Sharp peaks in the momentum distribution of bosons in optical lattices in the normal state
Sharp peaks in the momentum distribution of bosons in optical lattices in the normal state
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DOI：
10.1038/nphys983
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发表时间：
2008-08
期刊：
影响因子：
19.6
通讯作者：
Y. Kato;Qi Zhou;N. Kawashima;N. Trivedi
中科院分区：
文献类型：
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作者：
Y. Kato;Qi Zhou;N. Kawashima;N. Trivedi
光学晶格中的冷原子为研究强关联超流相和Mott绝缘体相之间的量子相变提供了一个独特的实验室。实验分析的主要瓶颈之一是一套明确的标准来识别超流相。在飞行时间实验中，一种“尖锐”的干涉图样被广泛地用作超流性的标志。在这里，我们表明，尖峰是不是一个可靠的诊断超流性。利用大规模量子Monte Carlo方法模拟了N =1.4× 104粒子的三维玻色-哈伯德模型，计算了动量分布n（k）与温度T和T/U（跳跃与就地排斥的比值）的关系.我们发现，即使在转变温度Tc以上的超流密度和冷凝分数消失，干涉图案仍然可以有尖锐的峰值骑在一个广泛的背景。我们确定了超流体的真实特征，并对为什么在正常状态下会出现如此尖锐的峰有了更深入的理解。
Cold atoms in optical lattices provide a unique laboratory for investigating quantum phase transitions between strongly correlated superfluid and Mott insulator phases,. One of the major bottlenecks in the analysis of experiments is a clear set of criteria for identifying the superfluid phase. A ‘sharp’ interference pattern in time-of-flight experiments has been widely adopted as a signature of superfluidity,,,,. Here, we show that sharp peaks are not a reliable diagnostic of superfluidity. Using large-scale quantum Monte Carlo simulations of the Bose–Hubbard model in three dimensions with up toN=1.4×104particles, we calculate the momentum distributionn(k) as a function of temperatureTandt/U, the ratio of hopping to the onsite repulsion. We find that even above the transition temperatureTcwhere both superfluid density and condensate fraction vanish, the interference pattern can nevertheless have sharp peaks riding over a broad background. We identify the true signature of the superfluid and give a deeper understanding of why such sharp peaks appear in the normal state.