Atsushi Yabushita

Primary Conformation Change in Bacteriorhodopsin on Photoexcitation

Ultrafast dynamics of bacteriorhodopsin (bR) has been extensively studied experimentally and theoretically. However, there are several contradictory results reported, indicating that its detailed dynamics and initial process have not yet been fully clarified. In this work, changes in the amplitude and phase of molecular vibration in the isomerization process of bR were real-time probed simultaneously at 128 different wavelengths through intensity modulation of the electronic transition. Systematic information on the transient change in continuous spectrum extending from 505 nm (2.45 eV) to 675 nm (1.84 eV) showed different dynamics in each spectral region reflecting the difference in the excited states and intermediates dominating the dynamics during the photoisomerization. Careful analysis of the transient spectral changes and spectrograms calculated from the vibrational real-time traces elucidated that the primary event just after photoexcitation is the deformation of the retinal configuration, which decays within 30 fs near the C=N bond in the protonated Schiff base. The intensity of C=N stretching mode starts to decrease before the initiation of the frequency modulation of the C=C stretching mode. The C=C stretching mode frequency was modulated by a coupled torsion around the C13=C14 bond, leading to the photoisomerization around the bond. This study clarified the dynamics of the C=N and C=C stretching modes working as key vibration modes in the photoisomerization of bR. Furthermore, we have elucidated the modulation and decay dynamics of the C=C stretching mode in the photoreaction starting from H (Franck-Condon excited state) followed by I (twisted excited), and J (first intermediate) states.

SHG FROG and XFROG methods for phase/intensity characterization of pulses propagated through an absorptive optical medium

Abstract Second-harmonic generation frequency-resolved optical gating and cross-correlation frequency-resolved optical gating were used as a characterization method of the phase and amplitude of pulses propagated through a 0.5-mm-thick plate of Nd 3+ -doped glass. Both experimental results of field intensity and phase were in fair agreement with the calculated result.

Sub‐5‐fs Real‐time Spectroscopy of Transition States in Bacteriorhodopsin During Retinal Isomerization†

The C=C stretching mode of bacteriorhodopsin was modulated by torsion of the C13=C14 double bond with a period of 200 fs. The real-time data elucidates the relations among the real-time torsion angle, bond order.

Generation of frequency tunable polarization entangled photon pairs

Photon pairs with correlated frequencies from an optical parametric system were generated by a continuous wave pump focused on a type-II nonlinear crystal with polarization entanglement. The polarization entanglement of the frequency resolved photons was measured under several typical configurations. By optimizing a condition, the degree of polarization entanglement was improved substantially. We proposed the application of the system, which can be used as a light source of wavelength division multiplexing quantum key distribution, optimizing the configuration of the photon-pair generation.

Quantum key distribution with a heralded single photon source and a photon number resolving detector

We have experimentally demonstrated quantum key distribution with a heralded single photon source and a photon number resolving detector. Numerical calculations have shown the expansion of the distance.

Chirped Molecular Vibration During Photo-Isomerization in Stilbene Derivative in Solution

The photoisomerisation reaction of 4-methoxy-4-nitrostilbene in condensed phase was studied by femtosecond pump probe spectroscopy. Transient changes in absorption intensity exhibit oscillations which reflect chirped vibrational motions on the potential surface.The photoisomerisation reaction of 4-methoxy-4-nitrostilbene in condensed phase was studied by femtosecond pump probe spectroscopy. Transient changes in absorption intensity exhibit oscillations which reflect chirped vibrational motions on the potential surface.