Specific type of Josephson junction. Probably can be made tiny and in huge numbers through photolithography.
Figure 1.
Illustration of a thin-film superconducting tunnel junction (STJ)
. Source. The superconducting material is light blue, the insulating tunnel barrier is black, and the substrate is green.
Video 1.
Quantum Transport, Lecture 14: Josephson effects by Sergey Frolov (2013)
. Source. youtu.be/-HUVGWTfaSI?t=878 mentions maskless electron beam lithography being used to produce STJs.

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