Phase transitions and thermodynamic cycles in the broken PT-regime

TL;DR

This paper introduces a novel quantum thermodynamic cycle that surpasses classical efficiency limits, existing only in the low-temperature broken PT-symmetry phase of a non-Hermitian system, with implications for entropy and phase transitions.

Contribution

It presents a new quantum cycle with higher efficiency than Carnot, specific to the broken PT-regime in non-Hermitian quantum systems, highlighting phase transition effects.

Findings

Cycle efficiency exceeds Carnot limit in broken PT-regime

Cycle exists only at low temperatures in the broken PT phase

Entropy vanishes throughout the broken PT-regime

Abstract

We propose a new type of quantum thermodynamic cycle whose efficiency is greater than the one of the classical Carnot cycle for the same conditions for a system when viewed as homogeneous. In our model this type of cycle only exists in the low temperature regime in the spontaneously broken parity-time-reversal (PT) symmetry regime of a non-Hermitian quantum theory and does not manifest in the PT-symmetric regime. We discuss this effect for an ensemble based on a model of a single boson coupled in a non-Hermitian way to a bath of different types of bosons with and without a time-dependent boundary. The cycle can not be set up when considering our system as heterogeneous, i.e. undergoing a first order phase transition. Within that interpretation we find that the entropy is vanishing throughout the spontaneously broken PT-regime.