The theory of thermodynamics has taught us how to harness the abundant and disordered energy that exists all around us as heat and how to convert it to useful energy in the form of work. For example, we can burn fuel to make the wheels of our cars turn. This understanding helped build the machines of the Industrial Revolution, which forever changed our societies and place in the world. Another revolution is occurring at the nanoscale, where researchers are busy making nanomachines for a host of applications, such as targeted drug delivery and green-energy storage.

But how efficiently can we extract energy from a hot environment? The typical tool we use is a heat engine, which allows heat to flow from a hot bath to a colder one, extracting work in the process. In 1824, Carnot showed that the maximum efficiency of a heat engine is given by the ratio of the temperature of the two baths [1]. Jan Klaers and colleagues [2] at the Swiss Federal Institute of Technology (ETH) in Zurich have, for the first time, experimentally demonstrated that, by engineering the properties of the environment, they can drive a nanoscale engine twice as efficiently as Carnot predicted. This will allow synthetic nanoengines to operate more efficiently than their macroscopic counterparts.

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