Physicists in Germany have taken mechanical miniaturization to the ultimate limit by producing a heat engine – one of the key inventions of classical thermodynamics – made of only one atom, and have measured its output. While microscale heat engines have been proposed and built in the past, this single-atom design is the smallest to date.
The heat engine, which converts a difference in temperature to mechanical work, is the archetypal machine of classical thermodynamics. The classical thermodynamic definition of temperature involves the average energy of a large number of particles, and is therefore not directly applicable to a single atom. However, a well-defined, classical thermodynamic temperature can still be obtained for such a particle, using the so-called ergodic theorem, which states that the average energy of a large number of particles in a region of space is equal to the energy of a single particle over a period of time. "That was a really tricky part of the design of the heat engine: how can you make use of the time-averaged definition of temperature?" explains lead researcher Kilian Singer of the University of Mainz.
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