Persistent Currents in Fermionic Quantum Gases

量子现象通常在微观尺度上最明显，但也有一些特殊的材料，量子效应在大尺度上很重要。这些材料通常具有非凡的特性，例如超导性，这使得它们对于配电，电磁铁，精密传感器和量子计算等各种应用非常重要。这些“超级”材料的多体量子物理学可能非常复杂，预测材料特性甚至物质的量子相的存在已经被证明是非常困难的。该奖项支持超冷原子的实验室量子模拟实验，这将提高我们对超流相形成机制的理解，以及它们在以不同方式受到干扰时的分解方式。这些实验将扩大目前的能力，创造，研究和理解物质的奇异量子相，这既是基本的科学兴趣，也是技术进步的重要因素。在这项研究计划中，超冷费米子原子（Li-6）将被限制在环形光学陷阱中，光学技术将用于在系统温度足够低时形成的费米子对超流体中产生持续电流。最初的目标是创建和研究持续电流在一个环形的分子BEC。研究人员将创建可旋转的约瑟夫森结来探测系统，并分析系统的特性作为相互作用强度，温度和有效维度的函数。然后，这些研究将扩展到包括强相互作用幺正极限中的持续电流，以及系统中可达到的温度所允许的BCS极限。这些实验的结果将进行分析，以提取有关超流临界速度，从声子介导的耗散对破坏激发，超流/冷凝分数的过渡信息，并以其他方式验证这个重要的超流参考系统的关键理论预测。在超流转变温度以上进行的测量将有助于解决最近在介观正常金属环中持续电流的实验观察所提出的问题。该计划还将为长期努力研究非常规超流体相的质量和自旋输运的低能极限奠定重要基础，这些超流体相的理解程度较低，和/或其存在尚未得到证实。

Quantum phenomena are generally most evident at microscopic scales, but there are some special materials where quantum effects are important at large scales. These materials often have extraordinary properties such as superconductivity that make them important for diverse applications such as electrical power distribution, electromagnets, precision sensors, and quantum computing. The many-body quantum physics of these "super" materials can be stunningly complex, and predicting material properties or even the existence of quantum phases of matter has proven to be surprisingly difficult. This award supports laboratory quantum simulation experiments with ultra-cold atoms that will improve our understanding of the mechanisms leading to the formation of superfluid phases, and the way they break down when disturbed in different ways. These experiments will expand present capabilities to create, study, and understand exotic quantum phases of matter that are both of fundamental scientific interest and important to the advancement of technology. In this research program, ultra-cold fermionic atoms (Li-6) will be confined to ring-shaped optical traps, and optical techniques will be used to create persistent currents in the superfluids of fermionic pairs which form when the system temperature is sufficiently low. The initial objective is to create and study persistent currents in a ring-shaped molecular BEC. The researchers will create rotatable Josephson junctions to probe the system and analyze the properties of the system as a function of interaction strength, temperature, and effective dimensionality. These studies will then be extended to include persistent currents in the strongly-interacting unitary limit, and as far into the BCS limit as permitted by the temperatures achievable in the system. The results of these experiments will be analyzed to extract information about the superfluid critical velocity, the transition from phonon-mediated dissipation to pair-breaking excitations, superfluid/condensate fractions, and otherwise validate key theoretical predictions for this important superfluid reference system. Measurements conducted above the superfluid transition temperature will help resolve questions raised by recent experimental observations of persistent currents in mesoscopic normal-metal rings. This program will also establish an essential foundation for longer-term efforts to study the low energy limits of mass and spin transport in unconventional superfluid phases that are less well understood, and/or whose existence has yet to be confirmed.