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Large work extraction and the Landauer limit in a continuous Maxwell demon


The relation between entropy and information dates back to the classical Maxwell demon paradox1, a thought experiment proposed in 1867 by James Clerk Maxwell to violate the second law of thermodynamics. A variant of the classical Maxwell demon is the Szilard engine, proposed by Leo Szilard in 19291. In it, at a given time, the demon observes the compartment occupied by a single molecule in a vessel and extracts work by operating a pulley device. Here, we introduce the continuous Maxwell demon, a device capable of extracting arbitrarily large amounts of work per cycle by repeated measurements of the state of a system, and experimentally test it in single DNA hairpin pulling experiments. In the continuous Maxwell demon, the demon monitors the state of the DNA hairpin (folded or unfolded) by observing it at equally spaced time intervals, but it extracts work only when the molecule changes state. We demonstrate that the average maximum work per cycle that can be extracted by the continuous Maxwell demon is limited by the information content of the stored sequences, in agreement with the second law. Work extraction efficiency is found to be maximal in the large information-content limit where work extraction is fuelled by rare events.

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Fig. 1: Classical MD versus CMD.
Fig. 2: Single-molecule tests for the classical MD and CMD.
Fig. 3: Extracted work distributions.

Data availability

The data that support the plots within this paper and other findings of this study are available from the authors upon reasonable request.


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We acknowledge financial support from grants 308850 INFERNOS, 267862 MAGREPS (FP7 EU programme) FIS2013-47796-P, FIS2016-80458-P (Spanish Research Council) and ICREA Academia prize 2013 (Catalan government). M.R.-C. has received funding from the EU Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement no. 749944.

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M.R.-C. performed the experiments. F.R. performed the theoretical calculations. Both authors planned the research and contributed to data analysis and preparation of the manuscript.

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Correspondence to F. Ritort.

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Ribezzi-Crivellari, M., Ritort, F. Large work extraction and the Landauer limit in a continuous Maxwell demon. Nat. Phys. 15, 660–664 (2019).

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