Abstract
We study the dynamics of a supersonically expanding, ring-shaped Bose-Einstein condensate both experimentally and theoretically. The expansion redshifts long-wavelength excitations, as in an expanding universe. After expansion, energy in the radial mode leads to the production of bulk topological excitations—solitons and vortices—driving the production of a large number of azimuthal phonons and, at late times, causing stochastic persistent currents. These complex nonlinear dynamics, fueled by the energy stored coherently in one mode, are reminiscent of a type of “preheating” that may have taken place at the end of inflation.
- Received 16 October 2017
- Revised 3 February 2018
DOI:https://doi.org/10.1103/PhysRevX.8.021021
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Synopsis
An Expanding Universe in the Lab
Published 19 April 2018
The rapid expansion of a Bose-Einstein condensate can mimic the expansion of the Universe.
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Popular Summary
Cosmological expansion is central to our understanding of the Universe. Our knowledge of this expansion is limited to what we can learn by observation because creating a universe in a laboratory is (understandably) a bit difficult. One potential laboratory stand-in for the Universe is an expanding Bose-Einstein condensate (BEC), an exotic state of ultracold matter where the wave functions of atoms overlap and the atoms behave as one. A BEC is a vacuum for phonons (quantized vibrations of matter or sound waves), much like the Universe is a vacuum for photons (quantized particles of light). Here, we experimentally explore these connections and find two common phenomena.
First, in both the Universe and our BEC, waves are redshifted to longer wavelengths and damped during expansion. Second, once the BEC’s expansion ceases, numerous phonons are created as energy added in the expansion process equilibrates. A qualitatively similar process occurred in the early Universe: After a rapid expansion period (known as inflation) ended, energy contained in the quantum field that drove the inflation decayed into lower-energy particles. In both cases, the result is reheating, an important process that presumably produced the high-temperature state of matter that preceded the formation of structure in the Universe.
These initial results lay the groundwork for an exciting new application of cold-atom physics: simulating quantum field processes in the early Universe.