Superconductor ICs: Computing without transistors (2000) (spectrum.ieee.org)

With all of the excitement around the intersection of superconductors and computing, it is interesting to note that the "popular" families of superconducting logic don't use transistors at all. Rapid Single Flux Quantum (RSFQ) uses Josephson junctions and quanta of magnetic flux in loops to spit out millivolt-high, picosecond-long pulses, with the presence of a pulse being a logic 1 and the absence being a zero (rather than voltages being logic level as in CMOS). Other resources include:

http://www.physics.sunysb.edu/Physics/RSFQ/Projects/WhatIs/r...

And the challenges of EDA with RSFQ:

https://www.youtube.com/watch?v=3O6GpFCIxv0