# Quantum theory of friction

1. Jan 27, 2008

### Loren Booda

Recently, macroscopic friction has been explained at the quantum level. Can you give a simple synopsis of how atomic forces act to create such nonconservative systems?

2. Jan 28, 2008

### MeChaState

Hi,
I think the best way to imagine an nonconservative system is to use the interference and using just few springs with particle hanging on them. if they are coupled and become excited with an external harmonic force the respond will be harmonic and easy to average over time and space. If the external force is not matching the eigenfrequency of Atomic systems, it will cause kind of wave that over the time and space is nonconservative.
Light the fire Inside!
David

3. Jan 28, 2008

### Loren Booda

I was thinking of an application for the wavefunction which I had seen alluded to in the past five years (Discover magazine?) I am interested in a modern quantum mechanical explanation of friction.

Your model is somewhat helpful, David, but I was hoping more for a reference to a paper or abstract with QM. By the way, how could a system relying solely on spring constants be nonconservative? Should there not be a damping factor?

4. Jan 28, 2008

### f95toli

I can't give you a reference but I know there has been a lot of work done on force measurements and nanoidentation using SPM. This is presumably as close as you can actually get to "microscopic" friction with quantum effects.
As far as I understand this is every difficult to model since the atoms on the surface (and the SPM tip) will always always try to rearrange themselves to minimize the energy. Hence, it is not possible to make "simple" models and the only way forward is to use "brute force" DFT calculations on large number of atoms (how large depends upon how good you supercomputer is, the more the better).

I know that John Pethica has done a lot of work in this field, his name might be a good starting point in Google Schoolar.

5. Jan 28, 2008

### MeChaState

Hi Loren,
Sorry for misunderstanding of what you want and sorry for the my limited english. Regarding the question of "nonconservative" system of couples springs, I think averaging over a period of oscillation can make it nonconservative. It is after my understanding always a question of averaging. I use the springs model to imagine the QM and it helps me always. The damping is exactly what I mean equivalent to friction. An oscillation without damping can be like an.
Take care
David

6. Jan 28, 2008

### ZapperZ

Staff Emeritus
Can you please provide a source for this? You should know by now that things like this require a reference source.

Zz.

7. Jan 28, 2008

### Loren Booda

Here is a simple and fairly elegant, but perhaps flawed, foray into quantum friction.

http://www.qcaustralia.org/Publications/2006/Barnett_Jeffers_Cresser.pdf"

"In our theory, this [phenomenon] arises as a consequence of treating individual collisions as simultaneous measurements of the Brownian particle’s position and momentum."

Do simultaneous measurements of particle position and momentum sound like quantum mechanics to you? Do they bring uncertainty into their equations?

Last edited by a moderator: Apr 23, 2017
8. Jan 28, 2008

### Loren Booda

Continued...

"5. Conclusion

The classical theory of friction does not transfer in any simple way into the quantum
regime. This is a problem for the emerging quantum information processing technologies
in which environmentally induced decoherence is a key factor in limiting both performance
and scalability. Our approach to describing friction is, in a sense, based on ideas in quantum
information theory in that it emphasizes the role of measurement, of information extraction, on the dynamics of the particle..."

9. Jan 29, 2008

### Andy Resnick

Really? this is news to me. Please provide a reference.

Edit: never mind, ZapperZ beat me to this.....

Last edited: Jan 29, 2008
10. Jan 29, 2008

### Andy Resnick

Actually, on page 409, section 5 (Conclusion), the authors state "The classical theory of friction does not transfer in any simple way into the quantum regime".

Also, the problem considered by the authors is actually Brownian motion, and not "macroscopic friction", or the type we associate with sliding. And they do not have any insight on the origin of the friction coefficient $\gamma$.