A universal recipe for extracting work without knowing the state
Usually you can only extract the maximum work from a system if you know exactly what state it is in. A 2026 result shows that, surprisingly, you need not.
Work, information and free energy
In thermodynamics the most work you can draw from a system, reversibly, is set by its free energy — and in the quantum case that free energy depends on the system's state. The textbook recipe for reaching the bound therefore assumes you already know the state, so you can tailor a reversible protocol to it. That assumption is exactly what a Maxwell's demon trades on: it measures, learns the state, and converts what it learns into work.
One protocol for every input
The new work constructs a single quantum process — fixed in advance, the same for every input — that still extracts work equal to the free energy of whatever unknown state it is handed. The process does not depend on a prior measurement of the state, yet it does not leave the reversible bound on the table. It is a sharper statement of how tightly information and extractable work are bound together, and of how close to thermodynamic reversibility a well-designed quantum operation can run.
Results like this sit directly under the Institute's reading of reversibility: the closer a process comes to reversible, the less it wastes, whether the currency is heat, information or usable work.
Source
Watanabe & Takagi, “Universal work extraction in quantum thermodynamics”, Nature Communications, 2026. For the foundations, see our physics of information reading list.