Gravitational caustics in an atom laser

M E Mossman,Michael Mcneil Forbes,T M Bersano,P Engels

doi:10.1038/s41467-021-27555-3

M E Mossman, Michael Mcneil Forbes + Show 2 more

Open Access

https://doi.org/10.1038/s41467-021-27555-3

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Abstract

Typically discussed in the context of optics, caustics are envelopes of classical trajectories (rays) where the density of states diverges, resulting in pronounced observable features such as bright points, curves, and extended networks of patterns. Here, we generate caustics in the matter waves of an atom laser, providing a striking experimental example of catastrophe theory applied to atom optics in an accelerated (gravitational) reference frame. We showcase caustics formed by individual attractive and repulsive potentials, and present an example of a network generated by multiple potentials. Exploiting internal atomic states, we demonstrate fluid-flow tracing as another tool of this flexible experimental platform. The effective gravity experienced by the atoms can be tuned with magnetic gradients, forming caustics analogous to those produced by gravitational lensing. From a more applied point of view, atom optics affords perspectives for metrology, atom interferometry, and nanofabrication. Caustics in this context may lead to quantum innovations as they are an inherently robust way of manipulating matter waves.

Highlights

Discussed in the context of optics, caustics are envelopes of classical trajectories where the density of states diverges, resulting in pronounced observable features such as bright points, curves, and extended networks of patterns
Catastrophe atom optics—the formation of caustics by atom trajectories—has previously been discussed in specific settings, for example in the context of atoms being released from a magnetooptical trap[27,28], atoms diffracting from a one-dimensional optical lattice[29,30], or expanding Bose-Einstein condensates (BECs) with spatially varying initial phase[31]
The pronounced half-ring-shaped caustic appearing for sufficiently strong repulsive potentials would not exist without the influence of gravity, and a similar feature would be difficult to see with light outside of cosmological contexts

Summary

Introduction

Discussed in the context of optics, caustics are envelopes of classical trajectories (rays) where the density of states diverges, resulting in pronounced observable features such as bright points, curves, and extended networks of patterns. We generate caustics in the matter waves of an atom laser, providing a striking experimental example of catastrophe theory applied to atom optics in an accelerated (gravitational) reference frame. While caustics and catastrophe theory have been used to characterize the atom laser itself, in particular in terms of its transverse beam profile[47,48,49,50], here we exploit the atom laser as a source of flow interacting with external potentials to generate a broad variety of caustic features These features include individual fold and cusp caustics, and even complex caustic networks. Atom optics differs from terrestrial light optics in a variety of ways, including the ability to introduce attractive as well as repulsive potentials, the power to perform internal state manipulation, e.g., for fluid flow tracing, and the ability to study non-negligible effects of gravity. In contrast to previous work, the use of an atom laser combined with external potentials and an adjustable effective

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