Information engines move beyond proof of concept
Maxwell's demon began as a thought experiment about whether information could be turned into work. A 2025 review argues that its experimental descendants — "information engines" — have matured from curiosities into real devices that operate close to the fundamental thermodynamic limits.
From thought experiment to laboratory
An information engine, in the spirit of Maxwell's demon and the Szilard engine, extracts useful work from a heat bath by measuring a system and feeding the result back into how the system is driven. The review surveys a range of physical realisations: colloidal particles in optical traps, single electrons, semiconductor quantum dots and superconducting qubits. Across these platforms, measured information is converted into work in a way that is fully consistent with the second law once the cost of handling that information is included.
Approaching the Landauer bound
What marks the recent generation of experiments is their efficiency. Several now operate close to the Landauer reversible bound of kT ln 2 per bit, the minimum dissipation associated with manipulating information. Quantum-dot engines, in particular, use optimized fast-driving protocols to extract work efficiently without sacrificing the gains promised by feedback, narrowing the gap between idealised theory and practical hardware.
The experimental frontier
Taken together, these results make information engines the experimental frontier of the information–thermodynamics link. They turn long-standing questions about Maxwell's demon into measurable engineering targets, and they probe just how close real devices can come to the reversible limit set by Landauer's principle.
Source: review on arXiv:2501.13593; quantum-dot information engine on arXiv:2412.06916.