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Effects of interaction in Bose-Einstein condensates

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dc.contributor.advisor Wolfgang Ketterle. en_US Xu, Kaiwen en_US
dc.contributor.other Massachusetts Institute of Technology. Dept. of Physics. en_US 2007-04-20T15:51:35Z 2007-04-20T15:51:35Z 2006 en_US 2006 en_US
dc.description Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2006. en_US
dc.description Includes bibliographical references (p. 150-167). en_US
dc.description.abstract This thesis discusses a series of studies that investigate the effects of interaction - essentially the s-wave scattering - in the various properties of Bose-Einstein condensates (BEC). The phonon wavefunction in a BEC was measured using Bragg spectroscopy and compared with the well-known Bogoliubov theory. Phonons were first excited in a BEC of 3 x 107 condensed 23Na atoms via small-angle two-photon Bragg scattering. Large angle Bragg scattering was then used to probe the momentum distribution. We found reasonable agreement with the theory. With the same technique of Bragg diffraction, we studied the four-wave mixing process for matter waves. The BEC was split into two strong source waves and a weak seed wave. The s-wave scattering coherently mixed pairs of atoms from the sources into the seed and its conjugate wave, creating a pair-correlated atomic beams with "squeezed" number difference. A Feshbach resonance was used to produce ultracold Na2 molecules with initial phase-space density in excess of 20. Starting from an atomic BEC, a magnetic field ramp shifted a bound state from above the threshold of the unbound continuum to below, creating a molecular population with almost zero center-of-mass motion. en_US
dc.description.abstract (cont.) A reverse field ramp dissociated the cold molecules into free atom pairs carrying kinetic energy dependent on the ramp speed. This dependence provided a measure of the coupling strength between the bound state and the continuum. Condensates were loaded into optical lattices formed with retro-reflected single frequency lasers. Quantum phase transition from the superfluid state to Mott-insulator state was observed in a three dimensional lattice. The increased interaction and flattened dispersion relation led to strongly enhanced quantum depletion in the superfluid state. en_US
dc.description.statementofresponsibility by Kaiwen Xu. en_US
dc.format.extent 167 p. en_US
dc.language.iso eng en_US
dc.publisher Massachusetts Institute of Technology en_US
dc.rights M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission. en_US
dc.subject Physics. en_US
dc.title Effects of interaction in Bose-Einstein condensates en_US
dc.title.alternative Effects of interaction in BEC en_US
dc.type Thesis en_US Ph.D. en_US
dc.contributor.department Massachusetts Institute of Technology. Dept. of Physics. en_US
dc.identifier.oclc 82144119 en_US

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