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Description
The ability to measure the stochastic degrees of freedom of a thermal system enables the extraction of energy from an equilibrium heat bath. This is the underlying principle of Maxwell’s demon and subsequent information engines [1, 2]. This apparent thermodynamics paradox is resolved when accounting for the energetic cost of the associated information processing and these novel engines are consistently described by the framework of information thermodynamics. Within this frame, it offer new possibilities to control fluctuations as well as energy and information flows through sub-parts of a system. For example, some biological processes at the microscopic scale, such as kinesin cargo-transport use information engine-like mechanism to improve their efficiency [3].
In this work, we experimentally realize a microscopic information engine configured as a compressible piston containing a thermalized colloidal suspension [4]. The particle positions are recorded to identify when a predefined region near the wall is empty, allowing the piston to compress the colloidal suspension without applying work on the system. We find that the mean compression energy $W$ stored is universally set by the probability of a positive measurement outcome by $W = -k_{\rm B} T p_1 \ln(p_1)$ where $p_1$ in turn is controlled by parameters such as density and compression step size. We further demonstrate that mechanical work can be extracted during the decompression of the piston, thereby closing the engine’s operating cycle. This brings information engine closer to biological system, with a full work-producing cycle at the level of thermal fluctuations.
[1] J. M. R. Parrondo, J. M. Horowitz, and T. Sagawa, Thermodynamics of information, Nature Physics 11, 131 (2015).
[2] R. Goerlich, L. Hoek, O. Chor, S. Rahav, and Y. Roichman, Experimental realizations of information engines: beyond proof of concept, Europhysics Letters 149, 61001 (2025).
[3] T. Ariga, K. Tateishi, M. Tomishige, and D. Mizuno, Noise-induced acceleration of single molecule kinesin-1, Physical review letters 127, 178101 (2021).
[4] R. Goerlich, G Pollack, E. Flaxer, S. Rahav and Y. Roichman Piston-Like Information Engine I: Universal Features in Equilibrium arXiv:2512.01942 (2025)