Goro Oohata

Dynamical Fano-Like Interference between Rabi Oscillations and Coherent Phonons in a Semiconductor Microcavity System.

We report on dynamical interference between short-lived Rabi oscillations and long-lived coherent phonons in CuCl semiconductor microcavities resulting from the coupling between the two oscillations. The Fourier-transformed spectra of the time-domain signals obtained from semiconductor microcavities by using a pump-probe technique show that the intensity of the coherent longitudinal optical phonon of CuCl is enhanced by increasing that of the Rabi oscillation, which indicates that the coherent phonon is driven by the Rabi oscillation through the Fröhlich interaction. Moreover, as the Rabi oscillation frequency decreases upon crossing the phonon frequency, the spectral profile of the coherent phonon changes from a peak to a dip with an asymmetric structure. The continuous wavelet transformation reveals that these peak and dip structures originate from constructive and destructive interference between Rabi oscillations and coherent phonons, respectively. We demonstrate that the asymmetric spectral structures in relation to the frequency detuning are well reproduced by using a classical coupled oscillator model on the basis of dynamical Fano-like interference.

Efficient generation of energy-tunable entangled photons in a semiconductor microcavity

A scheme is proposed for the generation of polarization- and frequency-entangled photons in a semiconductor planar microcavity. Photon entanglement can be achieved by converting two lower polariton branches with symmetric in-plane momenta into lower and upper polariton branches with zero in-plane momentum via a biexciton state. The phase-matching condition is satisfied for a microcavity with cavity detuning equal to the biexciton binding energy. The generation efficiency and energy control of the entangled photons are demonstrated for a CuCl microcavity as an example.

Observation of Biexciton-Resonant Hyper-Parametric Scattering in SiO2/CuCl Layered Structures

We have prepared SiO2/CuCl layered structures and investigated the structural and optical properties, focusing on the observation of biexciton-resonant hyper-parametric scattering that is a promising process to generate entangled photons. A crystalline CuCl film, which is the active layer, was grown on an Al2O3 substrate by a vacuum deposition method, and then an amorphous SiO2 film as the passivation layer for hygroscopic CuCl was prepared by an rf-magnetron sputtering method. X-ray diffraction patterns and optical spectra of excitons indicate that the growth of the SiO2-passivation layer does not degrade the crystallinity of the underlying CuCl thin film. It has been demonstrated that the biexciton-resonant hyper-parametric scattering is clearly observable in the SiO2/CuCl layered structure.

Quantitative characterization of highly efficient correlated photon-pair source using biexciton resonance

A high efficiency method for the generation of correlated photon pairs accompanied by reliable means to characterize the efficiency of that process is needed in the study of entangled states, which have important potential applications in quantum information and quantum communication. In this study, we report the first characterization of the efficiency of generation of correlated photon pairs emitted from a CuCl single crystal using the biexciton-resonance hyper-parametric scattering (RHPS) method which is the highly efficient method of generation of correlated photon pairs. In order to characterize the generation efficiency and signal-to-noise ratio of correlated photon pairs using this method, we investigated the pump power dependence on the photon counting rate and coincidence counting rate under resonant excitation. The pump power dependence shows that the power characteristic of the photon counting rates changes from linear to quadratic dependence of the pump power. This behavior represents a superposition of contributions from correlated photon pairs and non-correlated photons. The analysis of the pump power dependence shows that one photon-pair is produced by a pump pulse with 2 x 106 photons. Moreover, the generation efficiency of this method obtained by calculating the number of generated photon pairs per pump power is comparable to that of several methods based on the χ(3) parametric process.

Photon Statistics Analysis of Entangled Photon Pairs via Biexciton Resonant Hyper-Parametric Scattering

We have investigated the quantum statistics of entangled photon pairs generated from biexcitons in CuCl single crystals via resonant hyper-parametric scattering. The generation of multi-photon pairs has been first observed under the high excitation power.

Coherent Control of Terahertz Wave from Coherent Longitudinal Optical Phonon in a GaAs/AlAs Multiple-Quantum-Well Structure

We report on the coherent control of terahertz (THz) waves emitted from coherent longitudinal optical (LO) phonons in a GaAs/AlAs multiple-quantum-well structure at room temperature using two-pulse excitation. When the time difference between the first pump pulse and second weak control pulse is increased, the intensity of THz waves from the coherent phonons is cancelled and enhanced by the control pulse, and the phase of THz waves shows periodic changes accompanied by a phase jump. The time-difference dependences of the intensity and phase of THz waves are explained in terms of the superposition of two coherent oscillations.

Experimental Determination of Excitonic Dispersion Relation from Center-of-Mass Quantization Effect on Excitons in PbI2 Thin Films

We have investigated the center-of-mass quantization effect on excitons in layered-compound PbI 2 ultra-thin films by precisely changing the layer thickness from 7 to 20 monolayers. Crystalline PbI 2 thin films that are fully oriented along the c -axis were prepared by a vacuum deposition method. We confirmed that the surface roughness of the prepared thin films corresponds to one monolayer owing to the van der Waals interaction along the c -axis peculiar to the layered compound, which is advantageous for the realization of the center-of-mass quantization effect. The optical spectra, such as absorption, transmittance, and reflectance clearly exhibit oscillatory structures originating from the quantized excitonic states with a quantum number of up to 15: the quantization energy amounts to ∼130 meV. From the analysis of the systematic results of the center-of-mass quantization, we experimentally determined the excitonic dispersion relation of PbI 2 , which is well explained by a tight-binding exciton model ...