# Collective performance of a finite-time quantum Otto cycle

## TL;DR

This paper investigates how collective quantum effects, including superradiance and phase transitions, influence the performance and power output of a finite-time quantum Otto cycle with a spin system as the working fluid.

## Contribution

It introduces a model of a quantum Otto cycle with collective spins, analyzing the impact of superradiance and quantum phase transitions on engine performance.

## Key findings

- Superradiant thermalization can enhance engine power.
- Quantum phase transitions can negatively affect cycle efficiency.
- Operational regimes can be distinguished by work output analysis.

## Abstract

We study the finite-time effects in a quantum Otto cycle where a collective spin system is used as the working fluid. Starting from a simple one-qubit system we analyze the transition to the limit cycle in the case of a finite-time thermalization. If the system consists of a large sample of independent qubits interacting coherently with the heat bath, the superradiant equilibration is observed. We show that this phenomenon can boost the power of the engine. Mutual interaction of qubits in the working fluid is modeled by the Lipkin-Meshkov-Glick Hamiltonian. We demonstrate that in this case the quantum phase transitions for the ground and excited states may have a strong negative effect on the performance of the machine. Reversely, by analyzing the work output we can distinguish between the operational regimes with and without a phase transition.