Browsing by Subject "Bose-Einstein condensation"
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Item Bose-Einstein condensation of dilute atomic gases(2001-08) Wu, Biao; Niu, QuianItem Controlling atomic motion: from single particle classical mechanics to many body quantum dynamics(2004) Hanssen, James Louis; Raizen, Mark G.This dissertation covers a series of experiments designed to control atomic motion. The experiments progress from being completely classical in nature to being described by many-body quantum mechanical models. The first experiment involves an experimental realization of a billiard using cold atoms and dipole potentials. The experiment was performed in a regime where the dynamics of the system were completely classical in nature. By adjust- ments of the shape of the billiard, it was demonstrated that the atomic motion within the billiard could be made stable and predictable or chaotic thereby al- lowing ergodic mixing. The subsequent experiment demonstrated the ability to control the center of mass motion of a collection of atoms without any a priori knowledge of the system. A minimally nondestructive method based on the quantum interaction of the atoms with a light field was used to measure the collective speed of the atoms. This information was utilized as a feedback signal to load the atoms into a co-moving trap that was subsequently brought to rest in the laboratory frame. Finally, Bose-Einstein condensation in one and two dimensions has been performed. This will allow for the experimental realization of the quantum tweezer for atoms. In this system, a Bose-Einstein condensate is used as a reservoir to extract single atoms. Taking advantage of the coherence properties of the condensate as well as the mean field inter- action of atoms within the tweezer, single atoms can be extracted with unit probability into the ground state of a dipole trap.Item Direct study of quantum statistics in a degenerate Bose gas(2006) Chuu, Chih-Sung; Raizen, Mark G.Item Exitonic condensation in bilayer systems(2008-08) Su, Jung-Jung; MacDonald, Allan H.Among the many examples of Bose condensation considered in physics, electron-hole-pair (exciton) condensation has maintained special interest because it has been difficult to realize experimentally, and because of controversy about condensate properties. In this thesis, we studied the various aspects of spontaneous symmetry broken state of exciton in bilayer using mean field theory. We calculated the photoluminescence of excitonic condensation created by laser. We developed a one-dimensional toy model of excitonic supercurrent using mean field theory plus non-equilibrium Green’s function (NEGF) which give qualitatively consistent results with experiments. We proposed graphene bilayer as a novel system for excitonic condensation to occur and estimate it to exist even at temperature as high as room temperature.Item Experiments with a Bose-Einstein condensate in a quasi-1D magnetic waveguide(2006) Henderson, Kevin Christopher; Raizen, Mark G.This thesis is primarily a comprehensive discussion of the development of two experimental studies: the quantum transport and effects of heating of ultracold atoms. It specifically provides details of the manipulation and control of ultracold atoms in magnetic waveguides, optical lattices, and optical billiards. The design, construction, and implementation of experimental apparati are also outlined and additional experimental tests are summarized, including the realization of a macroscopic transport (> 20 cm) system for ultracold atoms and transmission of ultracold atoms through a random optical potential. The first experiment is a study of the quantum transport for atoms confined in a periodic potential. These results include a comparison made of thermal and BEC initial conditions. Here, observation of ballistic transport is made for all values of well depth and initial conditions, and the expansion rates for thermal atoms are shown to be in excellent agreement with a singleparticle model. For weak wells (V0/ER ≤ 6), the expansion of the BEC is also in excellent agreement with single-particle theory, using an effective temperature model based on single (non-interacting) particle theory. For deep wells (V0/ER ≥ 6), a crossover is observed to a new regime for the BEC case, indicating the importance of interactions on quantum transport. The second experiment is a study of the effect of different heating rates on a dilute Bose gas confined in a quasi-1D finite, leaky box. An optical kicked-rotor is used to transfer energy to the atoms while two repulsive optical beams are used to confine the atoms. The average energy of the atoms is localized after a large number of kicks and the system reaches a nonequilibrium steady state. A numerical simulation of the experimental data suggests that the localization is due to energetic atoms leaking over the barrier. Our data also indicates a correlation between collisions and the destruction of the BoseEinstein condensate fraction and an exponential decay in phase space density.Item Experiments with Bose-Einstein condensation in an optical box(2005) Meyrath, Todd; Raizen, Mark G.Item Nonlinear dynamics of Bose-Einstein condensates(2005) Zhang, Chuanwei; Niu, Qian; Raizen, Mark G.Item Photoassociation experiments on ultracold and quantum gases in optical lattices(2004) Ryu, Changhyun; Heinzen, Daniel J.This thesis describes the results of several experiments that studied the photoassociation of an ultracold atomic Rb gas. In the first experiment, we produced ultracold diatomic molecules from an atomic gas via single-color photoassociation. The molecules were detected with resonance-enhanced multiphoton ionization. Trapping of these molecules in a quadrupole magnetic trap, with lifetimes up to 20 seconds, was also demonstrated. In addition, the rate constant for inelastic collisions between the trapped molecules and atoms was determined from measurements of the atomic density dependence of the decay rate of the trapped molecules. In another experiment, stimulated Raman photoassociation of Rb atoms in a Mott insulator state was studied. A Bose-Einstein condensate (BEC) of 87Rb atoms was loaded into a three-dimensional optical lattice formed by the interference pattern of three orthogonal standing wave laser fields. This system constitutes a very good realization of the Bose-Hubbard model, which predicts a quantum phase transition between a superfluid state and a Mott insulator state at a particular lattice height. A time-of-flight imaging method was used to study the state of the atomic gas, and the quantum phase transition was observed at the predicted lattice height. The signature of the phase transition was the disappearance and reappearance of peaks in the image that arose from the interference of atoms originating from different lattice sites. Two coherent laser fields were applied to the gas in its Mott insulating state, and tuned close to a Raman photoassociation resonance, and this resulted in an observable loss of atoms due to the formation of molecules. This transition exhibited a double-peaked spectrum, with one of the peaks arising from photoassociation of atoms in sites containing only two atoms, and the other from sites containing three atoms. Also, the loss of atoms vs. the duration of the Raman photoassociation period was studied, with the lasers tuned to the peak corresponding to two atoms per site. It was found that a central core of the gas, containing about 40 percent of the atoms, exhibited a coherent oscillation between an atomic and molecular quantum gas.Item Toward applications of shaped laser fields to ultracold boson systems(2015-05) Kohn, Rudolph Nicolas, Jr.; Heinzen, Daniel J.; Becker, Michael F; Downer, Michael C; Fiete, Gregory A; Sitz, Greg OExperimental progress toward the application of laser beams with shaped intensity profiles to dipole force trapping of ultracold atoms is reported. The experiment combines a new method for beam shaping, producing beams with intensity control to the 0.3% RMS level, with an apparatus designed to produce quantum degenerate gases of ⁸⁷Rb atoms. Experiments showing the production of ultracold ⁸⁷Rb and progress toward quantum degeneracy are discussed, along with several suggestions for the advancement to Bose condensation. Novel experiments with this apparatus are proposed, which would allow the investigation of specific points in phase space which have, until now, been difficult if not impossible to access. This work could lead to high-precision measurements of phase transitions, including quantum phase transitions and quantum criticality in a Bose or Bose-Hubbard gas.Item Two problems in many-body physics(2008-12) Wang, Cheng-Ching, 1975-; MacDonald, Allan H.In this dissertation, the applications of many-body physics in neutral bosons and electronic systems in transition metal oxides are discussed. In the first part of the thesis, I will introduce the concepts of Bose condensation, emphasize the significance of the order parameter in superfluids (macroscopic wave function), and its consequence such as the emergence of exotic vortex states under rotation. Dated back to the importance of the vortex dynamics in the properties of high T[subscript c] superconductors, people have introduced a dual vortex description to describe the dynamics of charged bosons in a magnetic field. Similarly, the dual description is adapted to the problems of neutral bosons under rotation. Based on that picture, vortices behave like charges in an effective magnetic field which has been known to demonstrate different quantum phases such as Wigner crystal phase, and fractional quantum Hall liquid phases depending on the relative fraction of the number of bosons and vortices. In this work, we would like to address the validity of the picture by low energy effective theory. We can identify the origin of the vortex masse and the parameter regimes in which the vortex dual description is appropriate. In the second part of the dissertation, density functional theory is used to describe the strongly correlated matters with local density approximation and local Hubbard U interaction(LDA+U). We are particularly interested in the interface states in the heterojunction systems of two different perovskite oxides. What we found is that the interface states can be engineered to appear in certain transitional metal oxide layers by controlling the number of positive and negative charged layers, leading to the formation of quantum wells in two dimension. This type of systems ignite the hope to search for broken symmetry states in the interface which can be tunable with chemical doping or electric field doping. Even room temperature superconducting state may or may not exist in the interface is still an intriguing issue.