We propose a definition of externally measurable quantum work in driven systems. Work is given as a quantum observable on a control device which is forcing the system and can be determined without knowledge of the system Hamiltonian ${\widehat{H}}_{\mathcal{S}}$. We argue that quantum work fluctuation theorems which rely on the knowledge of ${\widehat{H}}_{\mathcal{S}}$ are of little practical relevance, contrary to their classical counterparts. Using our framework, we derive a fluctuation theorem which is operationally accessible and could in principle be implemented in experiments to determine bounds on free energy differences of unknown systems.

• Received 21 March 2020
• Revised 14 August 2020
• Accepted 10 September 2020

DOI:https://doi.org/10.1103/PhysRevResearch.2.033508

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society