Interacting Atoms in Optical Lattices

摘要：量子力学技术应用的前沿涉及利用量子纠缠，其中粒子之间的详细相互作用是至关重要的。这些新兴技术包括量子模拟器、量子计算机和量子通信，以及量子传感器和量子时钟等旧量子技术的高级版本。推进这些技术需要理解封闭的“量子多体系统”的动力学，即包含许多相互作用的粒子的系统，量子力学在其中很重要。这项工作的目标是帮助开发这种动态的通用描述。研究人员将通过实验研究目前拥有最完整平衡理论描述的量子多体系统，一维气体，他们将超冷原子放入光学晶格（由激光制成的周期性结构）中。通过使这些气体脱离平衡，在纠缠主导动力学的情况下，他们可以清楚地测试新兴的理论方法。实验系统可以逐渐变得更加复杂，这样用于描述它们的理论就可以涵盖范围广泛的非平衡系统。最大的直接影响可能是我们对量子模拟器的可靠性和量子计算机的鲁棒性的理解。参与本实验的本科生和研究生在实验物理方面得到了全面的训练，为许多不同类型的实验工作做好了准备。技术观众摘要：PI和他的学生将对一维（1D）玻色气体进行一系列测量，这些气体由超冷的87Rb原子组成，这些原子被困在由二维光学晶格制成的二维管阵列中。这些相互作用的多体系统是可积的，这意味着它们具有大量额外守恒量的特征。实验通常包括使这些系统脱离平衡状态并研究随之而来的动力学。与一般的多体量子系统不同，一维气体的平衡性质可以精确计算。然而，计算它们的非平衡性质一直是一个挑战。最近发展起来的一种数值技术——广义流体力学（GHD），有望在一定近似范围内描述可积系统的动力学。GHD是基于对“速度”的局部分布的跟踪，“速度”是与可积系统中出现的准粒子相关的动量。这些重要但抽象的对象直到最近才被测量（由PI的团队），团队计划在更多样化的环境中测量它们。通过这些测量，我们将能够首次在有趣的中间和强耦合状态下对GHD进行定量测试。他们还将通过测量波函数猝灭后动量和速度分布的演变来研究GHD适用的边界。最后，他们建议将这些研究扩展到弱晶格中的一维气体，这是一个不可积系统，GHD也可能是一个有用的描述，至少在相对较短的时间内。在量子多体系统中寻找动力学的通用描述是一个重要的物理学前沿，而GHD有望提供其核心。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。

General audience abstract:The frontier of the technological application of quantum mechanics involves taking advantage of quantum entanglement, where the detailed interactions among particles are of central importance. Such emerging technologies include quantum simulators, quantum computers and quantum communication, as well as advanced versions of older quantum technologies like quantum sensors and clocks. Advancing these technologies requires understanding the dynamics of closed ‘quantum many-body systems,’ i.e. systems containing many particles which interact with each other and where quantum mechanics is important. The goal of this work is to help develop a universal description of such dynamics. The researchers will experimentally study the quantum many-body system that currently has the most complete equilibrium theoretical description, one-dimensional gases, which they make by putting ultracold atoms into optical lattices (periodic structures made from laser light). By taking these gases out of equilibrium, in situations where entanglement dominates dynamics, they can cleanly test emerging theoretical approaches. The experimental system can be made progressively more complex, so that the theories used to describe them can encompass a wide range of non-equilibrium systems. The largest immediate impact is likely to be in our understanding of the reliability of quantum simulators and the robustness of quantum computers. The training in experimental physics obtained by undergraduates and graduate students working on this experiment is comprehensive and is good preparation for many different types of experimental work.Technical audience abstract:The PI and his students will perform a series of measurements on one-dimensional (1D) Bose gases, which consist of ultra-cold 87Rb atoms trapped in a 2D array of tubes that are made with a 2D optical lattice. These interacting many-body systems are integrable, which implies that they are characterized by a large set of extra conserved quantities. The experiments generally involve taking these systems out of equilibrium and studying the ensuing dynamics. Unlike generic many-body quantum systems, the equilibrium properties of 1D gases can be calculated exactly. Their non-equilibrium properties, however, have been a challenge to calculate. A recently developed numerical technique, generalized hydrodynamics (GHD), promises to describe, to within certain approximations, the dynamics of integrable systems. GHD is based upon keeping track of the evolving local distribution of ‘rapidities’, which are the momenta associated with the quasiparticles that emerge in integrable systems. These important but abstract objects have only recently been measured (by the PI’s team) and the team plans to measure them in a much more diverse set of circumstances. With these measurements will come the ability to quantitatively test GHD for the first time in the interesting intermediate and strong coupling regimes. They will also study the border at which GHD becomes applicable, by measuring the evolution of momentum and rapidity distributions after a wavefunction quench. Finally, they propose to extend these studies to a 1D gas in a weak lattice, a non-integrable system for which GHD might also be a useful description, at least at relatively short times. The search for a universal description of dynamics in quantum many-body systems is an important physics frontier, and GHD holds the promise of providing its core.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.