Trotzky S, Cheinet P, Fölling S, Feld M, Schnorrberger U, Rey A M, Polkovnikov A, Demler E A, Lukin M D, Bloch I
Institut für Physik, Johannes Gutenberg-Universität, 55099 Mainz, Germany.
Science. 2008 Jan 18;319(5861):295-9. doi: 10.1126/science.1150841. Epub 2007 Dec 20.
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.
量子力学超交换相互作用构成了强关联电子介质中量子磁性的基础。我们报道了利用光学晶格中的超冷原子对超交换相互作用进行的直接测量。在将超冷原子的自旋混合物制备成反铁磁有序状态后，我们测量了耦合能量从5赫兹到1千赫兹的相干超交换介导的自旋动力学。通过动态改变相邻晶格位点之间的势垒，超交换相互作用的大小和符号可以得到控制，从而使系统能够在反铁磁和铁磁自旋相互作用之间切换。我们将我们的发现与两格点玻色-哈伯德模型的预测进行了比较，发现吻合度非常高，但我们也能够识别出可以通过纳入直接最近邻相互作用来解释的修正。
