Are quantum computers required to be cold to reduce Brownian motion?

[iVenky]

I understand that based on what I have read online quantum computers are required to be close to absolute zero because it introduces less error. Is it because brownian motion due to thermal agitation of molecules reduces with temperature?

 

[DrClaude]

Not Brownian motion, simply thermal motion. In the solid state case, it is the coupling of the qubit with thermal phonons.

 

[iVenky]

Not Brownian motion, simply thermal motion. In the solid state case, it is the coupling of the qubit with thermal phonons.

Isn't thermal motion similar to Brownian motion?

This is the thermal noise we are talking about, right?

 

[DrClaude]

Isn't thermal motion similar to Brownian motion?

Brownian motion usually implies the motion of a particle embedded in some medium, see https://en.wikipedia.org/wiki/Brownian_motion

This is the thermal noise we are talking about, right?

Yes.

 

[iVenky]

Brownian motion usually implies the motion of a particle embedded in some medium, see https://en.wikipedia.org/wiki/Brownian_motion
Yes.

Ok, thanks but thermal motion is a subset of Brownian motion, right?

 

[DrClaude]

Ok, thanks but thermal motion is a subset of Brownian motion, right?

No, the other way around. Brownian motion could be seen as one type of thermal motion.

 

[f95toli]

Isn't thermal motion similar to Brownian motion?

This is the thermal noise we are talking about, right?

It depends on the type of quantum computer. For ion trap based quantum computer you need the trapped ion to be "cold" (which btw is somewhat difficult concept when you are talking about single particles) to reduce the number of "motional quanta".
In solid state systems "thermal motion" can indeed be a problem (because it can generate excitations, e.g. quasiparticles), but mostly it is about reducing the number of "hot" photons that can reach your qubit.

Overall, I would say that it is better to think about the need for cooling as as way to reduce the amount of energy that can "leak" into your system (via photons or phonons) and unintentionally cause excitations.