Wydział Fizyki, Uniwersytet w Białymstoku, Lipowa 41, 15-424 Białystok, Poland.
Phys Rev Lett. 2012 Nov 16;109(20):205302. doi: 10.1103/PhysRevLett.109.205302. Epub 2012 Nov 13.
We show that solitons occur generically in the thermal equilibrium state of a weakly interacting elongated Bose gas, without the need for external forcing or perturbations. This reveals a major new quality to the experimentally widespread quasicondensate state, usually thought of as primarily phase-fluctuating. Thermal solitons are seen in uniform 1D, trapped 1D, and elongated 3D gases, appearing as shallow solitons at low quasicondensate temperatures, becoming widespread and deep as temperature rises. This behavior can be understood via thermal occupation of the type II excitations in the Lieb-Liniger model of a uniform 1D gas. Furthermore, we find that the quasicondensate phase includes very appreciable density fluctuations while leaving phase fluctuations largely unaltered from the standard picture derived from a density-fluctuation-free treatment.
我们证明了，在弱相互作用的长玻色气体的热平衡状态中，会普遍出现孤子，而无需外部强制或干扰。这揭示了实验中广泛存在的准凝聚态的一个主要新特性，通常认为它主要是相位涨落。在均匀一维、囚禁一维和拉长三维气体中可以看到热孤子，在准凝聚态温度较低时呈现为浅孤子，随着温度升高变得广泛而深。这种行为可以通过在均匀一维气体的 Lieb-Liniger 模型中对 II 型激发的热占据来理解。此外，我们发现准凝聚相包括非常可观的密度涨落，同时基本保持了从无密度涨落处理中推导出的标准相位涨落图像。
