets. The obtained images have picometer and femtosecond spatiotemporal resolution, representing a detailed picture of the quantum interference.

Tunneling chemical reactions in solid parahydrogen: A case of CD3+H2→CD3H+H at 5 K

Ultraviolet photolysis of CD3I in solid parahydrogen at 5 K gives CD3 radical, which decreases in a single exponential manner with a rate constant of (4.7±0.5)×10−6 s−1. Concomitantly, CD3H is formed, which is accounted for by the quantum tunneling reaction CD3+H2→CD3H+H. Under the same conditions, CH3I yields CH3 radical, but the corresponding reaction between CH3 and H2, expected to give CH4+H, does not proceed measurably at 5 K. The difference between the two systems is attributed to the difference in the zero point energy change.

High-resolution laser spectroscopy of methane clusters trapped in solid parahydrogen

Clusters of methane are isolated in solid parahydrogen. The vibrational spectral region of the ν4 fundamental of methane molecule is surveyed with a Fourier transform infrared spectrometer and a high-resolution difference-frequency infrared laser system. More than 200 sharp absorption lines are discovered whose linewidth is as narrow as 0.007 cm−1 (200 MHz). The spectrum indicates that the rovibrational levels of the clusters of small sizes are well quantized in solid parahydrogen.

All-optical control and visualization of ultrafast two-dimensional atomic motions in a single crystal of bismuth

In a bulk solid, optical control of atomic motion provides a better understanding of its physical properties and functionalities. Such studies would benefit from active control and visualization of atomic motions in arbitrary directions, yet, so far, mostly only one-dimensional control has been shown. Here we demonstrate a novel method to optically control and visualize two-dimensional atomic motions in a bulk solid. We use a femtosecond laser pulse to coherently superpose two orthogonal atomic motions in crystalline bismuth. The relative amplitudes of those two motions are manipulated by modulating the intensity profile of the laser pulse, and these controlled motions are quantitatively visualized by density functional theory calculations. Our control-visualization scheme is based on the simple, robust and universal concept that in any physical system, two-dimensional particle motion is decomposed into two orthogonal one-dimensional motions, and thus it is applicable to a variety of condensed matter systems.

SF6 and its clusters in solid parahydrogen studied by infrared spectroscopy

The triply degenerate stretching vibration of sulfur hexafluoride and its clusters in solid parahydrogen at cryogenic temperatures is studied using Fourier transform infrared spectroscopy. The observed spectra are compared with theoretical spectra constructed on the basis of the intermolecular resonant dipole–dipole and the dipole–induced-dipole interactions. The absorptions due to monomer, dimer, trimer, and tetramer are discussed individually.

Implementation of quantum gate operations in molecules with weak laser fields.

We numerically propose a way to perform quantum computations by combining an ensemble of molecular states and weak laser pulses. A logical input state is expressed as a superposition state (a wave packet) of molecular states, which is initially prepared by a designed femtosecond laser pulse. The free propagation of the wave packet for a specified time interval leads to the specified change in the relative phases among the molecular basis states, which corresponds to a computational result. The computational results are retrieved by means of quantum interferometry. Numerical tests are implemented in the vibrational states of the B state of I2 employing controlled-NOT gate, and 2 and 3 qubits Fourier transforms. All the steps involved in the computational scheme, i.e., the initial preparation, gate operation, and detection steps, are achieved with extremely high precision.

Observation of discrete energy states of weakly confined vibron in solid parahydrogen

The first overtone pure vibrational Q2(0) [v=2←0, J=0←0] transition of solid parahydrogen was studied using high-resolution laser spectroscopy. The absorption spectrum exhibits extremely narrow linewidths (20 MHz full-width-at-half-maximum), which allowed us to observe rich spectral structure in the transition. Part of the structure is attributed to the M sublevel splitting of orthohydrogen that induces dipole moments on surrounding parahydrogen molecules, but the finer spectral structure is due to vibron hopping of the v=2 excited state of parahydrogen molecules. The Stark field of the orthohydrogen localizes the vibron on a finite number of parahydrogen molecules, which results in the discrete vibron states. From the analysis of the spectral structure, the vibron hopping frequency of the v=2 state is determined to be −114 MHz. It is also found that the spectral structure cannot be explained completely unless the quantum nature of solid hydrogen is taken into account for the analysis.

Optically pumped lasing in single crystals of organometal halide perovskites prepared by cast-capping method

A simple “cast-capping” method is adopted to prepare single-crystal perovskites of methyl ammonium lead bromide (CH3NH3PbBr3). By capping a CH3NH3PbBr3 solution casted on one substrate with another substrate such as glass, mica, and distributed Bragg reflector (DBR), the slow evaporation of solvent enables large-size cubic crystals to grow between the two substrates. Under optical pumping, edge-emitting lasing is observed based on Fabry–Perot resonation between parallel side facets of a strip-shaped crystal typically with a lateral cavity length of a few tens of μm. On the other hand, vertical-cavity surface-emitting lasing (VCSEL) is obtained from a planar crystal grown between two DBRs with a cavity thickness of a few μm. Simultaneous detection of those edge- and surface-emissions reveals that the threshold excitation fluence of VCSEL is higher than that of the edge-emitting lasing due to thickness gradient in the planar crystal.

Quantum property of solid hydrogen as revealed by high-resolution laser spectroscopy

Pure vibrational overtone transitions of solid parahydrogen are studied using high-resolution laser spectroscopy. Extremely narrow spectral linewidth (∼20 MHz) allows us to observe rich spectral structure that originates in subtle intermolecular interactions in the crystal. It is found that anisotropy of the distribution of zero-point lattice vibration of hydrogen molecules perturbs the energy levels of the vibrationally excited states significantly. A large amplitude of zero-point lattice vibration, an intrinsic propoerty of quantum solids, is directly observed from the present high-resolution spectroscopy. The first observation of a pure vibrational overtone transition of solid orthodeuterium is also discussed.