arXiv subjects

Ying Wu

Publications and source records attributed to Ying Wu.

152 records · Page 9Linked to original sources

arXiv2013

Semi-Dirac dispersion relation in photonic crystals

A semi-Dirac cone refers to a peculiar type of dispersion relation that is linear along the symmetry line but quadratic in the perpendicular direction. Here, I demonstrate that a photonic crystal consisting of a square array of elliptical dielectric cylinders is able to produce this particular dispersion relation in the Brillouin zone center. A perturbation method is used to evaluate the linear slope and to affirm that the dispersion relation is a semi-Dirac type. Effective medium parameters calculated from a boundary effective medium theory not only explain the unexpected topological transition in the iso-frequency surfaces occurring at the semi-Dirac point, they also offer a perspective on the property at that point, where the photonic crystal behaves as a zero-refractive-index material along the symmetry axis but functions like at a photonic band edge in the perpendicular direction.

physics.optics↗

arXiv2012

Quantum-criticality-induced strong Kerr nonlinearities in optomechanical systems

We investigate a hybrid electro-optomechanical system that allows us to obtain controllable strong Kerr nonlinearities in the weak-coupling regime. We show that when the controllable electromechanical subsystem is close to its quantum critical point, strong photon-photon interactions can be generated by adjusting the intensity (or frequency) of the microwave driving field. Nonlinear optical phenomena, such as the appearance of the photon blockade and the generation of nonclassical states (e.g., Schrödinger cat states), are predicted in the weak-coupling regime, which is feasible for most current optomechanical experiments.

quant-ph↗

arXiv2012

A Lumped Model for Rotational Modes in Phononic Crystals

We present a lumped model for the rotational modes induced by the rotational motion of individual scatterers in two-dimensional phononic crystals comprised of square arrays of solid cylindrical scatterers in solid hosts. The model provides a physical interpretation of the origin of the rotational modes, reveals the important role played by the rotational motion in the band structure, and reproduces the dispersion relations. The model increases the possibilities of wave manipulation in phononic crystals. In particular, expressions, derived from the model, for eigen-frequencies at high symmetry points unambiguously predict the presence of a new type of Dirac-like cone at the Brillouin center, which is found to be the result of accidental degeneracy of the rotational and dipolar modes.

cond-mat.mtrl-sci↗

arXiv2012

Do Linear Dispersions of Classical Waves Mean Dirac Cones?

By using the \vec{k}\cdot\vec{p} method, we propose a first-principles theory to study the linear dispersions in phononic and photonic crystals. The theory reveals that only those linear dispersions created by doubly-degenerate states can be described by a reduced Hamiltonian that can be mapped into the Dirac Hamiltonian and possess a Berry phase of -π. Triply-degenerate states can also generate Dirac-like cone dispersions, but the wavefunctions transform like a spin-1 particle and the Berry phase is zero. Our theory is capable of predicting accurately the linear slopes of Dirac/Dirac-like cones at various symmetry points in a Brilliouin zone, independent of frequency and lattice structure.

cond-mat.mtrl-sci↗

arXiv2011

Elastic metamaterials with simultaneously negative effective shear modulus and mass density

We propose a type of elastic metamaterial comprising fluid-solid composite inclusions which can possess negative shear modulus and negative mass density over a large frequency region. Such a solid metamaterial has a unique elastic property that only transverse waves can propagate with a negative dispersion while longitudinal waves are forbidden. This leads to many interesting phenomena such as negative refraction, which is demonstrated by using a wedge sample, and a significant amount of mode conversion from transverse waves to longitudinal waves that cannot occur on the interface of two natural solids.

cond-mat.mtrl-sci↗

arXiv2009

Dispersion Relations and Their Symmetry Properties for Electromagnetic and Elastic Metamaterials in Two Dimensions

In the framework of multiple-scattering theory, we show that the dispersion relations of certain electromagnetic (EM) and elastic metamaterials can be obtained analytically in the long-wavelength limit. Specific examples are given to the two-dimensional metamaterials with cylindrical inclusions arranged in square and triangular lattices. The role played by the lattice structure in determining whether a dispersion relation is isotropic or not is shown explicitly. Different lattice dependences between EM and elastic metamaterials are also shown. In the case of isotropic dispersions, our results coincide with those of isotropic effective medium theories obtained previously for EM and elastic metamaterials, respectively, and, therefore, provide a more fundamental support to those theories. In the case of elastic metamaterials with anisotropic dispersions, our analytical results can provide an anisotropic effective medium theory in the form of Christoffel's equation. In this case, the isotropic effective medium theory can describe accurately the angle-averaged dispersion relations. The properties of anisotropic dispersions are discussed and verified by numerical calculations of a realistic elastic metamaterial.

cond-mat.mtrl-sci↗

arXiv2007

A Dynamical Effective Medium Theory for Elastic Metamaterials

We develop a dynamical effective medium theory to accurately predict the unusual properties of elastic metamaterials in two dimensions near the resonant frequencies. The theory shows that the effective bulk modulus, shear modulus, and mass density can be made negative by choosing proper resonant scatterers, leading to 8 possible types of wave propagation. The theory not only provides a convenient tool to search for various metamaterials with desired properties, but also gives a unified physical picture of these properties. Here we demonstrate two examples. One possesses large band gaps at low frequencies. The other exhibits two regions of negative refraction: one for both longitudinal and transverse waves and the other for longitudinal waves only.

cond-mat.mtrl-sci↗

arXiv2002

N-qubit Entanglement Index and Classification

We show that all the N-qubit states can be classified as N entanglement classes each of which has an entanglement index $E=N-p=0,1,...,N-1$(E=0 corresponds to a fully separate class) where $p$ denotes number of groups for a partition of the positive integer N. In other words, for any partition $(n_1,n_2,...,n_p)$ of N with $n_j\ge 1$ and $N=\sum_{j=1}^{p}n_j$, the entanglement index for the corresponding state $ρ_{n_1}\bigotimesρ_{n_2}...\bigotimes ρ_{n_p}$ with $ρ_{n_j}$ denoting a fully entangled state of $n_j-$qubits is $E(ρ_{n_1}\bigotimesρ_{n_2}...\bigotimes ρ_{n_p})=\sum_{j=1}^{p}(n_j-1)=N-p$.

quant-ph↗