Strong dipolar effects in a quantum ferrofluid
Strong dipolar effects in a quantum ferrofluid
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DOI：
10.1038/nature06036
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发表时间：
2007-08-09
期刊：
影响因子：
64.8
通讯作者：
Pfau, Tilman
中科院分区：
文献类型：
--
作者：
Lahaye, Thierry;Koch, Tobias;Pfau, Tilman
对称性破缺相互作用在许多物理学领域都有着重要的作用，从经典的铁磁流体到超流He-3和d波超导。对于超流量子气体，人们期待着由电偶极子或磁偶极子之间的破缺相互作用产生的各种新的物理现象（1）。对偶极玻色子预言了光学晶格中的新量子相，如棋盘相或超固相（2，3）。偶极相互作用也可以大大丰富具有内部自由度的量子气体的物理学（4-6）。偶极粒子阵列可以用于有效的量子信息处理（7）。在这里，我们报告的实现铬玻色爱因斯坦凝聚与强偶极相互作用。通过使用Feshbach共振，我们减少了通常的各向同性接触相互作用，使Cr-52原子之间的各向异性磁偶极-偶极相互作用的强度变得相当。这导致了原子云的长宽比的变化;对于强偶极相互作用，膨胀过程中椭圆率的反转（玻色-爱因斯坦凝聚的通常“确凿证据”）可以被抑制。这些影响占考虑到偶极相互作用的超流体流体动力学方程中的气体的动力学，以同样的方式，经典的铁磁流体可以被描述为包括偶极项在经典的流体动力学方程。我们的研究结果是探索量子铁磁流体独特性质的第一步。
Symmetry-breaking interactions have a crucial role in many areas of physics, ranging from classical ferrofluids to superfluid He-3 and d-wave superconductivity. For superfluid quantum gases, a variety of new physical phenomena arising from the symmetry-breaking interaction between electric or magnetic dipoles are expected(1). Novel quantum phases in optical lattices, such as chequerboard or supersolid phases, are predicted for dipolar bosons(2,3). Dipolar interactions can also enrich considerably the physics of quantum gases with internal degrees of freedom(4-6). Arrays of dipolar particles could be used for efficient quantum information processing(7). Here we report the realization of a chromium Bose-Einstein condensate with strong dipolar interactions. By using a Feshbach resonance, we reduce the usual isotropic contact interaction, such that the anisotropic magnetic dipole-dipole interaction between Cr-52 atoms becomes comparable in strength. This induces a change of the aspect ratio of the atom cloud; for strong dipolar interactions, the inversion of ellipticity during expansion (the usual 'smoking gun' evidence for a Bose-Einstein condensate) can be suppressed. These effects are accounted for by taking into account the dipolar interaction in the superfluid hydrodynamic equations governing the dynamics of the gas, in the same way as classical ferrofluids can be described by including dipolar terms in the classical hydrodynamic equations. Our results are a first step in the exploration of the unique properties of quantum ferrofluids.