Is there any upper bound on current fluctuation in cross-transport beyond linear response regime?

TL;DR

This paper investigates whether upper bounds on current fluctuations in cross-transport systems hold beyond the linear response regime, finding that such bounds are generally violated in nonequilibrium stationary conditions.

Contribution

The study demonstrates that previously established bounds on current fluctuations do not extend beyond the linear response regime, providing counterexamples and challenging existing assumptions.

Findings

Upper bounds are violated in nonequilibrium conditions.

Two examples demonstrate the absence of bounds beyond linear response.

No universal upper limit exists for current fluctuations outside linear response.

Abstract

Input and output current fluctuations in stationary cross-transport systems with two kinds of currents are investigated. In Saryal {\it et al.} [Phys. Rev. Lett. 127, 190603 (2021)], upper bounds on input and output current fluctuations are proven in the linear response regime and suggested the validity beyond the linear response regime. We examine these bounds beyond the linear response regime and find that these bounds are violated in general nonequilibrium stationary conditions. We show two examples to demonstrate the violation. Through these examples, we argue that no upper bound on input and output current fluctuations exist beyond the linear response regime.