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

量子力学基本上是所有现代物理学的基础，它的预言经常挑战我们对物理世界的经典直觉。也许其中最典型的是被称为“量子隧穿”的现象，在这种现象中，量子粒子穿过经典上无法逾越的障碍。量子隧穿已经被很好地理解了近世纪，并且已知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发挥关键作用。然而，自20世纪30年代以来，隧道过程的持续时间一直存在争议。我们的研究小组最近测量了原子在一个由紧密聚焦的激光束形成的势垒区域内停留的时间，这是近二十年努力工作的成果。但这为更深层次的隧穿问题打开了大门，事实上，这涉及到广泛的原子与光的相互作用。 重要的是，原子也会相互作用;我们已经看到证据表明，这些碰撞会显着改变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感到惊讶，因为它们对原子自旋的依赖性出乎意料;进一步的研究将阐明有关强相互作用量子多体系统的重要问题。为了实现这些目标，并进行可靠的测量反射的原子花费在屏障中的时间，我们提出了实验与原子（39 K）具有方便的可调相互作用强度。对量子测量理论有更广泛影响的一个特别重要的目标是比较势垒子区域的隧穿和反射时间：本质上，询问透射和反射粒子在哪里度过了时间。除此之外，我们还将培养研究具有任意形状和时间依赖性的粒子的量子相互作用的能力。特别是，双势垒可以作为一个过滤器，其输出是超冷的，正如我们在初步实验中所证明的那样。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，为超冷原子物理学的新制度打开了大门。为了研究非相互作用或强相互作用原子的隧穿，我们必须有必要的激光器能够捕获和冷却原子物种，可以调整其相互作用。此外，为了研究空间分辨的隧穿时间，相互作用辅助隧穿，或使用双势垒的冷却，我们将需要产生比我们现在能够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聚焦的光，以及一个定制的腔室，将允许增加这些实验所需的光学访问水平。

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.