In the ever-shrinking world of electronics, vacuum tubes long ago gave way to solid-state component transistors, then to transistors in integrated circuits. Last year an international team achieved the next astonishing milestone in downsizing: They devised a way to make a single-atom transistor, the smallest possible electronic switch. By controlling electrons, that atom can modulate the flow of information and so be the foundation of a new kind of ultrafast, ultracompact computer. The team was led by physicist Michelle Simmons of the University of New South Wales and electrical engineer Gerhard Klimeck of Purdue University.

The single-atom transistor is made by carving a slot in a hydrogen-coated silicon wafer with a tunneling electron microscope and depositing a single phosphorus atom in the hole. The phosphorus atom acts as an electrical bucket, holding one electron—representing a single bit of information—until it is jolted with an external voltage. The phosphorus switch has been tested and in the future could form the basis for both traditional and quantum computing.