Autonomous quantum thermodynamics with a quantum kicked top reservoir

Area of Science:

• Quantum thermodynamics
• Quantum information science
• Statistical mechanics

Background:

• Characterizing energy exchange in quantum systems is crucial for understanding thermodynamics.
• Traditional approaches often rely on external driving or equilibrium assumptions.
• Finite quantum systems present unique challenges for defining heat and work.

Purpose of the Study:

• To develop an operational framework for quantifying energy exchange (heat and work) between a quantum system and a tunable environment.
• To explore the role of environmental dynamics, particularly chaos, in energy transfer.
• To investigate the impact of partial thermalization on quantum energy conversion protocols.

Main Methods:

• Modeling the environment using a quantum kicked top, a system with tunable dynamics from regular to chaotic.
• Defining heat and work via a weighted decomposition of reservoir energy change, using long-time fluctuations to quantify thermalization.
• Analyzing an Otto-like energy conversion protocol to assess efficiency and fluctuations.

Main Results:

• The framework allows continuous interpolation between coherent (worklike) and incoherent (heatlike) energy transfer.
• Increasing chaos in the quantum kicked top enhances effective thermalization and transforms energy flow from structured to stochastic.
• Both apparent efficiency and fluctuations in the Otto-like protocol are sensitive to reservoir dynamics.

Conclusions:

• Partial thermalization can serve as a resource in quantum energy conversion.
• The observed efficiency is an operational quantity dependent on specific environmental dynamics, not a strict thermodynamic bound.
• The developed framework offers a versatile tool for studying quantum thermodynamics in finite, non-equilibrium systems.