Engineered Three-Body Interactions in Quantum-Degenerate Atomic Gases

从最基本的角度来说，对我们周围世界的物理描述似乎需要两个要素：基本粒子和基本粒子对之间的相互作用。例如，光子，光的基本粒子，可以从单个电子散射，带电的电子会通过库仑力相互排斥。即使是包含许多基本粒子的物体似乎也会成对地相互作用。例如，原子之间的散射，有许多质子、中子和电子，通常用它们对之间的相互作用来描述。在更大的尺度上，月球、地球和太阳的运动可以用它们之间的万有引力来描述。月球、地球或太阳的构成无关紧要。然而，这项工作将侧重于三体相互作用的研究，这些相互作用不仅仅是成对相互作用的总和，而是当三个体中的一个被移除时效果为零的相互作用，并检查它们对世界物理描述的影响。该项目将培养一名马里兰大学的研究生。学生将接触到量子物理学的基础和实用水平。靠近当地的原子物理实验室，包括联合量子研究所和NIST，也将大大有利于学生。在原子、分子和光学物理学中，有几种情况下，三体相互作用是已知的。例如，在描述相互作用、反应和分子碰撞时，当积分出快速电子运动时，这种力出现在所谓的玻恩-奥本海默近似中。在核物理学中，三原子的叶菲莫夫态现在用超冷原子在纳米开尔文量级的温度下进行研究。这些弱束缚态的结合关键取决于所谓的三体参数。在所有情况下，当高能模式或快速成分从描述中“消除”时，三体相互作用就会出现。该小组将设计或制造多体系统，这些系统由超冷原子或分子组成，这些原子或分子保持在激光产生的周期势中，仅通过三体力相互作用。更准确地说，从原子通过成对相互作用进行相互作用的哈密顿量开始，研究人员将推导出只包含三体相互作用的有效哈密顿量。自由调节周期性捕获势以及两粒子相互作用强度的能力将是至关重要的。对这种有效的多体汉密尔顿理论的研究有两个不同的原因。首先，研究解决了关于三体力的起源或出现的基本问题。此外，首次有可能创建具有可控两体力的现实系统，从而突出三体力的作用。设计这种哈密顿量的第二个智力优点是，它们可能具有具有独特顺序的量子基态或相。例如，它可以导致具有原子对的超流体。这种方法依赖于两体相互作用的贡献之间的可控抵消，只留下三体相互作用。此外，它依赖于单粒子光学晶格势的随时间变化和驱动来填充能级子集，其能量模拟三体相互作用。这将对其他物理领域产生影响，在这些领域中，有效场论和集体现象是很重要的，比如凝聚态物理和高能物理。特别是，在原子系统中，人们可以研究那些基本的过程，但在这些领域所研究的系统中却远远无法接近。

At its most fundamental the physical description of the world around us seems to require two ingredients: elementary particles and interactions between pairs of such particles. For example, photons, the elementary particle of light, can scatter from a single electron and charged electrons will repel each other via the Coulomb force. Even objects that contain many elementary particles seem to interact in pairs. The scattering between atoms, with their many protons, neutrons, and electrons, for example, is often described in terms of interactions between pairs of them. At a bigger scale the motion of the moon, earth, and sun is describable in terms of the gravitational attraction between pairs of them. The composition of the moon, earth, or sun does not matter. This work, however, will focus on the study of three-body interactions, those that are not simply the sum of the pair-wise interactions, but those whose effect is zero when one of the three bodies is removed, and examine their influence on the physical description of the world. This project will train a University of Maryland graduate student. The student will be exposed to quantum physics at a fundamental yet practical level. The proximity to local atomic-physics laboratories, including the Joint Quantum Institute and NIST, will also greatly benefit the student.In atomic, molecular, and optical physics, there are several cases where three-body interactions are known to matter. For example, in the description of interacting, reacting, and colliding molecules, such forces arise in the so-called Born-Oppenheimer approximation when integrating out the fast electron motion. Conceived in nuclear physics, tri-atomic Efimov states are now studied with ultra-cold atoms at temperatures on the order of a nanoKelvin. Binding of these weakly-bound states crucially depends on a so-called three-body parameter. In all cases three-body interactions emerge when high-energy modes or fast constituents are "eliminated" from the description. This group will design or engineer many-body systems of ultra-cold atoms or molecules held in laser-generated periodic potentials that solely interact through three-body forces. More precisely, starting from a Hamiltonian, where atoms do interact through pair-wise interactions, the investigators will derive effective Hamiltonians that only contain three-body interactions. The ability to freely adjust the periodic trapping potential as well as the strength of the two-particle interactions will be crucial. Research into such effective many-body Hamiltonians has intellectual merit for two separate reasons. Firstly, the research addresses fundamental questions about the origin or emergence of three-body forces. Moreover, for the first time it may be possible to create a realistic system with controllable two-body forces and thereby highlight the role of three-body forces. A second intellectual merit of a design of such a Hamiltonian is that they might have quantum ground states or phases with unique order. For example, it can lead to superfluids with pairs of atoms. This approach relies on controllable cancellations between contributions to the two-body interaction, leaving only three-body interactions. In addition, it relies on time-dependent changes in and driving of the single-particle optical-lattice potential to populate a subset of levels, whose energies simulate three-body interactions. There will be impact in other fields of physics where effective field theories and collective phenomena are important, such as condensed matter and high-energy physics. In particular, with atomic system one can study processes that are fundamental but far-less accessible in systems investigated by those fields.