Most superconducting logic families aren't using transistors at all. They use Josephson junctions, which are just two pieces of superconductor separated by a non-supercondutor. RSFQ (Rapid Single Flux Quantum) uses millivolt-high picosecond-long pulses to represent logic 1 and their absence as logic zero, instead of using voltage level as in CMOS.

https://ieeexplore.ieee.org/document/783712 (770 GHz toggle flip-flop in 1999)

https://www.physics.sunysb.edu/Physics/RSFQ/Projects/WhatIs/...

Sooo, a 770 GHz processor? Do I understand it correctly? Jesus.

If using that flip-flop, whole processor will be closer to 100ghz (typically there are multiple transistors which need to stabilise before you have a result of computation). But probably those superconductors could enable even faster transistors and maybe we could get 1THz processors.

Like IDE ribbon cables gave way to sleek SATA cables, we could have another parallel to serial transition from silicon multicore crap to superconducting single core.

No, you'll get superconducting multicore because all that will happen is that the bloat will expand to consume the new cycle budget. This has already happened many times.

I'm looking forward to Chromium version 4201337 needing 20% of my 1Thz CPU to render simple text.

We'll get superconducting multicore because as a first step everyone will just map what they already know to the new space. Which is fun.

I suspect you'd still need very low temperatures to make this work, even with a high temperature superconductor: low temperatures reduce thermal noise, which may be an issue at such time scales (unless you pump a lot of energy per bit, which means high voltages (limits scaling) or current/capacitances (also limits scaling).

Are you aware of any obvious issues with manufacturing Josephson junctions using photolithography? Like, would switching to an LK-99 or similar set us back to the 70s in terms of wafer density/size?

You might be interested is this video, which talks about the EDA issues for RSFQ logic:

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

...and...

https://en.wikipedia.org/wiki/Josephson_junction_count

I don’t think we’d necessarily have to use it for transistors, but could use it in place of the metal interconnect that is significant in terms of resistive loss.

I think Josephson junctions. Also maybe you could eliminate copper loss by using LK-99 interconnect layers.

Well you can apparently make diodes with them: https://scitechdaily.com/mit-develops-superconducting-device...