Hacker News Reader

Comment by imglorp | Hacker News Reader

Isn't there a little law of thermodynamics here about doing work and dissipating energy?

To be clear, there is some dissipation with magnons, just a lot less than Joule heating. But exciting a magnon will heat up your sample, because magnons don't live forever and decay after some time. That energy has to go somewhere.

Reversible computers avoid this by producing arbitrarily little entropy

How do you deal with all the output "garbage" signals that reversible computing produces? Do they all get sent somewhere, and the place where they get sent to discards them but heats up?

From my recollection of the Feynman lectures on the subject, basically yes. Nevertheless the overall theoretical efficiency is still considerably higher than an irreversible machine.

It’s not an area where I’ve followed the subsequent research though. I’d be delighted if someone who knows more chimed in. There are also some obvious advantages for being able to choose precisely when you do a reset and generate your waste heat.

Being able to choose where you want do dissipate heat would be a game changer in itself

The garbage output signals get recycled indefinitely. Only the useful output ever needs to generate heat.

It was thought for some time that they needed be turned to heat, but that's actually untrue. Using quantum gates, it is possible to do an arbitrary classical computation and recycle the anciliary bits.

Neat! Any reference you could share for me to read more?

There is a short but sufficient Wikipedia article on it - it is called uncomputation : https://en.wikipedia.org/wiki/Uncomputation?wprov=sfla1

The textbook I used in my quantum computing class dealt with the subject far better, but unfortunately it's not public yet :/

Reply on news.ycombinator.com