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

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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.