What is ''phase diffusion''?

1. Mar 20, 2008

wdlang

in literatures, people are discussing about the phase diffusion of a bose einstein condensate

what does it mean?

the phase of the bec drifts on the unit circle randomly?

does this concept come from quantum optics?

2. Mar 21, 2008

lazybird

A classical, phase-coherent state is a superposition of many different Fock states (or number states). Now, due to the presence of atom-atom interaction in the condensates, each Fock state has different phase evolution rate. Therefore, a superposition state will have a spread of evolution rates, leading to ‘‘phase diffusion’’.

Last edited: Mar 21, 2008
3. Mar 21, 2008

wdlang

Thanks a lot!

However, this effect is named as 'collapse and revival' as i understand.

4. Mar 21, 2008

lazybird

Sure. You're right. Except in experiments with BEC, you don't get to see the revival part due to decoherences from other sources. For example, let's say you split a single BEC into two phase-coherent BECs. These two independent (yet initially coherent) condensates now will go through the "phase diffusion" that you mentioned. Before they have a chance to "rephase", though, other decoherence mechanisms (such as relative motion of the condensates) can totally erase the phase relationship, hence no revival.