Optical field-strength generalized polarization of multimode single photon states in integrated directional couplers

A quantum analysis of the generalized polarization properties of multimode single photon states is presented. It is based on the optical field-strength probability distributions in such a way that generalized polarization is understood as a significant confinement of the probability distribution along certain regions of the multidimensional optical field-strength space. The analysis is addressed to multimode integrated waveguiding devices, such as N?×?N integrated directional couplers, whose modes fulfil a spatial modal orthogonality relationship. For that purpose a definition of the quantum generalized polarization degree in a N-dimensional space, based on the concept of distance to an unpolarized N-dimensional Gaussian distribution, is proposed. The generalized polarization degree of pure and mixture multimode single photon states and also of some multi-photon states such as coherent and chaotic ones, is evaluated and analyzed.     

Spin operator for quantum light in integrated photonic waveguides

In this work a quantum mechanical derivation of the Spin operator in integrated isotropic and anisotropic photonic waveguides is obtained from both first principles of the electromagnetic theory and conservation laws, and moreover, within a phenomenological quantization approach. The Spin operator will be derived by starting from the spin conservation law to obtain the spin flux density and by means of a quantization based on the vector structure and orthonormality property of guided modes; likewise, since anisotropic guides produce polarization changes, and consequently changes of the expected values of spin, we will also present the Momentum operator for anisotropic guides. The expression for the Spin angular momentum operator shows that both the presence of modal longitudinal components and the modal mismatching reduces the spin values, but it comes into the standard expression when it is used in homogeneous media and in particular with uniform and infinite plane modes. Likewise these results have a direct influence on the Stokes's operators which allow one to analyze quantum polarization in integrated photonics.     

Alignment and optical polarization of InGaAs quantum wires on GaAs high index surfaces

Highly ordered three-dimensional periodic arrays of In_0.40Ga_0.60As quantum wires (QWRs) on GaAs (311)A and GaAs (331)A have been achieved by molecular beam epitaxy and revealed by high-resolution X-ray diffraction. Polarization dependent photoluminescence measurements demonstrated high optical anisotropy of 40% in (331)A QWRs and 16% in (311)A QWRs. Such a difference in polarization value could be caused by the differences in geometry, ordering, and high piezoelectric field between (331)A and (311)A samples.     

应变GaN量子点中激子态的研究

利用有效质量方法和变分原理,考虑内建电场效应和量子点的三维约束效应,研究了约束在GaN/AlxGa1-xN圆柱形量子点中的激子特性与量子点的结构参数以及势垒层中Al含量之间的关系.结果表明:对给定大小的量子点,随其高度的增加激子结合能出现一最大值,此时载流子被最有效的约束在量子点内;内建电场使量子点的有效带隙减小,电子、空穴产生明显分离,从而影响量子点的光学性质.理论计算的光跃迁能和实验结果一致.     

Light polarization states of a cholesteric liquid crystal probed with optical ellipsometry

Herein a useful methodology to study optical properties of cholesteric liquid crystals (Ch-LC) is proposed by using the Fourier decomposition ellipsometry technique to calculate the Stokes parameters of transmitted and reflected light in the UV–Vis spectral range. Combining Bragg reflection and optical activity we were able to obtain ∼100% of linear or circular light polarization from the Ch-LC sample using achromatic and non-polarized light source. The photonic bandgap and the polarization components can be controlled with the temperature as a result of alterations in the helix pitch of the cholesteric phase. Finally, it is demonstrated the correlation between the dissymmetry factor (g) calculated via the Stokes parameter S₃ and the reflection spectrum. The data revealed that the maximum value of S₃ is not coincident with the peak of maximum reflection. The reflected or transmitted light analysis via Stokes parameters obtained by ellipsometry showed an alternative and low cost method for optical characterization in Ch-LC.     

光子晶体在Si基发光器件中的应用

在Si基集成光电子学的发展中,实现高效的Si基光源始终是人们期待的目标.但是Si材料的间接带隙特性导致其发光效率低.目前,已经探索了多种Si基材料体系以提高Si材料的发光效率,但是尚未取得突破性的进展.近年来,光子晶体以其独特的控光能力而备受人们的关注,将光子晶体引入到Si基材料体系中可以显著提高Si基材料的发光效率,这无疑对Si基光电子学的发展起到了重要的贡献.本文简述了利用光子晶体提高Si基材料发光效率的机制,介绍了光子晶体在几种Si基材料中的应用,探索了Si基光子晶体发光器件的潜在应用前景.     

Multimode polarization degree of mixture optical states in integrated directional couplers

Mixture multimode optical field classical states propagating in N?×?N integrated directional couplers are analyzed by using the density matrix formalism in a N-dimensional optical space. These mutimode optical fields present a kind of generalized polarization and accordingly a definition of a multimode polarization degree is proposed. It is based on the distance measure between a mixture state and an unpolarized state in a N-dimensional optical space so that in the case N=2 the standard polarization degree is recovered. It is shown that directional couplers can reduce or increase remarkably the multimode polarization degree of a mixture state. Likewise a simple measurement technique, based on Y junctions, of this multimode polarization degree is proposed. Finally all the results can be formally extended to the special case of multimode single photon quantum states.     

Electrical and optical control of entanglement entropy in a coupled triple quantum dot system

We investigated theoretically the entanglement creation through tunneling rate and fields in a four-level triple quantum dot molecule based on InAs/GaAs/AlGaAs heterostructure in both steady state and transient state. We demonstrate that the entanglement entropy among the QDM and its spontaneous emission fields can be controlled by coherent and incoherent pumping field and tunnel-coupled electronics levels. The results may provide some new possibilities for technological applications in solid-state quantum information science, quantum computing, teleportation, encryption, compression codec, and optoelectronics.     

Restoration of polarization in ferroelectric thin films studied with the model of trapping of carriers at interfacial states

A model based on trapping and releasing of free carriers in band gap states located at the interfaces between electrodes and the ferroelectric film is used to explain the restoration of polarization which is sometimes observed. Experimental data on two kinds of polarization restoration in metal/ferroelectric/metal thin film structures are reported. The increase of polarization, which may be observed at the early stage of fatigue test, is attributed to the release of carriers which are trapped in interfacial states at the virgin state, before fatigue test. On the other hand, the previously reported “self recovery effect” is attributed to a competition between the strength of a trapped carrier-ferroelectric dipole interaction and the applied voltage which acts on the dipole orientation.     

Electronic energy transfer between long-range resonance states of 3-mercaptopropionic acid capped CdTe quantum dots in aqueous media

We demonstrate electronic energy transfer between resonance states of 2 and 2.8?nm CdTe quantum dots in aqueous media using steady-state photoluminescence spectroscopy without using any external linker molecule. With increasing concentration of larger dots, there is subsequent quenching of luminescence in smaller dots accompanied by the enhancement of luminescence in larger dots. Our experimental evidence suggests that there is long-range resonance energy transfer among electronic excitations, specifically from the electronically confined states of the smaller dots to the higher excited states of the larger dots.     

Optical investigation of quantum confinement in PbSe nanocrystals at different points in the Brillouin zone

We present detailed investigations on the optical properties of PbSe nanocrystals. The absorption spectra of monodisperse, quasispherical nanocrystals exhibit sharp features as a result of distinct optical transitions. To study the size dependence, absorption spectra of nanocrystals ranging from 3.4 to 10.9 nm in diameter are analysed and a total of 11 distinct optical transitions are identified. The assignment of the various optical transitions is discussed and compared to theoretically calculated transition energies. By plotting all transitions as a function of nanocrystal size (D) we find that the energy (E) changes with the following relationship [Formula: see text] for the lowest energy transitions. The transition energy extrapolates to approximately 0.3 eV for infinite crystal size, in agreement with the bandgap of bulk PbSe at the L-point in the Brillouin zone. In addition, high-energy transitions are observed, which extrapolate to 1.6 eV for infinite crystal size, which is in good agreement with the bulk bandgap of PbSe at the Sigma-point in the Brillouin zone. Tight-binding calculations confirm that the high-energy transitions originate from the Sigma-point in the Brillouin zone. The Sigma-character of the high-energy transitions may be of importance to explain the mechanism behind multiple exciton generation in PbSe nanocrystals.     

Proposal for measuring the quantum states of neutrons in the gravitational field with a CCD-based pixel sensor

An experimental setup is proposed for the precise measurement of the quantum states of ultracold neutrons bound in the earth's gravitational field. The experiment utilizes a CCD-based pixel sensor and magnification system to observe the fine structure of the neutron distribution. In this work, we analyzed the sensor's deposited energy measurement capability and found that its spatial resolution was . A magnifying power of two orders of magnitude was realized by using a cylindrical rod as a convex mirror.     

Enhancement of evanescent field exposure in a photonic crystal fibre with interstitial holes

In this work, a modified photonic crystal fibre (PCF) that we refer to as Sunny PCF with enhanced evanescent field exposure structure is proposed. The Sunny PCF with triangular interstitial air holes surrounding the core region increases the interaction of the guided mode with the air. Full-vectorial finite element method with perfectly matched layer boundary condition is used to design and simulate the sensitivity and confinement loss characteristics of the proposed Sunny PCF. By adding sunny structure to a conventional PCF with air-filling ratio of 0.9, the highest achievable sensitivity with negligible confinement loss can be boosted up to 21.23% from 15.83% at the operating wavelength of 1550 nm. Sunny PCF can achieve the same sensitivity as suspended-core holey fibre with lower confinement loss. A preliminary Sunny PCF has been fabricated to prove the feasibility of the proposed structure.     

Time evolution of entanglement and bistability of two coupled quantum dots in a driven cavity

Abstract

The time evolution of entanglement between two quantum dots (QDs) trapped inside a cavity driven by a coherent quantized field is studied. In the presence of dissipation, entanglement shows many interesting features such as sudden death and revival, and finite steady state value after sudden death. We also investigate dependence of entanglement on dot variables and its relation to bistability. It is found that entanglement vanishes when the cavity field intensity approaches the upper branch of the bistability curve. When the cavity is driven by a modulated field in the presence of dissipation, it can periodically generate entanglement, which is much larger than the maximum value attained in the steady-state for this system but the dots are never fully entangled.     

A quantum description of linear,and non-linear optical interactions in arrays of plasmonic nanoparticles

A quantum theory for describing the interaction of photons and plasmons, in one- and two-dimensional arrays is presented. Ohmic losses and inter-band transitions are not considered. We use macroscopic approach, and quantum field theory methods including S-matrix expansion, and Feynman diagrams for this purpose. Non-linear interactions are also studied, and increasing the probability of such interactions, and its application are also discussed.     

Magnetocrystalline anisotropy energy and spin polarization of Fe3Si in bulk and on Si(001) and Si(111) substrates

In order to achieve highly efficient spin polarized transport, first of all magnetocrystalline anisotropy energy, which determines the magnetic easy axis, must be understood. The highly precise full-potential linearized augmented plane-wave method is employed to investigate the magnetism and magnetocrystalline anisotropy energy of a ferromagnetic Heusler alloy Fe₃Si on Si(001) and Si(111) substrates. The calculated magnetocrystalline anisotropy energy of bulk D0₃ Fe₃Si was found to depend sensitively on a tetragonal distortion: The magnetization is along the z-axis at c/a < 1 and on the xy plane at c/a > 1. The out-of-plane magnetic easy axis of both Fe₃Si/Si(001) and (111) was calculated to be quite stable with enhanced magnetocrystalline anisotropy energy compared with bulk value. The magnetic easy axis of Fe₃Si/Si(001) and (111) is discussed in detail with single particle energy spectra. The degree of spin polarization is also presented at the interfaces between Fe₃Si and Si. The calculated spin polarizations of Fe₃Si/Si(111) tend to retain the spin polarization of the bulk, whereas they are reduced for the (001) interfaces.