Entropy transport through a superfluid quantum point contact: A Keldysh field-theory approach

TL;DR

This paper models matter and entropy transport through a superfluid quantum point contact using Keldysh field theory, extending previous particle current studies to include entropy and comparing with cold atom experiments.

Contribution

It introduces a Keldysh formalism approach to compute both particle and entropy currents in a superfluid junction, including entropy oscillations at low voltage.

Findings

Entropy current oscillates at low voltage in ballistic limit.

The model agrees with experimental data in the unitary Fermi gas regime.

Extended understanding of entropy transport in superfluid quantum contacts.

Abstract

We study the matter and entropy transport between two ultra-cold neutral Fermi-gas reservoirs linked by a quantum point contact under a chemical-potential gradient. We describe the two leads with a BCS mean-field model and derive the current-bias characteristics for both particle and entropy transport. We compute the out of equilibrium steady-state currents by using the Keldysh formalism. In accordance with previous works in the literature, we confirm the well-known behavior for the particle current and extend the computation to the entropy current in the BCS regime. The entropy current shows an oscillatory behavior at low voltage in the ballistic junction limit. We analyze the results for a wide range of values of the junction's transparency. We also compare our findings with experimental results in cold atomic gases in the unitary regime.