Laboratory for studying tunneling times and tailored potentials for atoms with tunable interactions

量子力学基本上构成了所有现代物理学的基础，它在一定程度上以其预言而闻名，这些预言经常挑战我们对物理世界的经典直觉。其中最具典型性的可能是被称为“量子隧道”的现象，在这种现象中，量子粒子穿越了一种传统上无法逾越的障碍。近一个世纪以来，人们对量子隧道现象已经有了很好的了解，它在光合作用和核聚变等自然过程以及扫描隧道显微镜、磁力计和超导量子比特等实用设备中都扮演着关键角色。然而，自20世纪30年代以来，隧道施工过程的持续时间一直存在争议。我们的团队最近测量了原子在由精确聚焦的激光束创建的势垒区域内停留的时间，这是近20年艰苦工作的顶峰。但这打开了有关隧道效应的更深层次问题的大门，实际上也是关于广泛的原子-光相互作用的问题。更重要的是，原子也相互作用；我们已经看到证据表明，这些碰撞显著改变了从我们的屏障反射的云的行为。这些相互作用的性质令该领域的专家们感到惊讶，因为它们出人意料地依赖于原子的自旋；进一步的研究将阐明关于强相互作用量子多体系统的重要问题。为了实现这些，也为了对反射原子在势垒中停留的时间进行可靠的测量，我们建议使用原子(39K)进行实验，它具有方便地可调的相互作用强度。对更广泛的量子测量理论具有影响的一个特别重要的目标是比较势垒子区域的隧道和反射时间：本质上，询问传输和反射的粒子他们把时间花在了哪里。除此之外，我们将发展研究具有任意形状和随时间变化的势的粒子的量子相互作用的能力。具体地说，正如我们在初步实验中所展示的那样，双势垒电势可以作为输出是超冷的过滤器。模拟表明，这种冷却过程可以使我们的温度比有史以来最低的温度低几个数量级，从而打开了一种新的超冷原子物理制度的大门。为了研究非相互作用或强相互作用原子的隧道效应，我们必须有必要的激光能够捕获和冷却可以调节其相互作用的原子物种。此外，为了研究空间分辨隧穿时间、相互作用辅助隧穿或使用双势垒冷却，我们需要产生比我们现在所能产生的更窄的势垒的能力。要做到这一点，我们将需要定制的物镜来聚焦光线，以及一个定制的腔室，以允许这些实验所需的更高水平的光学访问。

Quantum mechanics, which underlies essentially all of modern physics, is in part known for its predictions that frequently challenge our classical intuitions about the physical world. Perhaps the most paradigmatic of these is the phenomenon known as `quantum tunneling' in which a quantum particle traverses a barrier that is classically insurmountable. Quantum tunneling has been well understood for nearly a century, and is known to play a key role in both natural processes such as photosynthesis and nuclear fusion as well as practical devices like the scanning tunneling microscope, magnetometers, and superconducting qubits. However, the duration of the tunneling process has remained controversial since the 1930s. Our group recently measured how long atoms spend within a barrier region created by a tighly focused laser beam, in the culmination of nearly two decades of hard work. But this opens the door to deeper questions about tunneling, and in fact about a broad range of atom-light interactions.  Importantly, atoms also interact with one another; we have seen evidence that these collisions significantly modify the behavior of clouds reflected from our barrier. The nature of these interactions surprised experts in the field, because of an unexpected dependence on the spin of the atoms; further studies will elucidate important questions about strongly interacting quantum many-body systems. In order to achieve these, and also to carry out reliable measurements of the time reflected atoms spend in the barrier, we propose experiments with atoms (39K) which possess a conveniently tunable interaction strength. A particularly important goal with implications for quantum measurement theory more broadly is to compare tunneling and reflection times for sub-regions of the barrier: essentially, to ask transmitted and reflected particles where they spent their time. Beyond this, we will develop the ability to study the quantum interaction of particles with potentials of arbitrary shape and time-dependence. In particular, a double-barrier potential can act as a filter whose output is ultracold, as we demonstrated in a preliminary experiment. Simulations have shown this cooling process can take us orders of magnitude colder than the coldest temperature ever achieved, opening the door to a new regime of ultracold atomic physics. In order to study tunneling with non-interacting or strongly interacting atoms, we must have the necessary lasers capable of trapping and cooling an atomic species which can have its interactions tuned. Furthermore, to study spatially resolved tunneling times, interaction assisted tunneling, or cooling using a double barrier potential we will need the ability to generate much narrower barriers than we are capable of right now. To do this we will need custom made objective lenses for focusing the light as well as a custom chamber that will allow for the increased level of optical access required for these experiments.