Midlands Ultracold Atom Research Centre, School of Physics & Astronomy, University of Nottingham, Nottingham, NG7 2RD, United Kingdom.
5. Physikalisches Institut and Center for Integrated Quantum Science and Technology, Universität Stuttgart, 70569, Stuttgart, Germany.
Sci Rep. 2017 Aug 22;7(1):9070. doi: 10.1038/s41598-017-08941-8.
Superfluidity and superconductivity have been widely studied since the last century in many different contexts ranging from nuclear matter to atomic quantum gases. The rigidity of these systems with respect to external perturbations results in frictionless motion for superfluids and resistance-free electric current flow in superconductors. This peculiar behaviour is lost when external perturbations overcome a critical threshold, i.e. above a critical magnetic field or a critical current for superconductors. In superfluids, such as liquid helium or ultracold gases, the corresponding quantities are a critical rotation rate and a critical velocity respectively. Enhancing the critical values is of great fundamental and practical value. Here we demonstrate that superfluidity can be completely restored for specific, arbitrarily large flow velocities above the critical velocity through quantum interference-induced resonances providing a nonlinear counterpart of the Ramsauer-Townsend effect occurring in ordinary quantum mechanics. We illustrate the robustness of this phenomenon through a thorough analysis in one dimension and prove its generality by showing the persistence of the effect in non-trivial 2d systems. This has far reaching consequences for the fundamental understanding of superfluidity and superconductivity and opens up new application possibilities in quantum metrology, e.g. in rotation sensing.
从上世纪开始，人们就在许多不同的背景下广泛研究了超流性和超导性，从核物质到原子量子气体。这些系统对外部干扰的刚性导致超流体无摩擦运动和超导体无电阻电流流动。当外部干扰超过临界阈值时，这种特殊行为就会丢失，例如对于超导体来说，就是超过临界磁场或临界电流。在超流体（如液氦或超冷气体）中，相应的量分别是临界旋转率和临界速度。提高这些临界值具有重要的基础和实际价值。在这里，我们通过量子干涉诱导共振证明，在超过临界速度的特定、任意大的流速下，超流性可以完全恢复，从而为普通量子力学中发生的拉姆齐-汤森效应提供了一种非线性对应物。我们通过在一维中的彻底分析说明了这种现象的鲁棒性，并通过在非平凡的二维系统中展示该效应的持久性，证明了它的普遍性。这对于深入理解超流性和超导性具有深远的影响，并为量子计量学等领域的新应用开辟了可能性，例如在旋转感测方面。
