“But this device is perfect,” Michelle Simmons, a group leader and director of the ARC Centre for Quantum Computation and Communication at the University of New South Wales, said in a statement. “This is the first time anyone has shown control of a single atom in a substrate with this level of precise accuracy.”

In the 1950s, the physicist Richard P. Feynman predicted a world where there would be “plenty of room at the bottom,” opening new vistas into engineering disciplines that would use individual atoms as bricks and mortar in fields as diverse as computing and biology.

Since then, computer designers have moved ever closer to the smallest components that are possible to fabricate. Now, with the publication of the New South Wales and Purdue research, the scientists said they had shown the fundamental limits to which the components of silicon-based computers would be able to shrink in the future. Currently, the smallest dimension in state-of-the-art computers made by Intel is 22 nanometers — less than 100 atoms in diameter.

If the semiconductor industry remains on its current pace, it might be possible to reach that limit within two decades, Dr. Klimeck noted.

The scientists placed the single phosphorus atom using a device known as a scanning tunneling microscope. They used it to essentially scrape trenches and a small cavity on a surface of silicon covered with a layer of hydrogen atoms. Phosphine gas was then used to deposit a phosphorus atom at a precise location, which was then encased in further layers of silicon atoms.

While offering astounding precision for research, these microscopes are not currently applicable as manufacturing tools to make chips that contain billions or even trillions of transistors. Moreover, the devices now operate at very low temperatures.

Despite these limits, the semiconductor industry has made great progress in finding ways to build circuits that are far smaller than the wavelength of visible light. And recently, equipment makers have begun making it possible to assemble layers in silicon chips a single atom at a time.