Experimental Extraction of Coherent Ergotropy and Its Energetic Cost in a Superconducting Qubit

TL;DR

This paper experimentally investigates how initial quantum coherence in a superconducting qubit influences work extraction, revealing optimal states for maximizing efficiency and demonstrating scalable coherence control in quantum thermodynamics.

Contribution

It introduces a method to control and optimize coherence-based work extraction in superconducting qubits, advancing quantum thermodynamic device development.

Findings

Coherence determines the partitioning of ergotropy.

Optimal initial states depend on dominant decoherence channels.

Energy costs are crucial for maximizing efficiency.

Abstract

Quantum coherence, encoded in the off-diagonal elements of a system's density matrix, is a key resource in quantum thermodynamics, fundamentally limiting the maximum extractable work known as ergotropy. While previous experiments have isolated coherence-related contributions to work extraction, it remains unclear how coherence can be harnessed in a controllable and energy-efficient manner. Here, we experimentally investigate the role of initial-state coherence in work extraction from a superconducting transmon qubit. By preparing a variety of pure states and implementing three complementary extraction protocols, we reveal how coherence governs the partitioning of ergotropy. We find that the choice of initial state depends on the dominant decoherence channel-energy relaxation or dephasing. By further accounting for thermodynamic costs, we identify optimal initial states that maximize the efficiency. Our results demonstrate that the initial-state design provides a scalable approach to coherence control and advances the development of efficient quantum thermodynamic devices.