Andreas Wagner


Department of Physics
University of Basel
Klingelbergstrasse 82
CH-4056 Basel, Switzerland

email:view address

tel: +41 61 267 36 53
fax:+41 61 267 13 49

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 Andreev-Graphs" (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


Show all abstracts.

1.  Mean-field analysis of spinor bosons in optical superlattices
Andreas Wagner, Andreas Nunnenkamp, and Christoph Bruder.
Phys. Rev. A 86, 023624 (2012)

We study the ground-state phase diagram of spinless and spin-1 bosons in optical superlattices using a Bose-Hubbard Hamiltonian that includes spin-dependent interactions. We decouple the unit cells of the superlattice via a mean-field approach and take into account the dynamics within the unit cell exactly. The system supports Mott-insulating as well as superfluid phases. The transitions between these phases are second-order for spinless bosons and second- or first-order for spin-1 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 first-order phase transitions. Finally, we show that an energy offset between the two sites of the unit cell induces a staircase of single-atom tunneling resonances which surprisingly survives well into the superfluid regime.

2.  Spin-1 Atoms in Optical Superlattices: Single-Atom Tunneling and Entanglement
A. Wagner, C. Bruder, and E. Demler.
Phys. Rev. A 84, 063636 (2011)

We examine spinor Bose-Einstein condensates in optical superlattices theoretically using a Bose-Hubbard Hamiltonian that takes spin effects into account. Assuming that a small number of spin-1 bosons is loaded in an optical potential, we study single-particle tunneling that occurs when one lattice site is ramped up relative to a neighboring site. Spin-dependent 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 spin-1 bosons in an optical superlattice a model for mesoscopic magnetism. We use a double-well potential as a unit cell for a one-dimensional 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.