We study analytically the superfluid flow of a Bose-Einstein condensate in a ring geometry in presence of a rotating barrier. We show that a phase transition breaking a parity symmetry among two topological phases occurs at a critical value of the height of the barrier. Furthermore, a discontinuous (accompanied by hysteresis) phase transition is observed in the ordered phase when changing the angular velocity of the barrier. At the critical point where the hysteresis area vanishes, chemical potential of the ground state develops a cusp (a discontinuity in the first derivative). Along this path, the jump between the two corresponding states having a different winding number shows strict analogies with a topological phase transition. We finally study the current-phase relation of the system and compare some of our calculations with published experimental results.
Impurity-controlled vortex mobility and pair-breaking in fermionic superfluid rings
Institute of Physics, Polish Academy of Sciences（波兰科学院物理研究所）；Faculty of Physics, Warsaw University of Technology（华沙理工大学物理学院）；Department of Physics, University of Washington（华盛顿大学物理系）；Politecnico di Torino（都灵理工大学）
Breaking a superfluid harmonic dam: Observation and theory of Riemann invariants and accelerating sonic horizons
University of California, Merced（加州大学默塞德分校）；University of San Diego（圣地亚哥大学）；University of Colorado, Boulder（科罗拉多大学博尔德分校）；Washington State University（华盛顿州立大学）
Non local parity order in the two-dimensional Mott insulator
莫特绝缘体的特征在于在（整数）平均粒子密度n周围具有小的偏差，其中具有n-1和n+1个粒子的粒子对形成束缚态。在一维中，这种效应被非局部宇称“串”的非零值所捕获，而在密度波动较大的超流相中，这种非零值反而消失了。在这里，我们研究的相互作用诱导的过渡从超流的莫特绝缘体，在范式玻色哈伯德模型在n=1。通过量子蒙特卡罗模拟和LxM阶梯上的有限尺寸标度分析，我们探讨了L从一维走向无穷大时“膜”宇称算符的行为（即，M=1）到二维（即，M走向无穷大）。我们证实了这样的猜想，即采用标准定义，它们的平均值在二维中也在绝缘相中衰减到零，评估了“周长定律”的比例因子[S. P. Rath等人，Ann. Phys.（N.Y.）334，256（2013）]。在膜宇称中引入另一个相位后，我们证明了它的期望值在绝缘体中变得非零，而在向超流相的过渡中仍然消失。这些量可直接用于实验测量，从而提供了莫特绝缘体的深刻特征。
