Bounds on skewness and kurtosis of steady state currents

TL;DR

This paper establishes bounds on skewness and kurtosis of steady state currents across various systems, providing tools to infer microscopic dynamics and system properties from fluctuation measurements.

Contribution

It derives and conjectures bounds on third and fourth current cumulants for multiple classes of transport systems, linking fluctuation properties to underlying physics.

Findings

Bounds on skewness and kurtosis are applicable to diverse systems.

Violations of bounds reveal information about interactions and network topology.

Current fluctuation measures can infer microscopic dynamics even at equilibrium.

Abstract

Current fluctuations are a powerful tool to unravel the underlying physics of the observed transport process. This work discusses some general properties of the third and the fourth current cumulant (skewness and kurtosis) related to dynamics and thermodynamics of a transport setup. Specifically, several distinct bounds on these quantities are either analytically derived or numerically conjectured, which are applicable to: 1) noninteracting fermionic systems, 2) noninteracting bosonic systems, 3) thermally driven classical Markovian systems, 4) unicyclic Markovian networks. Finally, it is demonstrated that violation of the obtained inequalities can provide a broad spectrum of information about the physics of the analyzed system, e.g., enable one to infer the presence of interactions or unitary dynamics, unravel the topology of the Markovian network, or characterize the nature of thermodynamic forces driving the system. In particular, relevant information about the microscopic dynamics can be gained even at equilibrium when the current variance -- a standard measure of current fluctuations -- is determined mostly by the thermal noise.