Wagner, Andreas. Spinor condensates in optical superlattices. 2012, PhD Thesis, University of Basel, Faculty of Science.

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Official URL: http://edoc.unibas.ch/diss/DissB_10215
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Abstract
In this thesis we study various aspects of spinor BoseEinstein condensates in optical superlattices using a BoseHubbard Hamiltonian that takes spin effects into account. We decouple the unit cells of the superlattice via a meanfield approach and take into account the dynamics within the unit cell exactly. In this way we derive the groundstate phase diagram of spinor bosons in superlattices. The system supports Mottinsulating as well as superfluid phases. The transitions between these phases are secondorder for spinless bosons and second or firstorder for spin1 bosons. Antiferromagnetic interactions energetically penalize highspin configurations and elongate all Mott lobes, especially the ones corresponding to an even atom number on each lattice site. We find that the quadratic Zeeman effect lifts the degeneracy between different polar superfluid phases leading to additional metastable phases and firstorder phase transitions. A change of magnetic fields can drive quantum phase transitions in the same way as a change in the tunneling amplitude does. Furthermore we study the physics of spin1 atoms in superlattices deep in the Mott insulating phase when the superlattice decomposes into isolated doublewell potentials. Assuming that a small number of spin1 bosons is loaded in an optical doublewell potential, we study singleparticle tunneling that occurs when one lattice site is ramped up relative to a neighboring site. Spindependent effects modify the tunneling events in a qualitative and quantitative way. Depending on the asymmetry of the double well different types of magnetic order occur, making the system of spin1 bosons in an optical superlattice a model for mesoscopic magnetism with an unprecedented control of the parameters. Homogeneous and inhomogeneous magnetic fields are applied and the effects of the linear and the quadratic Zeeman shifts are examined. We generalize the concept of bosonic staircases to connected doublewell potentials. We show that an energy offset between the two sites of the unit cell in an extended superlattice induces a staircase of singleatom resonances in
the same way as in isolated double well. We also examine singleatom resonances in the superfluid regime and find clear fingerprints of them in the superfluid density. We also investigate the bipartite entanglement between the sites and construct states of maximal entanglement. The entanglement in our system is due to both orbital and spin degrees of freedom. We calculate the contribution of orbital and
spin entanglement and show that the sum of these two terms gives a lower bound for the total entanglement.
the same way as in isolated double well. We also examine singleatom resonances in the superfluid regime and find clear fingerprints of them in the superfluid density. We also investigate the bipartite entanglement between the sites and construct states of maximal entanglement. The entanglement in our system is due to both orbital and spin degrees of freedom. We calculate the contribution of orbital and
spin entanglement and show that the sum of these two terms gives a lower bound for the total entanglement.
Advisors:  Bruder, Christoph 

Committee Members:  Jaksch, Dieter 
Faculties and Departments:  05 Faculty of Science > Departement Physik > Physik > Theoretische Physik (Bruder) 
UniBasel Contributors:  Wagner, Andreas and Bruder, Christoph 
Item Type:  Thesis 
Thesis no:  10215 
Thesis status:  Complete 
Bibsysno:  Link to catalogue 
Number of Pages:  164 S. 
Language:  English 
Identification Number: 

Last Modified:  22 Jan 2018 15:51 
Deposited On:  14 Jan 2013 15:48 
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