Itty bitty engine puts a single atom to work

Heat engines, big and small, turn heat into mechanical work. The steam engine (left) pushes a piston that turns a wheel. A pint-sized version (right) sets an atom in motion to perform work.
ILLUSTRATIONS: J. HIRSHFELD; SOURCES: RACHEL CASIDAY AND REGINA FREY/WASHINGTON UNIV. IN ST. LOUIS; J. ROSSNAGEL, ET AL/ARXIV.ORG 2015