[grondilu]

> OTOH I think there are theoretical lower bounds on the amount of energy that needs to be ejected as heat from a non-reversible computation, such that a non-reversible SC would still need to produce some heat.

Yes, it's called Landauer's principle, but it's so low it can be ignored for most intent and purposes.

[grahamrow]

Certain flavors of superconducting digital logic (there are a handful) such as AQFP (adiabatic quantum flux parametron) actually get close to the Landauer limit (with cooling power excepted). Interconnect (as some comments have noted) and lack of a good memory technology are the challenges for all these architectures.

[karma_pharmer]

In grad school I extrapolated the charts showing joules per bit of computation, looked at where it intersected the landauer limit compared to my own lifespan, and immediately lost interest in adiabatic computation. No regrets yet.