# Effects of noise-induced coherence on the fluctuations of current in quantum absorption refrigerators

## TL;DR

This paper studies how noise-induced coherence affects current fluctuations in a quantum absorption refrigerator, revealing differences between classical and quantum regimes especially near maximum current conditions.

## Contribution

It provides an analytical model explaining current behavior in quantum and classical regimes, highlighting the impact of non-uniqueness and phase transition-like behavior.

## Key findings

- Quantum fluctuations are moderate away from critical points.
- Classical fluctuations become large near maximum current.
- System behavior near critical points resembles a first-order phase transition.

## Abstract

We investigate the effects of noise-induced coherence on average current and current fluctuations in a simple model of quantum absorption refrigerator with degenerate energy levels. We describe and explain the differences and similarities between the system behavior when it operates in the classical regime, where the populations and coherences in the corresponding quantum optical master equation decouple in a suitably chosen basis, and in the quantum regime, where such a transformation does not exist. The differences between the quantum and the classical case are observable only close to the maximum current regime, where the system steady-state becomes non-unique. This allows us to approximate the system dynamics by an analytical model based on a dichotomous process, that explains the behavior of the average current both in the classical and in the quantum case. Due to the non-uniqueness, the scaled cumulant generating function for the current at the vicinity of the critical point exhibits behavior reminiscent of the dynamical first-order phase transition. Unless the system parameters are fine-tuned to a single point in the parameter space, the corresponding current fluctuations are moderate in the quantum case and large in the classical case.