Fermionic shock waves - dissipative or dispersive?

TL;DR

This paper investigates whether shock waves in ultracold Fermi gases are regularized by dissipation or dispersion, proposing experimental methods to distinguish between these mechanisms based on shock speed and collision dynamics.

Contribution

It introduces two experimental approaches to determine the shock regularization mechanism in fermionic gases, addressing the current ambiguity in experimental observations.

Findings

Proposes measuring shock speed to identify dissipation or dispersion.

Suggests observing 1D collisions with tight confinement for mechanism determination.

Highlights the challenge of resolving oscillations due to current imaging limitations.

Abstract

The collision of two clouds of Fermi gas at unitarity (UFG) has been recently observed to lead to shock waves whose regularization mechanism, dissipative or dispersive, is being debated. While classical, dissipative shocks, as in gas dynamics, develop a steep, localized shock front that translates at a well-defined speed, dispersively regularized shocks are distinguished by an expanding region of short wavelength oscillations with two speeds, those of the leading and trailing edges. For typical UFG experimental conditions, the theoretical oscillation length scale is smaller than the resolution of present imaging systems so it is unclear how to determine the shock type from its structure alone. Two experimental methods to determine the appropriate regularization mechanism are proposed: measurement of the shock speed and observation of a one-dimensional collision experiment with sufficiently tight radial confinement.