Understanding Phase Diffusion in Bose Einstein Condensates

[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?

 

[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’’.

 

[wdlang]

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’’.

Thanks a lot!

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

 

[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.