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Arthur T Knackerbracket has found the following story:

Now, researchers at the National Institute of Standards and Technology (NIST) and their colleagues at the University of Maryland have developed a step-by-step recipe to produce the atomic-scale devices. Using these instructions, the NIST-led team has become only the second in the world to construct a single-atom transistor and the first to fabricate a series of single electron transistors with atom-scale control over the devices' geometry.

[...] Precise control over quantum tunneling is key because it enables the transistors to become "entangled" or interlinked in a way only possible through quantum mechanics and opens new possibilities for creating quantum bits (qubits) that could be used in quantum computing.

To fabricate single-atom and few-atom transistors, the team relied on a known technique in which a silicon chip is covered with a layer of hydrogen atoms, which readily bind to silicon. The fine tip of a scanning tunneling microscope then removed hydrogen atoms at selected sites. The remaining hydrogen acted as a barrier so that when the team directed phosphine gas (PH₃) at the silicon surface, individual PH₃ molecules attached only to the locations where the hydrogen had been removed (see animation). The researchers then heated the silicon surface. The heat ejected hydrogen atoms from the PH₃ and caused the phosphorus atom that was left behind to embed itself in the surface. With additional processing, bound phosphorous atoms created the foundation of a series of highly stable single- or few-atom devices that have the potential to serve as qubits.

Two of the steps in the method devised by the NIST teams—sealing the phosphorus atoms with protective layers of silicon and then making electrical contact with the embedded atoms—appear to have been essential to reliably fabricate many copies of atomically precise devices, NIST researcher Richard Silver said.

[...] "Because quantum tunneling is so fundamental to any quantum device, including the construction of qubits, the ability to control the flow of one electron at a time is a significant achievement," [researcher Jonathan] Wyrick said. In addition, as engineers pack more and more circuitry on a tiny computer chip and the gap between components continues to shrink, understanding and controlling the effects of quantum tunneling will become even more critical, Richter said.

Journal Reference:
Jonathan Wyrick, Xiqiao Wang, Ranjit V. Kashid, et al. Atom‐by‐Atom Fabrication of Single and Few Dopant Quantum Devices, Advanced Functional Materials (DOI: 10.1002/adfm.201903475)

Original Submission