# Dissipation in mesoscale superfluids

## TL;DR

This paper analyzes the maximum flow speed of superfluids through narrow channels, focusing on dissipation mechanisms like vortex nucleation, and presents a universal framework for different superfluid systems.

## Contribution

It introduces a universal approach to understanding critical velocities in superfluids considering vortex nucleation and phase slips across various conditions.

## Key findings

- Critical velocity decreases sharply in ultra-narrow channels.
- Universal scaling laws for superfluid flow across different systems.
- Thermal vortex nucleation limits superfluid flow at small scales.

## Abstract

We investigate the maximum speed at which a driven superfluid can flow through a narrow constriction with a size on the order of the healing length. Considering dissipation via the thermal nucleation of quantized vortices, we calculate the critical velocity for superfluid $^4$He and ultracold atomtronic circuits, identify fundamental length and velocity scales, and are thus able to present results obtained in widely different temperature and density ranges in a universal framework. For ultra-narrow channels we predict a drastic reduction in the critical velocity as the energy barrier for flow reducing thermally activated phase slip fluctuations is suppressed.