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Ultracold rubidium atoms in periodic potentials
Umeå University, Faculty of Science and Technology, Physics.
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis includes both experimental and theoretical investigations, presented in a series of eight papers. The experimental part ranges from the construction procedures of an apparatus for Bose-Einstein condensates, to full scale experiments using three different set-ups for ultracold atoms in optical lattices. As one of the main themes of the thesis, an experimental apparatus for production of Bose-Einstein Condensates is under construction. A magneto-optically trapped sample, hosting more than 200 million 87Rb atoms, have successfully been loaded into a magnetic trap with high transfer rate. The lifetime of the sample in the magnetic trap is in the range of 9 s, and the atoms have been shown to respond to evaporative cooling. The experiment is ready for optimization of the magnetic trap loading, and evaporative cooling parameters, which are the final steps for reaching Bose-Einstein condensation. The set-up is designed to host experiments including variable geometry optical lattices, and includes the possibility to align laser beams with high angular precision for this purpose. The breakdown of Bloch waves in a Bose-Einstein condensate is studied, attributed to the effect of energetic and dynamical instability. This experimental study is performed using a Bose-Einstein condensate in a moving one-dimensional optical lattice at LENS, Florence Italy. The optical lattice parameters, and the thermal distribution of the atomic sample required to trigger the instabilities, are detected, and compared with a theoretical model developed in parallel with the experiments. In close connection with these one-dimensional lattice studies, an experimental survey to characterize regimes of superradiant Rayleigh scattering and Bragg scattering is presented. Tunneling properties of repulsively bound atom pairs in double well potentials are characterized in an experiment at Johannes Gutenberg University, Mainz Germany. A three-dimensional optical lattice, producing an array of double wells with tunable properties is let to interact with a Bose-Einstein condensate. Pairs of ultracold atoms are produced on one side in the double wells, and their tunneling behavior, dependent on potential barrier and repulsion properties, is studied. A theoretical study of the crossover between one- and two-dimensional systems has been performed. The simulations were made for a two-dimensional array of atoms, where the behavior for different tunneling probabilities and atom-atom repulsion strengths was studied. Scaling relations for systems of variable sizes have been examined in detail, and numerical values for the involved variables have been found.

Place, publisher, year, edition, pages
Umeå: Fysik , 2008. , 105 p.
Keyword [en]
Bose-Einstein condensation, optical lattice, quantum phase transition, experiment, theory
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:umu:diva-1821ISBN: 978-91-7264-628-5 (print)OAI: oai:DiVA.org:umu-1821DiVA: diva2:142124
Public defence
2008-10-03, N200, Naturvetarhuset, Umeå Universitet, Umeå, 10:15 (English)
Opponent
Supervisors
Available from: 2008-09-12 Created: 2008-09-11 Last updated: 2009-06-30Bibliographically approved
List of papers
1. Observation of Dynamical Instability for a Bose-Einstein Condensate in a Moving 1D Optical Lattice
Open this publication in new window or tab >>Observation of Dynamical Instability for a Bose-Einstein Condensate in a Moving 1D Optical Lattice
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2004 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 93, no 14, 140406- p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-3430 (URN)10.1103/PhysRevLett.93.140406 (DOI)
Available from: 2008-09-12 Created: 2008-09-12 Last updated: 2017-12-14Bibliographically approved
2. Unstable regimes for a Bose-Einstein condensate in an optical lattice
Open this publication in new window or tab >>Unstable regimes for a Bose-Einstein condensate in an optical lattice
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2005 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 72, 013603- p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-3431 (URN)10.1103/PhysRevA.72.013603 (DOI)
Available from: 2008-09-12 Created: 2008-09-12 Last updated: 2017-12-14Bibliographically approved
3. Dynamics of Bloch Matter Waves and Its Breakdown: a Bose-Einstein Condensate in a Moving 1D Optical Lattice
Open this publication in new window or tab >>Dynamics of Bloch Matter Waves and Its Breakdown: a Bose-Einstein Condensate in a Moving 1D Optical Lattice
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2005 (English)In: CMES - Computer Modeling in Engineering & Sciences, ISSN 1526-1492, E-ISSN 1526-1506, Vol. 7, no 3, 447-453 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-3432 (URN)
Available from: 2008-09-12 Created: 2008-09-12 Last updated: 2017-12-14Bibliographically approved
4. From superradiant Rayleigh scattering to Bragg scattering
Open this publication in new window or tab >>From superradiant Rayleigh scattering to Bragg scattering
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2005 (English)In: European Physical Journal D: Atomic, Molecular and Optical Physics, ISSN 1434-6060, E-ISSN 1434-6079, Vol. 32, no 2, 167-170 p.Article in journal (Refereed) Published
Abstract [en]

We present the results of an experiment on light scattering from an elongated Bose-Einstein condensate interacting with far off resonant laser light. Due to superradiant Rayleigh scattering a coherent superposition of two atomic wavepackets with different momenta forms in the presence of a single laser beam. Varying the intensity of a weak counterpropagating laser beam we observe the transition from the pure superradiant regime to the Bragg scattering regime, where Rabi oscillations in a two-level system are observed. The process is limited by the decoherence between the two atomic wavepackets.

Identifiers
urn:nbn:se:umu:diva-3433 (URN)10.1140/epjd/e2004-00124-1 (DOI)
Available from: 2008-09-12 Created: 2008-09-12 Last updated: 2017-12-14Bibliographically approved
5. A set-up for flexible geometry optical lattices
Open this publication in new window or tab >>A set-up for flexible geometry optical lattices
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2008 (English)In: European Physical Journal: Applied physics, ISSN 1286-0042, E-ISSN 1286-0050, Vol. 42, 269-273 p.Article in journal (Refereed) Published
Abstract [en]

We have developed an alignment tool for optical lattices with arbitrary beam angles, allowing for optical potentials with a range of geometries and topographies. A calibration procedure has been introduced, giving a precision of 10 mrad in the chosen beam angle, and a high degree of flexibility. The tool has been tested in simplified experiments on the confinement and expansion of cold atoms in one-dimensional and two-dimensional optical lattices, and has proved to work well.

Identifiers
urn:nbn:se:umu:diva-10492 (URN)doi:10.1051/epjap:2008086 (DOI)
Available from: 2008-09-17 Created: 2008-09-17 Last updated: 2017-12-14Bibliographically approved
6. Direct observation of second-order atom tunnelling
Open this publication in new window or tab >>Direct observation of second-order atom tunnelling
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2007 (English)In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 448, no 7157, 1029-1032 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-3435 (URN)10.1038/nature06112 (DOI)
Available from: 2008-09-12 Created: 2008-09-12 Last updated: 2017-12-14Bibliographically approved
7. Transition from a Two-Dimensional Superfluid to a One-Dimensional Mott Insulator
Open this publication in new window or tab >>Transition from a Two-Dimensional Superfluid to a One-Dimensional Mott Insulator
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2007 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 99, no 11, 110401- p.Article in journal (Refereed) Published
Abstract [en]

A two-dimensional system of atoms in an anisotropic optical lattice is studied theoretically. If the system is finite in one direction, it is shown to exhibit a transition between a two-dimensional superfluid and a one-dimensional Mott insulating chain of superfluid tubes. Monte Carlo simulations are consistent with the expectation that the phase transition is of Kosterlitz-Thouless type. The effect of the transition on experimental time-of-flight images is discussed.

Identifiers
urn:nbn:se:umu:diva-18169 (URN)10.1103/PhysRevLett.99.110401 (DOI)
Available from: 2007-11-28 Created: 2007-11-28 Last updated: 2017-12-14Bibliographically approved
8. One-dimensional phase transitions in a two-dimensional optical lattice
Open this publication in new window or tab >>One-dimensional phase transitions in a two-dimensional optical lattice
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2008 (English)In: European Physical Journal D: Atomic, Molecular and Optical Physics, ISSN 1434-6060, E-ISSN 1434-6079, Vol. 49, no 2, 223-230 p.Article in journal (Refereed) Published
Abstract [en]

A phase transition for bosonic atoms in a two-dimensional anisotropic optical lattice is considered. If the tunnelling rates in two directions are different, the system can undergo a transition between a two-dimensional superfluid and a one-dimensional Mott insulating array of strongly coupled tubes. The connection to other lattice models is exploited in order to better understand the phase transition. Critical properties are obtained using quantum Monte Carlo calculations. These critical properties are related to correlation properties of the bosons and a criterion for commensurate filling is established.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:umu:diva-10486 (URN)10.1140/epjd/e2008-00152-9 (DOI)
Available from: 2008-09-16 Created: 2008-09-16 Last updated: 2017-12-14Bibliographically approved

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