The extraction of work from hidden degrees of freedom

Key Points:

• Maxwell’s demon thought experiment links information about microscopic fluctuations to work extraction from a heat bath, formalized in information thermodynamics, which unifies work, entropy, and information in non-equilibrium systems.
• Traditional bounds on extractable work from measurement-based feedback (generalized second law) assume Markovian (memoryless) environments, but many real systems exhibit non-Markovian dynamics due to hidden environmental degrees of freedom (hDoFs) that store memory and influence system dynamics.
• Single-time measurements cannot access thermodynamically useful information about environmental memory, but repeated or time-delayed measurements can reveal information backflow from hDoFs, enabling enhanced work extraction beyond Markovian limits.
• Experimentally, an optically trapped colloidal particle in a viscoelastic fluid was used to demonstrate that two consecutive binary measurements separated by an optimal delay allow retrieval of information stored in environmental memory, leading to work extraction exceeding Markovian bounds.
• The study establishes that environmental memory constitutes a thermodynamic resource, and time-delayed measurements provide an operational method to harness this memory for improved information engines and feedback protocols in complex, correlated environments.