Failure of local thermal equilibrium in quantum friction

TL;DR

This paper demonstrates that the common assumption of local thermal equilibrium in non-equilibrium quantum systems fails for quantum friction, significantly underestimating the drag force and highlighting the need for revised theoretical models.

Contribution

It reveals the breakdown of local thermal equilibrium assumptions in quantum friction, emphasizing the importance of correlations in non-equilibrium quantum systems.

Findings

Local thermal equilibrium underestimates quantum friction force by about 80%.

Correlations in driven quantum systems invalidate local thermal assumptions.

Revisiting non-equilibrium models is necessary for accurate quantum friction descriptions.

Abstract

Recent progress in manipulating atomic and condensed matter systems has instigated a surge of interest in non-equilibrium physics, including many-body dynamics of trapped ultracold atoms and ions, near-field radiative heat transfer, and quantum friction. Under most circumstances the complexity of such non-equilibrium systems requires a number of approximations to make theoretical descriptions tractable. In particular, it is often assumed that spatially separated components of a system thermalize with their immediate surroundings, although the global state of the system is out of equilibrium. This powerful assumption reduces the complexity of non-equilibrium systems to the local application of well-founded equilibrium concepts. While this technique appears to be consistent for the description of some phenomena, we show that it fails for quantum friction by underestimating by approximately $80 \%$ the magnitude of the drag force. Our results show that the correlations among components of driven, but steady-state, quantum systems invalidate the assumption of local thermal equilibrium, calling for a critical reexamination of this approach for describing the physics of non-equilibrium systems.