人工晶体中超流体密度的各向异性观测
Observation of anisotropic superfluid density in an artificial crystal
AI总结：
本研究通过实验和理论探究一维光学晶格中原子超流体玻色-爱因斯坦凝聚体的各向异性声速，发现光学晶格导致超流体密度降低并伴随正常流体出现，同时利用剪刀模式实验证明旋转流存在，揭示了超固态性质。
摘要：
我们通过实验和理论研究了位于一维光学晶格中的原子超流体（SF）玻色-爱因斯坦凝聚体中各向异性的声速。由于声速源于SF密度，这意味着SF密度本身也是各向异性的。我们发现声速因光学晶格而降低，SF密度也随之降低。这种降低伴随着在纯玻色凝聚相中正常流体的出现。SF密度的降低——最初由A. J. Leggett在超固态背景下预测[Phys. Rev. Lett. 1543--1546 (1970)]——源于超流性与密度调制的共存，但与调制的起源无关。我们还在剪刀模式实验中测量了系统的转动惯量，证明了旋转流的存在。因此，我们利用外加的而非自发形成的密度有序性，阐明了一些超固态性质。
英文摘要：
We experimentally and theoretically investigate the anisotropic speed of sound of an atomic superfluid (SF) Bose-Einstein condensate in a 1D optical lattice. Because the speed of sound derives from the SF density, this implies that the SF density is itself anisotropic. We find that the speed of sound is decreased by the optical lattice, and the SF density is concomitantly reduced. This reduction is accompanied by the appearance of a normal fluid in the purely Bose condensed phase. The reduction in SF density -- first predicted [A. J. Leggett, Phys. Rev. Lett. 1543--1546 (1970)] in the context of supersolidity -- results from the coexistence of superfluidity and density modulations, but is agnostic about the origin of the modulations. We additionally measure the moment of inertia of the system in a scissors mode experiment, demonstrating the existence of rotational flow. As such we shed light on some supersolid properties using imposed, rather than spontaneously formed, density-order.
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