Joint Quantum Institute, National Institute of Standards and Technology and University of Maryland, Gaithersburg, Maryland 20899, USA.
Department of Physics, Georgia Southern University, Statesboro, Georgia 30460-8031, USA.
Nature. 2014 Feb 13;506(7487):200-3. doi: 10.1038/nature12958.
Atomtronics is an emerging interdisciplinary field that seeks to develop new functional methods by creating devices and circuits where ultracold atoms, often superfluids, have a role analogous to that of electrons in electronics. Hysteresis is widely used in electronic circuits-it is routinely observed in superconducting circuits and is essential in radio-frequency superconducting quantum interference devices. Furthermore, it is as fundamental to superfluidity (and superconductivity) as quantized persistent currents, critical velocity and Josephson effects. Nevertheless, despite multiple theoretical predictions, hysteresis has not been previously observed in any superfluid, atomic-gas Bose-Einstein condensate. Here we directly detect hysteresis between quantized circulation states in an atomtronic circuit formed from a ring of superfluid Bose-Einstein condensate obstructed by a rotating weak link (a region of low atomic density). This contrasts with previous experiments on superfluid liquid helium where hysteresis was observed directly in systems in which the quantization of flow could not be observed, and indirectly in systems that showed quantized flow. Our techniques allow us to tune the size of the hysteresis loop and to consider the fundamental excitations that accompany hysteresis. The results suggest that the relevant excitations involved in hysteresis are vortices, and indicate that dissipation has an important role in the dynamics. Controlled hysteresis in atomtronic circuits may prove to be a crucial feature for the development of practical devices, just as it has in electronic circuits such as memories, digital noise filters (for example Schmitt triggers) and magnetometers (for example superconducting quantum interference devices).
原子电子学是一个新兴的交叉学科领域，旨在通过创建设备和电路来开发新的功能方法，其中超冷原子（通常是超流体）的作用类似于电子在电子学中的作用。滞后现象在电子电路中被广泛应用——它在超导电路中经常被观察到，并且在射频超导量子干涉器件中是必不可少的。此外，它对于超流性（和超导性）与量子化的持久电流、临界速度和约瑟夫森效应一样基本。然而，尽管有多种理论预测，但在任何超流原子玻色-爱因斯坦凝聚体中都没有观察到滞后现象。在这里，我们直接检测到由超流玻色-爱因斯坦凝聚体环中的旋转弱连接（原子密度较低的区域）阻塞形成的原子电子学电路中量化循环状态之间的滞后现象。这与以前在超流液氦中的实验形成对比，在以前的实验中，在不能观察到流动量子化的系统中以及在显示出量化流动的系统中，直接观察到滞后现象。我们的技术允许我们调整滞后环的大小，并考虑伴随滞后的基本激发。结果表明，滞后涉及的相关激发是涡旋，并且表明耗散在动力学中起着重要作用。原子电子学电路中的受控滞后可能被证明是开发实用设备的关键特征，就像它在电子电路中（例如存储器、数字噪声滤波器（例如施密特触发器）和磁力计（例如超导量子干涉器件））一样。
