Dissertation > Excellent graduate degree dissertation topics show
Investigations on Landau Damping of Collective Excitations in BoseEinstein Condensates
Author: MaXiaoDong
Tutor: HuangGuoXiang
School: East China Normal University
Course: Optics
Keywords: BoseEinstein condensation collective excitations HartreeFockBogoliubov theory ThomasFermi approximation variation wavefunction threemode coupling matrix elements Landau damping
CLC: O414.2
Type: PhD thesis
Year: 2007
Downloads: 167
Quote: 0
Read: Download Dissertation
Abstract
BoseEinstein Condensation （BEC） is a phenomenon of macroscopic occupation in one or several quantum states by a large number of identical bosons when the temperature of system is below to a critical temperature. BEC is one of the most basic conclusions in quantum statistic mechanics and the physical origin of many kinds of macroscopic quantum phenomena. BEC theory is also the foundation of superconductivity and superfluidity. The research of BEC is the cross point of many disciplines, including atom and molecular physics, nonlinear and quantum optics, statistical physics and condensed matter physics, and hence has significant importance from the theoretical viewpoint. On the other hand, the study of BEC has also promising future prospects in practical applications, including designing atom laser and increasing largely the measurement precision for fundamental physical quantities.The research of elementary excitations is one of the basic topics in statistical physics and condensed matter physics. Collective excitations are the most basic excitation modes in BEC at low temperature. The study of collective excitations is very important for understanding the properties of ground state, superfluidity and thermodynamics of BECs. The interparticle interaction results in not only the generation ofcollective excitations, but also the decay of their amplitudes （called as damping） and the shift of their oscillating frequencies. For the bosons trapped in a potential, a collectivemode amplitude decays with respect to time via mainly the mechanics of Landau damping, i. e. a quasiparticle absorbs the collective mode and then transferred into a new quasiparticle. Landau damping is the most basic phenomenon in trapped BEC and its precision calculation may be used to explain many experimental phenomena, and test and develop the quantum manybody theory for condensed matter. The precision measurement of Landau damping can also be inversely used to deduce the interparticle interaction and superfluid property of the system. Although there exist a lot of studies on the Landau damping of collective excitations in trapped BECs made by many famous laboratories and theoretical groups in the world, however, there is still no satisfactory theoretical explanation on the experimental results up to now.In this thesis, we have developed a new, systematic analytical method for making a thorough study on the Landau damping of collective excitations in BECs. The main research results are listed below:1. We have studied the Landau damping of the lowest breathing mode in the BEC of a ^{87}Rb atomic gas trapped in a spherical symmetric （anisotropy parameter λ=1） harmonic potential. By using a improved ThomasFermi approximation we have obtained the ground state wavefunction of the condensate. Based on this we have solved Bogoliubovde Gennes equations satisfied by collective excitations and quasiparticles and obtained the analytical solutions of divergencefree Bogoliubov amplitudes andcoupling matrix elements describing the interaction among collective excitations and quasiparticles. Utilizing these analytical results we have calculated the Landau damping of the breathing mode based on the timedependent HatreeFockBogoliubov meanfield theory. The result has been compared with numerical simulation and found a good agreement.2. Based on the timedependent HatreeFockBogoliubov meanfield theory we have constructed and developed a general theoretical method for studying the Landau damping of collective modes in anisotropic BECs. Bymeans of this method we have investigated the Landau damping of ω_{} modein the BEC of a ^{87}Rb atomic gas trapped in an anisotropic (λ =8^{1/2}) potential.We have calculated coupling matrix elements of threemode interaction, damping strength and damping coefficient, and discussed the relations among the damping coefficient, temperature, particle number, and trapping frequencies. The calculating result agrees well with the experimental one.3. We have investigated the Landau damping of ω_{+} and ω_{} modes intrapped BEC of ^{87}Rb atomic gases for various anisotropic parameters A. We have calculated the threemode coupling matrix elements and damping strength, discussed the relations among the Landau damping coefficient, temperature, particle number and trapping frequencies. Our theoretical results are in agreement well with the experimental ones reported up to now.

Related Dissertations
 Study of Dynamical Effects of the Nucleusnucleus Potential Using the Quantum Molecular Dynamics Model,O571.6
 Single quantum well semiconductor medium plasmon properties of,O471.1
 Finite temperature BoseEinstein condensates impurities Casimir effect between classes,O431.2
 The Study of the Equation of State of Neutron Star Matter,P145.6
 Spectrum Analysis of Hydrogen Plasma at Low Temperature and Low Pressure,O536
 Capture the effect of the finite number of particles in the atom,O562
 Collective Excitations and Stability Analysis of Homogeneous TwoComponent Tonks Gas,O414.2
 The Propagation Characteristic of Waves in Quantum Plasmas,O534
 The Dielectric Function of Quarkgluon Plasma and Phenomena Induced by the Jet in the Medium,O572.33
 Theories of Geodesic Acoustic Modes in Tokamak Plasmas,O53
 Study on Some Basic Problems in Nonextensive Statistics,O212.1
 Dielectric and Dissipative Properties of Strong Interaction Matter,O572.2
 Quantum Dynamics of Bose Gas at Low Temperature,O413
 Experimental and Theoretical Investigations of Photoionization and Photodissociation Mechanisms of Cycloketones and Pyrrolidine Molecules,O561.4
 Interference of BoseEinstein Condensates in a Spindependent Optical Lattice and Tunneling Dynamics between Two Independent BoseEinstein Condensates,O431.2
 Theoretical Problems in Spinor BoseEinstein Condensation,O431.2
 The Study about the Thermodynamic Properties of Hadronic Matter and the Nonperturbative CJT Method,O572.2
 The Study on Giant Resonance Properties of Nucleus in a Relativistic Approach,O482.532
 Study of Interference of Cold Atom Beams,O431.2
 Investigations on Coherent Property and Nonlinear Effect of Superfluid Atomic Fermi Gases in the BCSBEC Crossover,O431.2
CLC: > Mathematical sciences and chemical > Physics > Theoretical Physics > Thermodynamics and Statistical Physics > Statistical physics
© 2012 www.DissertationTopic.Net Mobile
