[Reeses]

2 nanometers is 4 atoms of silicon wide. At what point do they call it a quantum computer?

[Yardstick]

2 nanometers is 4 atoms of silicon wide.
~~~~~~~~~~~~~~
That is incredible.

[takebackaustin]

It is closer to four silicon unit cells, ( the repeat distance in Si crystals) which is a little different, but still mind boggling.

All semiconductor based computers are based on applied quantum mechanics. Transistors are based on bandgaps, Fermi level, all that. So in that sense the answer is, always.

But really, “Quantum computer” is a term of art, a machine computing using states which are superpositions (qubits). In that sense, they cannot shrink a conventional computer and make a quantum computer, so the answer is never.

Good question that makes you think!

[SauronOfMordor]

In silicon, inter-atom spacing is .235 no, so more like 10 atoms. Still, we are very rapidly approaching physical limits.

https://www.princeton.edu/~maelabs/mae324/glos324/silicon.htm#:~:text=The%20electronic%20configuration%20of%20the,neighbor%20distance%20is%200.235%20nm.