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Originally published in Science Express on 20 December 2007
Science 18 January 2008:
Vol. 319. no. 5861, pp. 295 - 299
DOI: 10.1126/science.1150841
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Research Articles

Time-Resolved Observation and Control of Superexchange Interactions with Ultracold Atoms in Optical Lattices

S. Trotzky,1* P. Cheinet,1* S. Fölling,1 M. Feld,1,2 U. Schnorrberger,1 A. M. Rey,3 A. Polkovnikov,4 E. A. Demler,3,5 M. D. Lukin,3,5 I. Bloch1{dagger}

Quantum mechanical superexchange interactions form the basis of quantum magnetism in strongly correlated electronic media. We report on the direct measurement of superexchange interactions with ultracold atoms in optical lattices. After preparing a spin-mixture of ultracold atoms in an antiferromagnetically ordered state, we measured coherent superexchange-mediated spin dynamics with coupling energies from 5 hertz up to 1 kilohertz. By dynamically modifying the potential bias between neighboring lattice sites, the magnitude and sign of the superexchange interaction can be controlled, thus allowing the system to be switched between antiferromagnetic and ferromagnetic spin interactions. We compare our findings to predictions of a two-site Bose-Hubbard model and find very good agreement, but are also able to identify corrections that can be explained by the inclusion of direct nearest-neighbor interactions.

1 Institut für Physik, Johannes Gutenberg-Universität, 55099 Mainz, Germany.
2 Fachbereich Physik, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany.
3 Institute for Theoretical Atomic, Molecular and Optical Physics, Harvard-Smithsonian Center of Astrophysics, Cambridge, MA 02138, USA.
4 Department of Physics, Boston University, Boston, MA 02215, USA.
5 Physics Department, Harvard University, Cambridge, MA 02138, USA.

* These authors contributed equally to this work.

{dagger} To whom correspondence should be addressed. E-mail: bloch{at}uni-mainz.de

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Itinerant Ferromagnetism with Ultracold Atoms.
W. Zwerger (2009)
Science 325, 1507-1509
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Quantum Gases.
I. Bloch (2008)
Science 319, 1202-1203
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