International Journal of Modern Physics B

A number of recent interference experiments involving multiple photons are reviewed. These experiments include generalized photon bunching effects, generalized Hong-Ou-Mandel interference effects and multi-photon interferometry for demonstrations of multi-photon de Broglie wavelength. The multi-photon states used in these experiments are from two pairs of photons in parametric down-conversion. We find that the size of the interference effect in these experiments, characterized by the visibility of the interference pattern, is governed by the degree of distinguishability among different pairs of photons. Based on this discovery, we generalize the concept of multi-photon temporal distinguishability and relate it to a number of multi-photon interference effects. Finally, we make an attempt to interpret the coherence theory by multi-photon interference via the concept of temporal distinguishability of photons.

Fifty years ago, Yang and I worked on the dilute hard-sphere Bose gas, which has been experimentally realized only relatively recently. I recount the background of that work, subsequent developments, and fresh understanding. In the original work, we had to rearrange the perturbation series, which was equivalent to the Bogoliubov transformation. A deeper reason for the rearrangement has been a puzzle. I can now explain it as a crossover from ideal gas to interacting gas behavior, a phenonmenon arising from Bose statistics. The crossover region is infinitesimally small for a macroscopic system, and thus unobservable. However, it is experimentally relevant in mesoscopic systems, such as a Bose gas trapped in an external potential, or on an optical lattice.

In this work, we present an extensive theoretical analysis of nonlinear optical waveguide sensor. The waveguide under consideration consists of a thin dielectrica film surrounded by a self-focused nonlinear cladding and a linear substrate. The nonlinearity of the cladding is considered to be of Kerr-type. Both cases, when the effective refractive index is greater and when it is smaller than the index of the guiding layer, are discussed. The sensitivity of the effective refractive index to any change in the cladding index in evanescent optical waveguide sensor is derived for TM modes. Closed form analytical expressions and normalized charts are given to provide the conditions required for the sensor to exhibit its maximum sensitivity. The results are compared with those of the well-known linear evanescent waveguide sensors.

The ground state structures of Co₁₂X(X=Ni, Ag, Pt, Au) clusters are obtained by a genetic algorithm with a Gupta-like many-body potential, and further optimized using the density functional theory with generalized gradient approximation. The structures of Co₁₂X have a slightly distorted icosahedral pattern. The X atom is on the surface for the most stable configuration. Their total magnetic moments are 0μ_B, 3μ_B, 21μ_B, and 22μ_B, respectively. The reasons for the reduction of magnetism of Co₁₂X are discussed in detail.

The donor/acceptor heterojunction devices having configuration n-PANI/p-PSi were fabricated by in-situ chemical oxidative polymerization method of aniline on p-type porous silicon. The structure of n-PANI/p-PSi junctions was examined by scanning electron microscopy and X-ray diffraction spectroscopy. The dark current-voltage measurements were performed in the temperature range of 303–393 K to determine the electrical transport mechanisms of these devices. Rectifying properties were obtained and capacitance–voltage at 1 MHz behavior indicates an abrupt interface. At low forward bias, the current was found to be limited by thermionic emission of holes from p-PSi over the PANI/PSi barrier in the PANI thin film. For relatively higher voltage, the conduction was dominated by a space charge limited current mechanism, with an exponential distribution of traps. Also, various electrical parameters were determined from the I-V and C-V analysis.

We consider a graphene sheet folded in an arbitrary geometry, compact or with nanotube-like open boundaries. In the continuous limit, the Hamiltonian takes the form of the Dirac operator, which provides a good description of the low energy spectrum of the lattice system. We derive an index theorem that relates the zero energy modes of the graphene sheet with the topology of the lattice. The result coincides with analytical and numerical studies for the known cases of fullerene molecules and carbon nanotubes, and it extends to more complicated molecules. Potential applications to topological quantum computation are discussed.

The motivation of this work raises four challenging questions: (1) Why is it that so many generalized random network models exist but they cannot be completely consistent with real-world networks? (2) Are these complex networks fundamentally attached in a random preferential manner without any deterministic attachment for both un-weighted and weighted networks? To answer the first two questions, we propose a harmonious unifying hybrid preferential model (HUHPM) controlled by a total hybrid ratio. (3) Why are social networks mostly positive degree-degree correlation but biological and technological networks tend to possess negative degree-degree correlation? (4) Are there coherent physical ideas and a unification formation mechanism for studies of complex networks? To seek a better answer of all these questions, especially the last two above, we extend the HUHPM to a large unifying hybrid network model (LUHNM), based on introducing two new hybrid ratios. We study the two models above, both numerically and analytically. All findings of topological properties in the network models above can give a certain universally meaningful result, which reveals some nontrivial topological properties, new phenomena, and give a relatively satisfactory answer.

In this contribution, a three level atom in interaction with a two-mode quantized electromagnetic field, initially prepared in an entangled two-mode coherent state, is considered. Through the elimination of an intermediate level using the adiabatic elimination method, a nonlinear Stark shift is introduced. The exact solution of the wave function in the Schrödinger picture is obtained. Some statistical aspects through the effective two-level atom interacting with the two-mode and multiphotons processess with the nonlinear Stark shift are presented. The results are employed to perform a careful investigation of the temporal evolution of the atomic inversion, entropy squeezing and variance squeezing. It has been shown that the system is sensitive to any change in the parameter representation of the Stark shift. General conclusions reached are illustrated by numerical results.

Chaotic dynamics of fractional (non-integer) order systems have begun to attract much attention in recent years. In this paper, we study the phase and lag synchronization in coupled two fractional order chaotic oscillators. It is shown that with the increase of coupling strength, the system first undergoes a transition to phase synchronization, and when the coupling strength is increased further, another transition to lag synchronization occurs. It is further shown that the system with two chaotic oscillators of different orders can also exhibit phase synchronization phenomena, although the identical synchronization is impossible in this case.