Gemelke Nathan, Zhang Xibo, Hung Chen-Lung, Chin Cheng
The James Franck Institute and Department of Physics, University of Chicago, Chicago, Illinois 60637, USA.
Nature. 2009 Aug 20;460(7258):995-8. doi: 10.1038/nature08244.
The observation of the superfluid to Mott insulator phase transition of ultracold atoms in optical lattices was an enabling discovery in experimental many-body physics, providing the first tangible example of a quantum phase transition (one that occurs even at zero temperature) in an ultracold atomic gas. For a trapped gas, the spatially varying local chemical potential gives rise to multiple quantum phases within a single sample, complicating the interpretation of bulk measurements. Here we report spatially resolved, in-situ imaging of a two-dimensional ultracold atomic gas as it crosses the superfluid to Mott insulator transition, providing direct access to individual characteristics of the insulating, superfluid and normal phases. We present results for the local compressibility in all phases, observing a strong suppression in the insulator domain and suppressed density fluctuations for the Mott insulator, in accordance with the fluctuation-dissipation theorem. Furthermore, we obtain a direct measure of the finite temperature of the system. Taken together, these methods enable a complete characterization of multiple phases in a strongly correlated Bose gas, and of the interplay between quantum and thermal fluctuations in the quantum critical regime.
对光学晶格中超冷原子从超流体到莫特绝缘体相变的观测是实验多体物理学中的一项开创性发现，它为超冷原子气体中的量子相变（即使在零温度下也会发生的相变）提供了首个切实的例子。对于捕获的气体，空间变化的局部化学势会在单个样本中产生多个量子相，这使得对整体测量结果的解释变得复杂。在此，我们报告了二维超冷原子气体在跨越超流体到莫特绝缘体相变时的空间分辨原位成像，从而能够直接获取绝缘相、超流体相和正常相的个体特征。我们给出了所有相中局部压缩性的结果，观察到在绝缘体区域有强烈的抑制，并且根据涨落耗散定理，莫特绝缘体的密度涨落受到抑制。此外，我们获得了系统有限温度的直接测量值。综合起来，这些方法能够对强关联玻色气体中的多个相以及量子临界区域中量子涨落和热涨落之间的相互作用进行完整的表征。
