Understanding Phase Diffusion in Bose Einstein Condensates

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Discussion Overview

The discussion centers on the concept of phase diffusion in Bose-Einstein condensates (BECs), exploring its implications, underlying mechanisms, and related phenomena such as collapse and revival. Participants examine the nature of phase coherence and the effects of atom-atom interactions within the condensate.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions the meaning of phase diffusion in BECs, suggesting it may involve random drifting of phase on a unit circle and inquires about its origins in quantum optics.
  • Another participant explains that phase diffusion arises from the presence of atom-atom interactions in BECs, leading to different phase evolution rates for various Fock states in a superposition, resulting in a spread of evolution rates.
  • A later reply acknowledges the explanation but introduces the term "collapse and revival," indicating a potential connection between these concepts.
  • Another participant clarifies that while collapse and revival are relevant, experimental observations of revival are often hindered by decoherence from other sources, which can erase the phase relationship before rephasing occurs.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between phase diffusion and collapse and revival, with some agreeing on the mechanisms of phase diffusion while others highlight the complications introduced by decoherence. The discussion remains unresolved regarding the full implications of these phenomena.

Contextual Notes

Limitations include the dependence on specific definitions of phase coherence and the effects of decoherence mechanisms, which are not fully explored in the discussion.

wdlang
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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?
 
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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:
lazybird said:
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.
 
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.
 

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