Hurst Hilary M, Efimkin Dmitry K, Spielman I B, Galitski Victor
Joint Quantum Institute and Condensed Matter Theory Center, Department of Physics, University of Maryland, College Park, Maryland 20742-4111, USA.
The Center for Complex Quantum Systems, The University of Texas at Austin, Austin, Texas 78712-1192, USA.
Phys Rev A (Coll Park). 2017 May;95(5). doi: 10.1103/PhysRevA.95.053604. Epub 2017 May 3.
We study controllable friction in a system consisting of a dark soliton in a one-dimensional Bose-Einstein condensate coupled to a noninteracting Fermi gas. The fermions act as impurity atoms, not part of the original condensate, that scatter off of the soliton. We study semiclassical dynamics of the dark soliton, a particlelike object with negative mass, and calculate its friction coefficient. Surprisingly, it depends periodically on the ratio of interspecies (impurity-condensate) to intraspecies (condensate-condensate) interaction strengths. By tuning this ratio, one can access a regime where the friction coefficient vanishes. We develop a general theory of stochastic dynamics for negative-mass objects and find that their dynamics are drastically different from their positive-mass counterparts: they do not undergo Brownian motion. From the exact phase-space probability distribution function (i.e., in position and velocity), we find that both the trajectory and lifetime of the soliton are altered by friction, and the soliton can undergo Brownian motion only in the presence of friction and a confining potential. These results agree qualitatively with experimental observations by Aycock [Proc. Natl. Acad. Sci. USA , 2503 (2017)] in a similar system with bosonic impurity scatterers.
我们研究了一个由一维玻色 - 爱因斯坦凝聚体中的暗孤子与无相互作用费米气体耦合而成的系统中的可控摩擦。费米子作为杂质原子，并非原始凝聚体的一部分，它们会从孤子上散射。我们研究了暗孤子的半经典动力学，暗孤子是一种具有负质量的类粒子物体，并计算了它的摩擦系数。令人惊讶的是，它周期性地依赖于种间（杂质 - 凝聚体）与种内（凝聚体 - 凝聚体）相互作用强度的比值。通过调整这个比值，可以进入摩擦系数消失的 regime。我们为负质量物体发展了一种随机动力学的一般理论，并发现它们的动力学与正质量物体的动力学截然不同：它们不会经历布朗运动。从精确的相空间概率分布函数（即位置和速度）中，我们发现孤子的轨迹和寿命都会因摩擦而改变，并且孤子只有在存在摩擦和限制势的情况下才会经历布朗运动。这些结果与艾科克 [《美国国家科学院院刊》，2503 (2017)] 在一个具有玻色杂质散射体的类似系统中的实验观测结果在定性上是一致的。
