Enhanced heat flow in the hydrodynamic-collisionless regime

TL;DR

This paper investigates heat conduction in a cold atomic cloud with mixed hydrodynamic and collisionless regions, revealing unexpectedly high heat transfer due to high angular momentum atoms and identifying a standing wave sound mode.

Contribution

It demonstrates enhanced heat conduction in an anisotropic trap and uncovers the role of high angular momentum atoms in heat transfer.

Findings

Large heat conduction observed compared to homogeneous case

High angular momentum atoms contribute significantly to heat transfer

Identification of a standing wave sound mode

Abstract

We study the heat conduction of a cold, thermal cloud in a highly asymmetric trap. The cloud is axially hydrodynamic, but due to the asymmetric trap radially collisionless. By locally heating the cloud we excite a thermal dipole mode and measure its oscillation frequency and damping rate. We find an unexpectedly large heat conduction compared to the homogeneous case. The enhanced heat conduction in this regime is partially caused by atoms with a high angular momentum spiraling in trajectories around the core of the cloud. Since atoms in these trajectories are almost collisionless they strongly contribute to the heat transfer. We observe a second, oscillating hydrodynamic mode, which we identify as a standing wave sound mode.