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Transition from a Two-Dimensional Superfluid to a One-Dimensional Mott Insulator
Department of Theoretical Physics, Royal Institute of Technology, AlbaNova, SE-106 91 Stockholm, Sweden.
Department of Theoretical Physics, Royal Institute of Technology, AlbaNova, SE-106 91 Stockholm, Sweden.
Umeå University, Faculty of Science and Technology, Physics.
Umeå University, Faculty of Science and Technology, Physics.
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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.

Place, publisher, year, edition, pages
2007. Vol. 99, no 11, 110401- p.
Identifiers
URN: urn:nbn:se:umu:diva-18169DOI: 10.1103/PhysRevLett.99.110401OAI: oai:DiVA.org:umu-18169DiVA: diva2:157842
Available from: 2007-11-28 Created: 2007-11-28 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Experimental and Numerical Investigations of Ultra-Cold Atoms
Open this publication in new window or tab >>Experimental and Numerical Investigations of Ultra-Cold Atoms
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

I have been one of the main responsible for building a new laboratory for Bose-Einstein condensation with 87Rb. In particular, the experimental setup has been designed for performing experiments with Bose-Einstein condensates load into optical lattices of variable geometries.

All parts essential for Bose-Einstein condensation are in place. Atoms are collected in a magneto-optical trap, transferred to another vacuum chamber, with better vacuum, and trapped in another magneto-optical trap. Atoms are successfully transferred to a dark magnetic trap, and system for diagnostics with absorption imaging has been realized. We have not yet been able to form a Bose-Einstein condensate, due to a range of technical difficulties.

Equipment for alignment of optical lattices with flexible geometry has been designed, built, and tested. This tool has been proven to work as desired, and there is a great potential for a range of unique experiments with Bose-Einstein condensates in optical lattices of various geometries, including superlattices and quasi-periodic lattices.

Numerical studies have been made on anisotropic optical lattices, and the existence of a transition between a 2D superfluid phase and a 1D Mott-insulating phase has been confirmed. We have shown that the transition is of Berezinskii-Kosterlitz-Thouless type. In another numerical study it has been shown that using stimulated Raman transitions is a practical method for transferring atoms between states in a double optical lattice. Thus, it will be possible to transfer populations between the lattices, with further applications in qubit read/write operations.

Place, publisher, year, edition, pages
Umeå: Fysik, 2007. 50 p.
Keyword
Ultracold atoms, optical lattices, Bose-Einstein condensation, quantum phase transitions
National Category
Physical Sciences
Identifiers
urn:nbn:se:umu:diva-1453 (URN)978-91-7264-466-3 (ISBN)
Public defence
2007-12-17, N450, Naturvetarhuset, 13:00 (English)
Opponent
Supervisors
Available from: 2007-11-26 Created: 2007-11-26 Last updated: 2009-06-30Bibliographically approved
2. Ultracold rubidium atoms in periodic potentials
Open this publication in new window or tab >>Ultracold rubidium atoms in periodic potentials
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
Bose-Einstein condensation, optical lattice, quantum phase transition, experiment, theory
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:umu:diva-1821 (URN)978-91-7264-628-5 (ISBN)
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

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