Expansion Dynamics and Prethermalization in Ultracold Quantum Gases

一般来说，科学的进步，尤其是物理学的进步，有很多种形式。通常，对意外现象的实验观察，如高温超导，会引发新理论的发展。有时“思想实验”也会产生新的理论，比如广义相对论，这些理论后来会在实际实验中得到验证。在超冷量子气体领域，通过超高真空（等离子体的超冷对应物）的磁场捕获温度处于纳米开尔文状态的气体，实验和理论发展经常齐头并进。对超冷量子气体的实验推动了最近统计物理学的许多发展。他们还以极高的准确性检验了理论预测。该项目涉及PI的理论小组与美国和欧洲的实验小组之间的密切合作。目标是开发和测试越来越复杂的非平衡量子系统的理论描述，同时有助于开发和测试越来越精确和可控的实验平台。在这个奖项下，研究生将接受量子物理和计算物理方面的培训（例如，他们将为超级计算机编写和运行代码）。PI将在当地高中讲授有关实验和理论发展的讲座，以激励学生从事STEM职业。PI将研究远离平衡态的超冷一维（1D）气体的量子动力学，以及它们在一维中的膨胀动力学。在1D中经过长时间的膨胀后，后者的动力学使得实验测量速度分布成为可能，这是PI和宾夕法尼亚州立大学小组最近合作测量的长期思考的“理论结构”。这些新研究的一个中心目标将是检验最近发展起来的广义流体动力学理论（GHD），并确定需要在理论上解释的GHD之外的修正。第二个要探索的主题是具有弱破碎可积性（更一般地说，弱破碎守恒定律）的系统的动力学，以实验测试最近发展的预热化理论，并寻找其适用性的限制。这里的中心目标将是开发理论/实验工具来预测/测量广泛系统中的热化率。此外，PI的小组将发展最近引入的理论方法的推广，以研究不可穿透的SU(N)费米子的平衡和非平衡动力学，并将研究可积相互作用哈密顿子本征态中可观测的非对角矩阵元素，以了解它们可以教给我们关于量子动力学和接近可积的输运的知识。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Progress in science in general, and physics in particular, comes in many flavors. Often experimental observations of an unexpected phenomenon, such as high-temperature superconductivity, trigger the development of new theories. It also happens sometimes that "thought experiments" result in new theories, such as general relativity, that are later tested in actual experiments. In the field of ultracold quantum gases, gases at temperatures that are in the nano-Kelvin regime trapped by means of magnetic fields in ultrahigh vacuum (the ultracold counterpart of plasmas), experimental and theoretical developments often go hand in hand. Experiments with ultracold quantum gases have motivated many recent developments in statistical physics. They have also tested theoretical predictions with an exceptional accuracy. This project involves a close collaboration between the theoretical group of the PI and experimental groups in the US and Europe. The goal is to develop and test increasingly sophisticated theoretical descriptions of nonequilibrium quantum systems while contributing to the development and testing of progressively more accurate and controllable experimental platforms. Under this award, graduate students will be trained in quantum physics and computational physics (e.g., they will write and run codes for supercomputers). The PI will deliver lectures about the experimental and theoretical developments at the local high school to motivate students to pursue careers in STEM. The PI will study the quantum dynamics of ultracold one-dimensional (1D) gases locally far from equilibrium, as well as their expansion dynamics in 1D. After long expansion times in 1D, the latter dynamics enables the experimental measurement of rapidity distributions, long-thought "theoretical constructs" that were recently measured in a collaboration between the PI and groups at Penn State. A central goal of the new studies will be to test the recently developed theory of generalized hydrodynamics (GHD), and to identify corrections beyond GHD that need to be accounted for theoretically. A second topic to be explored is the dynamics of systems with weakly broken integrability (and, more generally, weakly broken conservation laws) to experimentally test a recently developed theory of prethermalization, and to search for its limits of applicability. A central goal here will be to develop theoretical/experimental tools to predict/measure thermalization rates in a broad range of systems. In addition, the PI's group will develop generalizations of a recently introduced theoretical approach to study equilibrium and far-from-equilibrium dynamics of impenetrable SU(N) fermions, and will study the off-diagonal matrix elements of observables in the eigenstates of integrable interacting Hamiltonians to understand what they can teach us about quantum dynamics and transport close to integrability.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.