Ground state of an ultracold Fermi gas of tilted dipoles in elongated traps
Ground state of an ultracold Fermi gas of tilted dipoles in elongated traps
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DOI：
10.1088/1367-2630/aade24
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发表时间：
2018-06
影响因子：
3.3
通讯作者：
Vladimir Veljić;Aristeu R P Lima;L. Chomaz;S. Baier;M. Mark;F. Ferlaino;A. Pelster;A. Balaž
中科院分区：
文献类型：
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作者：
Vladimir Veljić;Aristeu R P Lima;L. Chomaz;S. Baier;M. Mark;F. Ferlaino;A. Pelster;A. Balaž
费米气体中的多体偶极效应是相当微妙的，因为它们与费米表面（FS）处和下方的大动能竞争。最近，在铒原子样品中实验观察到，由于各向异性和长程偶极-偶极相互作用的存在，其FS从球体变形为椭球体Aikawa等人（2014 Science 345 1484）。此外，有人建议，当偶极旋转的外部场的手段，FS遵循他们的旋转，从而保持长轴的动量空间椭球平行的偶极。在这里，我们概括了以前的Hartree-Fock平均场理论的系统限制在一个细长的三轴陷阱与任意取向的偶极子相对于陷阱。由此我们首次研究了偶极子的任意取向对系统基态性质的影响。此外，考虑到系统的几何形状，我们展示了如何椭球FS变形可以重建，假设弹道膨胀，从实验测量的真实空间的纵横比自由膨胀后。我们比较我们的理论结果与新的实验数据测量的铒费米气体的各种陷阱参数和偶极子取向。所观察到的显着的一致性表明，我们的模型捕捉FS变形的完整的角度依赖性的能力。此外，对于具有更高偶极矩的系统，我们的理论预测了一个额外的意想不到的效果：FS不简单地严格遵循偶极子的取向，但软化显示纵横比的变化取决于偶极子的取向相对于陷阱的几何形状，以及陷阱的各向异性本身。我们的理论提供了理解和解释现象的基础，在这些现象中，所研究的物理学取决于FS的基本结构，如费米子配对和超流性。
Many-body dipolar effects in Fermi gases are quite subtle as they energetically compete with the large kinetic energy at and below the Fermi surface (FS). Recently it was experimentally observed in a sample of erbium atoms that its FS is deformed from a sphere to an ellipsoid due to the presence of the anisotropic and long-range dipole–dipole interaction Aikawa et al (2014 Science 345 1484). Moreover, it was suggested that, when the dipoles are rotated by means of an external field, the FS follows their rotation, thereby keeping the major axis of the momentum-space ellipsoid parallel to the dipoles. Here we generalise a previous Hartree–Fock mean-field theory to systems confined in an elongated triaxial trap with an arbitrary orientation of the dipoles relative to the trap. With this we study for the first time the effects of the dipoles’ arbitrary orientation on the ground-state properties of the system. Furthermore, taking into account the geometry of the system, we show how the ellipsoidal FS deformation can be reconstructed, assuming ballistic expansion, from the experimentally measurable real-space aspect ratio after a free expansion. We compare our theoretical results with new experimental data measured with erbium Fermi gas for various trap parameters and dipole orientations. The observed remarkable agreement demonstrates the ability of our model to capture the full angular dependence of the FS deformation. Moreover, for systems with even higher dipole moment, our theory predicts an additional unexpected effect: the FS does not simply follow rigidly the orientation of the dipoles, but softens showing a change in the aspect ratio depending on the dipoles’ orientation relative to the trap geometry, as well as on the trap anisotropy itself. Our theory provides the basis for understanding and interpreting phenomena in which the investigated physics depends on the underlying structure of the FS, such as fermionic pairing and superfluidity.