Quantum Control and Entanglement in a Strongly Interacting Spin Ensemble

这项研究将使用冷却到接近绝对零度的超冷原子气体来研究量子相变。相变在宇宙学、粒子物理学和凝聚态物理学等许多物理学领域都扮演着重要的角色。水冻结成冰提供了一个熟悉的例子：当温度福尔斯冰点以下时，水分子的运动在结晶时经历相变。在宇宙学中，宇宙的大尺度结构被认为是大爆炸后不久宇宙通过相变（通过所谓的希格斯机制）冷却时形成的缺陷（例如“宇宙弦”）的遗迹。这项研究将探索量子相变和相关现象在一个未探索的制度在另一端的温标，接近绝对零度的开尔文温标（或近460度低于零的华氏温标）。这些实验将使用超冷原子玻色-爱因斯坦凝聚（一种在极低温度下形成的物质量子态）来探索相变，其中相变的行为由量子效应而不是热效应决定。 除了为多粒子系统的基础量子科学提供新的见解外，这些实验还可能应用于量子信息科学以及开发用于惯性制导和重力和磁场测量的新量子传感器。这项实验研究将研究玻色-爱因斯坦凝聚体中自旋为1的原子的强相互作用系综，以探索临界点附近量子相变的性质，并研究系综的非经典高度纠缠态的产生，控制和表征。研究使用仅包含单个自旋域的小型铷-87原子玻色-爱因斯坦凝聚体，使得动态演化仅发生在内部自旋自由度中。这些凝聚体的特点是一个良好的特点与可调的量子相变，允许探索铁磁和极性（极化）自旋基态的哈密顿量。一个完全可解的哈密顿量与量子相变的结合，以及量子机制中的动力学，提供了一个独特的工具组合来探索重要的课题，包括高精度的研究二阶量子相变，探索量子临界点上的激发，以及产生大规模纠缠态。 所有这些研究中的一个共同主题是有限尺寸效应在系统量子涨落中的作用。 这项研究将深入了解多粒子量子力学的基本原理，这些原理对物理学的许多领域都很重要，并将为量子多体自旋系统的未来探索指明方向，包括量子相变的热化和遍历性，哈密顿量子混沌和其他非线性现象的研究，以及有限温度效应。

This research will investigate quantum phase transitions using ultracold atomic gases cooled close to absolute zero temperature. Phase transitions play important roles in many areas of physics including cosmology, particle physics and condensed matter. The freezing of water to ice provides a familiar example: the motion of water molecules undergo a phase transition upon crystallization as the temperature falls below the freezing point. In cosmology, it is conjectured that the large scale structure of the universe is a vestige of defects (e.g. "cosmic strings") formed as the Universe cooled through a phase transition (via the so-called "Higgs mechanism") shortly after the Big Bang. This research will explore quantum phase transitions and associated phenomena in an unexplored regime at the opposite end of the temperature scale, close to absolute zero on the Kelvin temperature scale (or nearly 460 degrees below zero on the Fahrenheit temperature scale). The experiments will use ultracold atomic Bose-Einstein condensates (a quantum state of matter that forms at extremely low temperatures) to explore phase transitions in which the behavior of the transition is determined by quantum effects rather than thermal effects. In addition to providing new insight to the fundamental quantum science of many-particle systems, these experiments have potential applications to quantum information science and to the development of new quantum sensors for inertial guidance and measurement of gravity and magnetic fields. This experimental research will study strongly interacting ensembles of spin-1 atoms in a Bose-Einstein condensate to explore the nature of quantum phase transitions in the neighborhood of the critical point and to investigate creation, control and characterization of non-classical highly entangled states of the ensembles. The investigations use small rubidium-87 atomic Bose-Einstein condensates containing just a single spin domain, such that the dynamic evolution occurs only in the internal spin degrees of freedom. These condensates feature a well-characterized Hamiltonian with a tunable quantum phase transition that allow exploration of both ferromagnetic and polar (nematic) ground states of the spins. The combination of an exactly solvable Hamiltonian with a quantum phase transition together with demonstrated dynamics in the quantum regime provide a unique combination of tools to explore important topics including high precision studies of a second order quantum phase transitions, exploration of excitations across a quantum critical point, and the generation of massively entangled states. A common theme in all of these studies is the role of finite size effects that manifest in the quantum fluctuations of the system. This research will provide insight into fundamental principles of many-particle quantum mechanics that are important to many areas of physics and will point the way to future explorations of quantum many-body spin systems including thermalization and ergodicity crossing a quantum phase transition, investigations of Hamiltonian quantum chaos and other non-linear phenomena, and finite temperature effects.