We expand on our results on Brillouin cooling to reduce the thermal phonon population in waveguides by starting at cryogenic temperatures and reducing the effective mode temperature to 24.3 K. The paper can be found here.

Authors: Lisa Fischer, Laura Blázquez Martínez, Changlong Zhu, Robin Chenevière, Johann Troles, and Birgit Stiller

Abstract:
Thermal phonons are a major source of decoherence in quantum mechanical systems. Operating in the quantum ground state is therefore often an experimental prerequisite. Additionally, to passive cooling in a cryogenic environment, active laser cooling enables the reduction of phonons at specific acoustic frequencies. Brillouin cooling has been used to show efficient reduction of the thermal phonon population in waveguides at GHz frequencies down to 74 K. In this Letter, we demonstrate the cooling of a 7.608 GHz acoustic mode by combining Brillouin active cooling with precooling from 77 K using liquid nitrogen. We show a 69% reduction in the phonon population, resulting in a final temperature of 24.3 ± 1.9 K, 50 K lower than previously reported.