Andreas Wagner
ContactDepartment of PhysicsUniversity of Basel Klingelbergstrasse 82 CH4056 Basel, Switzerland

Short Biography
I obtained my Diploma in Physics from the Freie Universitaet Berlin (Germany) in 2008. My diploma thesis is entitled "Avarage Density of States of AndreevGraphs" (field of research quantum chaology) and was supervised by Felix von Oppen and Sven Gnutzmann.Since November 2008, I'm a PhD student in the Condensed Matter Theory group at the University of Basel (Switzerland), under the supervision of Christoph Bruder.
Research Interests
» Ultracold atoms» Spinor Quantum Gases
» Quantum Information
Publications
Show all abstracts.1.  Meanfield analysis of spinor bosons in optical superlattices 
Andreas Wagner, Andreas Nunnenkamp, and Christoph Bruder. Phys. Rev. A 86, 023624 (2012)
We study the groundstate phase diagram of spinless and spin1 bosons in optical superlattices using a BoseHubbard Hamiltonian that includes spindependent interactions. We decouple the unit cells of the superlattice via a meanfield approach and take into account the dynamics within the unit cell exactly. 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 high
spin 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. Finally, we show that an energy offset between the two sites of the unit cell induces a staircase of singleatom tunneling resonances which surprisingly survives well into the superfluid regime.
 
2.  Spin1 Atoms in Optical Superlattices: SingleAtom Tunneling and Entanglement 
A. Wagner, C. Bruder, and E. Demler. Phys. Rev. A 84, 063636 (2011)
We examine spinor BoseEinstein condensates in optical superlattices theoretically using a BoseHubbard Hamiltonian that takes spin effects into account. Assuming that a small number of spin1 bosons is loaded in an optical 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. We use a doublewell potential as a unit cell for a onedimensional superlattice. Homogeneous and inhomogeneous magnetic fields are applied, and the effects of the linear and the quadratic Zeeman shifts are examined. 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 entanglements and show that the sum of these two terms gives a lower bound for the total entanglement.
