# Quantum Signatures in the Quantum Carnot Cycle

## TL;DR

This paper explores quantum Carnot-like cycles that operate irreversibly with non-zero power, utilizing shortcuts to equilibrium and coherence effects, revealing quantum signatures and trade-offs between power and efficiency.

## Contribution

It introduces and compares three quantum Carnot-analog cycles employing shortcuts and coherence, highlighting quantum signatures and performance trade-offs.

## Key findings

- The Carnot-shortcut cycle shows a maximum power at an optimal cycle time.
- The Endo-global cycle exhibits positive power with quantum coherence effects.
- Quantum signatures are observed at short cycle times, indicating non-classical behavior.

## Abstract

The Carnot cycle combines reversible isothermal and adiabatic strokes to obtain optimal efficiency, at the expense of a vanishing power output. Quantum Carnot-analog cycles are constructed and solved, operating irreversibly at non-vanishing power. Swift thermalization is obtained in the isotherms utilizing a shortcut to equilibrium protocols and the adiabats employ frictionless unitary shortcuts. The working medium in this study is composed of a particle in a driven harmonic trap. For this system, we solve the dynamics employing a generalized canonical state. Such a description incorporates both changes in energy and coherence. This allows comparing three types of Carnot-analog cycles, Carnot-shortcut, Endo-shortcut and Endo-global. The Carnot-shortcut engine demonstrates the trade-off between power and efficiency. It posses a maximum in power, a minimum cycle time where it becomes a dissipator and for a diverging cycle time approaches the ideal Carnot efficiency. The irreversibility of the cycle arises from non-adiabatic driving, which generates coherence. To study the role of coherence we compare the performance of the shortcut cycles, where coherence is limited to the interior of the strokes, with the Endo-global cycle where the coherence never vanishes. The Endo-global engine exhibits a quantum signature at a short cycle-time, manifested by a positive power output while the shortcut cycles become dissipators. If energy is monitored the back action of the measurement causes dephasing and the power terminates.