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Updated: Aug 2, 2025

Cooling an Optically Trapped Ultracold Fermi Gas by Periodical Driving
Published on: March 30, 2017
Ultrafast nonequilibrium dynamics of rotons in superfluid helium
Alexander A Milner1, Philip C E Stamp1,2,3, Valery Milner1
1Department of Physics & Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada.
Abstract:
Short-time dynamics of superfluids far from equilibrium remains largely unknown, despite its importance for key processes in these systems. Here, we describe a method for locally perturbing the density of superfluid helium via the excitation of roton pairs with ultrashort laser pulses. By measuring the time dependence of this perturbation, we track the nonequilibrium dynamics of the two-roton states on femtosecond and picosecond timescales. Our results reveal an ultrafast equilibration of roton pairs as they thermalize with the colder equilibrium quasiparticle gas. Future applications of this technique to different temperature and pressure regimes, in various superfluids, will enable to probe rapid nucleation and decay processes, as well as metastable Bose-Einstein condensates of rotons and roton pairs.
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