Less than one-half nemometer in size.

A team of physicists at the Technical University of Munich (TUM) have created in their laboratory what they believe to be the world's smallest molecular switch. In their experiment, the team was able to build a switch with an inner diameter of less than half a nanometer, making it making it the smallest atomic switching unit realized to date. It moves a single proton to one of four positions or states at speeds of up to 500 changes in state per second.

The experiment was a demonstration of switching on the molecular level. There is no immediate practical application. However, "to press a button four times, by moving a single proton in one molecule is," as Knud Seufert from TUM observed, "a real step towards technologies on the nanoscale."

The scientists published their results in the journal Nature Nanotechnology.