Pseudogap phenomena in ultracold atomic Fermi gases

The pairing and superfluid phenomena in a two-component ultracold atomic Fermi gas is an analogue of Cooper pairing and superconductivity in an electron system, in particular, the high Tc superconductors. Owing to the various tunable parameters that have been made accessible experimentally in recent years, atomic Fermi gases can be explored as a prototype or quantum sinmlator of superconductors. It is hoped that, utilizing such an analogy, the study of atomic Fermi gases may shed light to the mysteries of high Tc superconductivity. One obstacle to the ultimate understand- ing of high Tc superconductivity, from day one of its discovery, is the anomalous yet widespread pseudogap phenomena, for which a consensus is yet to be reached within the physics comnnmity, after over 27 years of intensive research efforts. In this article, we shall review the progress in the study of pseudogap phenomena in atomic Fermi gases in terms of both theoretical understanding and experimental observations. We show that there is strong, unambiguous evidence for the existence of a pseudogap in strongly interacting Fermi gases. In this context, we shall present a pairing fuctuation theory of the pseudogap physics and show that it is indeed a strong candidate theory for high Tc superconductivity.     

Collective Excitations of Low Dimensional Trapped Bose-Condensed Gas

In this paper, we investigate excited characteristic of the weakly interacting quasi-one-dimensional (1D) and quasi-two-dimensional (2D) Bose-Einstein condensation (BEC) in harmonic potential trap. The energy spectrum and the analytical expression of the sound velocity are obtained and analyzed. Compared with 3-Dimensional homogeneous Bose-condensed gas occasion, the sound velocity of 2D Bose-Einstein condensation in harmonic potential trap is smaller.     

二维旋转简谐振子势的讨论

以二维旋转简谐振子势为例分析了在BEC中经常用到的旋转势,分析了哈密顿量的表达式,给出了波函数和能量本征值,并注意到了二维旋转简谐振子势与带电粒子在磁场中的情形具有相近的形式.     

Potential of Solid Sampling Electrothermal Vaporization for solving spectral interference in Inductively Coupled Plasma Optical Emission Spectrometry

Spectral interference is one of the main causes of erroneous results in Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). This paper describes some cases of spectral interferences with conventional nebulization ICP-OES and the potential of solving them utilizing electrothermal vaporization for volatility-based separation. The cases studied were, the well-known spectral overlap between the As and Cd lines at 228.8 nm that are only 10 pm apart, and the interference of Fe on the main emission lines of As, Cd and Pb. The spectral interferences were studied by monitoring the typical signals of solutions that contain the analytes and the potential interferent, by studying the spectra and calculating Background Equivalent Concentration (BEC)-values. A three step temperature program was developed to be used for direct analysis of solid soil samples by Electrothermal Vaporization (ETV)-ICP-OES: step 1 (760 °C, 40 s), step 2 (1620 °C, 20 s) and a cleaning step (2250 °C, 10 s) where Cd vaporizes in step 1, As, Pb and part of Fe in step 2 and the major part of Fe in the cleaning step. Because As and Cd were time-separated using this program, their prominent lines at 228.8 nm, could be used for determination of each element by ETV-ICP-OES, in spite of the serious wavelength overlap. Selective vaporization was also shown to reduce or eliminate the Fe background emission on As, Cd and Pb lines. To confirm the applicability of the method, a solid soil certified reference materials was analyzed directly without any sample treatment. Good or reasonable accuracy was obtained for the three elements.     

Magnetized vector solitons in a spin-orbit coupled spin-1 Bose-Einstein condensate with Zeeman coupling

The property of matter-wave vector solitons in a spin-1 Bose-Einstein condensate with spin-orbit and Zeeman couplings is investigated by multiscale perturbation method. The excitation spectrum and the corresponding state vectors of the system are obtained analytically, and they can be adjusted by the parameters of the system. The bright and dark vector solitons are formulated by reducing the three-component coupled Gross-Pitaeviskii equations to a standard nonlinear Schrödinger equation, which has the solutions of the bright and dark solitons with positive or negative mass depending on the product of the effective dispersive and nonlinear coefficients. The moving vector solitons are demonstrated by adjusting specific momentum near the energy minimum. Finally, the magnetized features of the vector solitons are discussed by the spin polarization of the system.     

Spontaneous U（1） Symmetry Breaking in Coupled Bose System

Adding a U(1) symmetry breaking term V^1/2 a(λ₁a₀+λ*₁a^†₀)+V^1/2(λ₂b₀+λ^*₂b^†₀) to Bogoliubov's truncated Hamiltonian H_B for a weakly interacting coupled Bose system, by using the mean-field approximation rather than the c-number approximation, we find that, via a Feshbach resonance at zero temperature, the states of the coupled Bose system are generalized SU(1,1) × SU(1,1) coherent states. The Bose-Einsteincondensation occurs in response to the spontaneous U(1) symmetry breaking.     

Micropillar resonator in a magnetic field: Zero and finite temperature cases

In this work, we present a theoretical study of a quantum dot–microcavity system which includes a constant magnetic field in the growth direction of the micropillar. First, we study the zero temperature case by means of a self-consistent procedure with a trial function composed of a coherent photon field and a BCS function for the electron–hole pairs. The dependence of the ground state energy on the magnetic field and the number of polaritons is found. We show that the magnetic field can be used as a control parameter for the photon number, and we make explicit the scaling of the total energy with the number of polaritons. Next, we study this problem at finite temperatures and obtain the scaling of the critical temperature with the number of polaritons.     

Time Evolution for Relative Phase of Two Bose-Einstein Condensates

Considering the collisions between the two condensates and the tunneling effects, we study the time evolution of the relative phase of two Bose-Einstein condensates (BECs). The phase amplitude is given in coherent picture for many cases, which furnishes us a new method to study the interference of two BECs.     

Critical temperature and condensed fraction of Bose-Einstein condensation in an external potential

Based on Bose-Einstein condensation at minimized momentum state, we get the expressions for the critical temperature and condensed fraction of Bose-Einstein condensation (BEC) in an external potential in the three-dimensional (3D) case. For the 1D and 2D cases, we present not only the critical temperature and corresponding particles but also the condition of BEC occurrence.