Munehiro Nishida

Development of a mass-producible on-chip plasmonic nanohole array biosensor

We have developed a polymer film based plasmonic device whose optical properties are tuned for measuring biological samples. The device has a circular nanohole array structure fabricated with a nanoimprint technique using a UV curable polymer, and then gold thin film is deposited by electron beam deposition. Therefore, the device is mass-producible, which is also very important for bioaffinity sensors. First the gold film thickness and hole depth were optimized to obtain the maximum dip shift for the reflection spectra. The dip shift is equivalent to the sensitivity to refractive index changes at the plasmonic device surface. We also calculated the variation in reflection spectra by changing the above conditions using the finite-difference time domain method, and we obtained agreement between the theoretical and experimental curves. The nanohole periodicity was adjusted from 400 to 900 nm to make it possible to perform measurements in the visible wavelength region to measure the aqueous samples with less optical absorption. The tuned bottom filled gold nanohole array was incorporated in a microfluidic device covered with a PDMS based microchannel that was 2 mm wide and 20 μm deep. As a proof of concept, the device was used to detect TNF-α by employing a direct immunochemical reaction on the plasmonic array, and a detection limit of 21 ng mL(-1) was obtained by amplification with colloidal gold labeling instead of enzymatic amplification.

Multipole surface plasmons in metallic nanohole arrays

The quasi-bound electromagnetic modes for the arrays of nanoholes perforated in thin gold film are analyzed both numerically by the rigorous coupled wave analysis (RCWA) method and semi-analytically by the coupled mode method. It is shown that when the size of the nanohole occupies large portion of the unit cell, the surface plasmon polaritons (SPPs) at both sides of the film are combined by the higher order waveguide modes of the holes to produce multipole surface plasmons: coupled surface plasmon modes with multipole texture on the electric field distributions. Further, it is revealed that the multipole texture either enhances or suppresses the couplings between SPPs depending on their diffraction orders and also causes band inversion and reconstruction in the coupled SPP band structure. Due to the multipole nature of the quasi-bound modes, multiple dark modes coexist to produce variety of Fano resonance structures on the transmission and reflection spectra.

Time Dilation of a Bound Half-Fluxon Pair in a Long Josephson Junction with a Ferromagnetic Insulator

The fluxon dynamics in a long Josephson junction with a ferromagnetic insulating layer is investigated. It is found that the Josephson phase obeys a double sine-Gordon equation involving a bound pi fluxon solution, and the internal oscillations of the bound pair acting as a clock exhibit Lorentz reductions in their frequencies regarded as a relativistic effect in the time domain, i.e., time dilation. This is the complement to the Lorentz contraction of fluxons with no clock. A possible observation scheme is also discussed.

Superconducting and density-wave correlation functions in carbon nanotubes

Abstract We discuss the phase diagrams obtained by calculating temperature dependences of superconducting and density-wave correlation functions for a single (5,0) carbon nanotube (CN). We use one-loop renormalization group method within logarithmic accuracy. In this system, we must specify scattering channels in terms of momentum along the circumferential direction as well as the axis direction, because (5,0) CN has two degenerate bands crossing the Fermi energy with circumferential momenta. We find that the most divergent order is singlet superconducting or charge-density wave with 0 or 10 π ℏ/2 πR circumferential momentum, where R is the tube radius.

Detection of Antigen-Antibody Reaction Using Si Ring Optical Resonators Functionalized with an Immobilized Antibody-Binding Protein

We propose the integrated biosensor chip using Si ring resonators, where different receptor is immobilized on each sensor. Signal detection is carried out by the matrix of light-input and detection waveguides, which are respectively connected to laser diodes and photodetectors. The Si rings are arranged at the cross points. The unique point of our work is to use the silicon-binding protein (designated Si-tag), which binds to SiO2 surface, as an anchoring molecule to immobilize bioreceptor on the Si rings in an oriented manner. In the integrated biosensor chip, many kinds of Si-tag-receptor fusions are required for high-throughput detection of analyte. In this paper, the Si ring biosensors were functionalized with various antibodies using the Si-tagged protein A as an intermediate binder, and the label-free detection of antigen have been achieved. We have developed the rapid functionalization method of Si-ring resonators with antibodies using Si-tagged protein A. Since various kinds of antibody can be used as receptors for biosensing, this method promises to realize the integrated biosensors for high-throughput analyte detection. # 2011 The Japan Society of Applied Physics

Mobile fluxon qubits in a long superconductor-ferromagnet-superconductor Josephson junction

We propose a new type of mobile qubit that utilizes a bound pair of half fluxons in a long superconductor-ferromagnet-superconductor (SFS) Josephson junction. The qubit states are composed of the lowest two levels of the quantized nonlinear internal oscillation of the bound pair. The energy levels are estimated by the numerical quantization based on a collective coordinate method. The qubit operation scheme is discussed, showing an estimate of the interaction strength between a bound pair and a microcircuit.

The effect of dissipation on quantum transmission resonance

Quantum transmissions of a free particle passing through a rectangular potential barrier with dissipation are studied using a path decomposition technique. Dissipative processes strongly suppress the transmission probability at resonance just above the barrier resulting in an unexpected reduction of the mean traversal time through the potential barrier.

Flying Superconducting Qubits

A flying qubit is proposed that uses an elementary excitation in superconducting nanocircuits including Josephson transmission lines. Our proposed qubit can resolve an existing qubit-manipulation problem that is unavoidable in solid-state based quantum computers, and has the potential for integrating computation and communication using its flying nature. A concrete example is provided of quantum logic gates using our proposed qubit.

Theory of Photocurrent in BCS Excitons

We derive a photocurrent formula for a hybrid semiconductor junction with an excitonic Bardeen‐Cooper‐Schrieffer (BCS) state. The formula provides a new approach to confirm the excitonic BCS state as well as its potential for applications like solar cells.

Dual Aharonov–Casher effect in singlet-exciton systems

Abstract Dual Aharonov–Casher (DAC) phase (or He–McKellar–Wilkens phase), which is defined as a quantum topological phase acquired by a neutral particle only with an electric dipole moment μE being taken on a closed path around a magnetic monopole wire, is theoretically investigated in singlet-exciton systems. In the Sangsters interference scheme, a moving 2s exciton in magnetic fields feels an effective electric field in co-moving frame, which causes a superposition of opposite parity states, i.e., |2s〉 and |2p〉, due to the motional Stark effect. The superposition gives rise to a nonvanishing electric dipole moment required for the DAC effect to the exciton. The accumulated phase is determined by detecting photon emissions from 2p states as a function of applied magnetic fields.