Polarization Properties of Quantum-Dot-Based Single Photon Sources

Polarization properties of single photons emitted by optical pumping from a single quantum dot （ QD） are studied by using a four-level system model. The model is capable of explaining the polarization uncertainty observed in single photon emission experiments. It is found that the dependence of photon emission efficiency and polarization visibility on pump power are opposite in general cases. By employing QDs with small size and strong carrier confinement, the photon polarization visibility under high pump power can be improved. In addition, embedding a QD into a well designed microcavity is also found to be favourable, whereas the trade-off between high polarization visibility and multi-photon emission is noted.     

Entanglement of Momentum for a Single Photon with a Single Atom

In this talk, the interaction of a single photon injected to a single atom is studied, for which initially the photon is uncorrelated with the atom. The spontaneous emitted photon will then evolve to be entangled with the atom on their continuous kinetic variables （momentum） in the process of resonant scattering. We find the relations between the entanglement and their physical control parameters （such as the linewidth of the injected photon wave packet, and that of the atomic wave packet, etc. ）, which indicates that high entanglement can be reached by broadening the scale of the atomic wave or squeezing the linewidth of the incident single-photon pulse.     

Photon Statistics of Single-Photon Quantum States in Real Single Photon Detection

Single photon detection (SPD) with high quantum efficiency has been widely used for measurement of different quantum states with different photon distributions.Based on the direct single SPD and double-SPD of HBT configuration, we discuss the effect of a real SPD on the photon statistics measurement and it shows that the measured photon distributions for different quantum states are corrected in different forms.The results are confirmed by experiment with the strongly attenuated coherent light and thermal light.This system can be used to characterize the photon statistics of the fluorescence light from single atom or single molecular.     

Trichromatic Manipulation of Kerr Nonlinearity in a Three-Level Λ Atomic System

Trichromatic manipulation of Kerr nonlinearity in a three-level ∧ atomic configuration is investigated theoretically. It is Shown that for a weak monochromatic probe field, the enhanced Kerr nonlinearity can be achieved in multiple separate transparent windows due to interference effect of multiple two-photon Raman channels. Furthermore, the property of Kerr nonlinearity can be controlled by the sum of the relative phases of the sideband components of the trichromatic pump field compared to the central component.     

Preparation of the W State of Atoms in a Single Cavity or N Distant Cavities by Photon Interference

We suggest two schemes to generate the W state of N A-type three-level atoms. In the schemes, identical N three-level atoms are trapped in a cavity or N distant cavities. The success or failure of the generation of the W state can be determined by detecting the polarization of photon leaking out of the cavity. The result demonstrates that the W state is free from both the cavity loss and the spontaneous emission due to the fact that the two ground states (left and right) of the three-level atoms are stable states (or metastable states).     

Trapping State in a System of Single Three-level Trapped Ion Driven by External Fields

We investigate the interaction of a single three-level trapped ion with two laser beams. By applying a unitary transformation and a small rotating transformation, an exact solution to this quantum system is obtained without performing the Lamb-Dicke approximation, and the trapping state is observed.     

Photon Radiation Induced by Multiple Parton Rescattering in Deeply Inelastic Scattering

Photon radiation induced by multiple parton rescattering and corresponding parton energy loss in eA deeply inelastic scattering are investigated by using the generalized factorization of higher twist parton distributions beyond the helicity amplitude approximation.It turns out that the behaviour fo the nuclear size dependence of the parton energy loss is different in the photon and gluon radiation cases.The parton energy loss due to photon radiation depends linearly,instead of quadratically,on nuclear size due to gluon radiation.     

Exploration for Degradation of Λ Polarization Produced in Relativistic Nucleus Nucleus Collisions

The degradation of Λ transverse polarization produced in S+Pb central collisions at energy 200 GeV per nucleon has been studied in detail. The S+Pb central collision events have been generated using Monte-Carlo generator——LUCIAE at 200 GeV per nucleon. The various factors degrading Λ transverse polarization have been analysed quantitatively. The ratios of Λ′s produced from rescattering, secondary production and decays of Σ, Ξ hyperons to the total measurable Λ′s in experiment have been investigeted and the degradation effect of these Λ on the total polarization has been determined. The simulation and calculation show that above three factors decrease the Λ transverse polarization strongly, however, can not eliminate the polarization completely when the Λ′s are assumed to be produced from hadronic gas in the final state. To explan the experimental data of vanished Λ polarization, it probably needs to consider new mechanisms of Λ production, including a weak effect of QGP formation.     

Coherent Scattering of Light by Bose-Einstein Condensation in a Tight Confinement

We have observed strong scattering of a probe light by dilute Bose-Einstein condensate （BEC） ^87Rb gas in a tight magnetic trap. The scattering light forms fringes at the image plane. It is found that we can infer the real size of the condensation and the number of the atoms by modelling the imaging system. We present a quantitative calculation of light scattering by the condensed atoms. The calculation shows that the experimental results agree well with the prediction of the generalized diffraction theory, and thus we can directly observe the phase transition of BEC in a tight trap.     

Second-Order Correlation Function of the Photon Emission from a Single Quantum Dot

The photon correlation of photon emission from a single quantum dot with cw excitation and pulsed excitation is investigated in details. To calculate the second-order correlation function for optical pumping, we deduce rate equations with a simplified two-level model under cw excitation and present the master equation approach in the interaction picture to the study of evolution of a three-level system under pulsed excitation. In addition, we report photon correlation measurements on a single self-assembled In0.5Ga0.5As quantum dot, which show strong antibunching behaviour under both the conditions of cw and pulsed excitations. The calculated results are in agreement with the experimental measurements.     

Phase Dependence of the Inversionless Gain in a Λ System with Near—Degenerate Levels

Due to interaction with the vacuum of the radiation field,near-degenerate lower levels in a Λ system have an additional coherence term,the spontaneously generated coherence (SGC) term.For such a system,we investigate the effect of the relative phase between two coherent fields on the inversionless gain in the presence of the SGC.We find that the inversionless gain,which stems from both SGC and dynamically induced coherence,can be modulated by the relative phase.     

Adiabatic Raman passage via two-photon resonant transitions in a five-level Λ system

We investigate a five-level Λ system for achieving the efficient population transfer between two ground-state levels without essentially populating other three intermediate excited-state levels. This five-level Λ system is found to have an approximate dark state characterized by very small (but not exactly zero) absolute eigen-values when we work in the parameter regime where all single-photon pump and Stokes transitions are well suppressed. Dynamically manipulating the approximate dark state in a proper way, we can either attain the complete population transfer from one ground-state level to another ground-state level or create the maximal coherence between the two ground-state levels. The dynamic process of a stimulated Raman adiabatic passage is implemented in fact by manipulating a two-photon resonant pump transition and a two-photon resonant Stokes transition, which is especially important when the two ground-state levels differ by Δm = ± 4 in the magnetic quantum number.     

Physics and Chemistry in Laser—Trapped Single Microparticles Studied by Light Scattering

In this lecture various physical and chemical aspects are discussed when single particles of the size of the faserwavelength are trapped in strongly focused laser beams.First,we describe varius possibilities for the trapping techniques and micro-Raman setups.Then we discuss Raman-Mie-scattering and morphology dependent resonances which occur in dielectric spherical microparticles.These particles react as microresonators and influence the Raman spectra senerating input and output resonances.The electric field distribution inside and outside the dielectric microsphere in and out of resonance have been calcuated quantitatively to explain the input resonances.We also report on observed fast temperature jumps when microdroplets undergo an input resonance.Applications of these combined inelastic/elastic light scattring studies will be shown for microdroplet evaporation and for chemical studies such as simple acid/base reactions in a microdroplet,Furthermore we show results of recent studies on the emulsion polymerization process of styrene by applying a gradient force trap in a microscope.     

Excitation of Electromagnetic Waves by an Electron Ring Beam in a Magnetized Plasma Waveguide

We study the resonant interactions between an electron ring beam and plasma waveguide modes,This is motivated by the research of radio emission in low solar corona.We consider a density-depleted duct(above an active region near a flare site)that may be treated as a magnetized plasma waveguide.The electromagnetic waves excited in the wveguide are classified into the so-called E-type and B-type waves.The results show that there are two unstable modes of B-type waves propagating parallel and anti-parallel to the direction of the electron beam.The effect of the finite radius and boundary conditions of the waveguide on the excitation of the electron beam.The effect of the finite radius and oundary conditions of the waveguide on the excitation of waveguide modes is important.For a given B-type mode,the smaller the radius R,the larger the temporal and spatial amplification important.For a given B-type mode.the smaller the radius R ,the larger the temporal and spatial amplification rate,we suggest that these excited waveguide modes could be one of the processes respondsible for the observed solar radio emission.     

Frequency Dependence of Polarization Mode Dispersion in a Crystal-Based Polarization Mode Dispersion Compensator

We report the frequency dependence of polarization mode dispersion (PMD) in a PMD compensator based on six cascaded birefringent crystals separated by Faraday rotators. When all crystal axes are aligned, the device can compensate for the first-order PMD. However, if all crystal axes are coupled with arbitrary angles, it can compensate for high-order PMD. The variations of differential group delay and principal state of polarization with optical frequency are analysed. The PMD vector and Stokes components of the device versus wavelength are measured. The theoretical simulations agree well with the experimental results.     

Eigenstates of Laser-Assisted Scattering in a Noninertial Frame

In a rotating noninertial frame, we investigate the eigenstates of the time-dependent problem for electronnucleus scattering assisted by a circularly polarized laser field. Numerical results of probability distribution, quantum potential, and current density are discussed. An approximate expression of scattering cross section for low laser frequency is given.     

Sedimentation of a Single Charged Elliptic Cylinder in a Newtonian Fluid by Lattice Boltzmann Method

We simulate the sedimentation of single charged and single uncharged elliptic cylinders in a Newtonian fluid byusing the lattice Boltzmann method. Due to the polarizing effects and non-axial symmetry shape, there are theCoulomb force and corresponding torque exerted on the charged elliptic cylinder during the sedimentation, whichsignificantly change the horizontal translation and rotation of the cylinder. When the dielectric constant of theliquid is smaller than that of the wall, the direction of the Coulomb force is opposite to that of the hydrodynamicforce. Therefore there appears to be a critical linear charge density qc at which the elliptic cylinder will fallvertically off the centreline.     

Competition between Quantum Interference and Stimulated Electronic Raman Scattering Processes via Hybrid Excitation in a Na_2-Na System

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Pure Reflection and Refraction of a Surface Polariton by a Matched Waveguide Structure

We study the fundamental problem of reflection and refraction of a surface polariton as it strikes the interface between two waveguide structures. By making the two waveguide structures match to each other, coupling of surface polaritons to radiating modes is cancelled, and the reflected and transmitted waves consist of only surface modes. The reflection and transmission coefficients are calculated, and negative refraction of surface polaritons is demonstrated. Finite-difference time-domain numerical simulations are also performed to verify the analytical results. As one of the applications of the matched waveguide structure, a square corner reflector for phase-retardation-free reflection of surface polaritons is proposed.