Fiber-cavity ring-down temperature sensor using a transmissive configuration combined with the heterodyne detection technique.

A fiber Bragg grating temperature sensor based on the cavity ring-down technique is reported. A quasi-linear fiber cavity is proposed to reduce optical loss in the cavity instead of a conventional fiber-loop configuration. The heterodyne detection technique is applied to sensitively detect weak pulses from the cavity.

Optical Imaging of a Single Molecule with Subnanometer Resolution by Photoinduced Force Microscopy.

Visualizing the optical response of individual molecules is a long-standing goal in catalysis, molecular nanotechnology, and biotechnology. The molecular response is dominated not only by the electronic states in their isolated environment but also by neighboring molecules and the substrate. Information about the transfer of energy and charge in real environments is essential for the design of the desired molecular functions.

Enantioselective optical trapping of single chiral molecules in the superchiral field vicinity of metal nanostructures.

In this study, we theoretically analyzed the optical force acting on single chiral molecules in the plasmon field induced by metallic nanostructures. Using the extended discrete dipole approximation, we quantitatively examined the optical response of single chiral molecules in the localized plasmon by numerically analyzing the internal polarization structure of the molecules obtained from quantum chemical calculations, without phenomenological treatment. We evaluated the chiral gradient force due to the optical chirality gradient of the superchiral field near the metallic nanostructures for chiral molecules.

Near-field circular dichroism of single molecules.

Near-field images of molecules provide information about their excited orbitals, giving rise to photonic and chemical functions. Such information is crucial to the elucidation of the full potential of molecules as components in functional materials and devices at the nanoscale. However, direct imaging inside single molecules with a complex structure in the near-field is still challenging because it requires in situ observation at a higher resolution than the molecular scale.

Entangled two-photon absorption spectroscopy for optically forbidden transition detection.

We theoretically propose a spectroscopic method for measuring optically forbidden states using entangled two-photon absorption (TPA). As a model system, we consider a diatomic molecular system consisting of three adiabatic potentials, namely, ground, intermediate, and excited states, where the intermediate state cannot be directly excited from the ground state. In our method, we pump the excited state using entangled TPA and indirectly measure the optically forbidden intermediate state through the photon emission from the excited state to the intermediate state.

Simple model of saturable localised surface plasmon.

Localised surface plasmons (LSPs) are now applied to various fields, such as bio-sensing, solar cell, molecular fluorescence enhancement and quantum-controlled devices at nanometre scale. Recent experiments show that LSPs are optically saturated by high-intensity light. Absorption saturation arises as a result of strong optical nonlinearity and cannot be explained by the conventional boson model of LSPs.

Generation of broadband ultraviolet frequency-entangled photons using cavity quantum plasmonics.

Application of quantum entangled photons is now extending to various fields in physics, chemistry and biology. In particular, in terms of application to molecular science, broadband ultraviolet frequency-entangled photons are desired because molecules inducing photochemical reactions of interest often have electronic transition energies in the ultraviolet region. Recent standard method for generating such entangled photons is a chirped quasi-phase-matching method, however this method is not suitable for the generation of ultraviolet frequency-entangled photons because it requires down-conversion of a photon with a wavelength shorter than ultraviolet into an entangled photon pair.

Role of an elliptical structure in photosynthetic energy transfer: Collaboration between quantum entanglement and thermal fluctuation.

Recent experiments have revealed that the light-harvesting complex 1 (LH1) in purple photosynthetic bacteria has an elliptical structure. Generally, symmetry lowering in a structure leads to a decrease in quantum effects (quantum coherence and entanglement), which have recently been considered to play a role in photosynthetic energy transfer, and hence, elliptical structure seems to work against efficient photosynthetic energy transfer. Here we analyse the effect of an elliptical structure on energy transfer in a purple photosynthetic bacterium and reveal that the elliptical distortion rather enhances energy transfer from peripheral LH2 to LH1 at room temperature.

Control of vibronic excitation using quantum-correlated photons.

We theoretically investigate the two-step excitation of a molecular vibronic state using quantum-correlated photons with time delay in order to control the population of the vibronic excited state. A Morse oscillator having three sets of vibronic states, namely, the ground state, intermediate states, and excited states, is used to evaluate the efficiency of the two-step excitation process. We show that we can efficiently and selectively excite only a target state by using correlated photons and can control the excitation population of the target state by adjusting the delay time of the correlated photons.

Selective two-photon excitation of a vibronic state by correlated photons.

We theoretically investigate the two-photon excitation of a molecular vibronic state by correlated photons with energy anticorrelation. A Morse oscillator having three sets of vibronic states is used, as an example, to evaluate the selectivity and efficiency of two-photon excitation. We show that a vibrational mode can be selectively excited with high efficiency by the correlated photons, without phase manipulation or pulse-shaping techniques.

Efficient two-step up-conversion by quantum-correlated photon pairs.

We theoretically investigate the sequential two-step upconversion of correlated photon pairs with positive and negative energy correlations, in terms of how the up-conversion efficiency depends on the incident pulse delay. A three-level atomic system having a metastable state is used to evaluate the up-conversion efficiency. It is shown that a photon pair with a positive energy correlation can drastically enhance the up-conversion efficiency compared with uncorrelated photons and correlated photons with a negative energy correlation.

Highly efficient generation of entangled photons by controlling cavity bipolariton states.

We theoretically investigate entangled-photon generation via a biexciton in a planar microcavity. Owing to strong exciton-photon coupling, the biexciton in the cavity produces a bound two-cavity-polariton state (cavity bipolariton). Entangled photons are generated by the cascade decay of the cavity bipolariton.