Does getting which-way info introduce a phase difference?

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Discussion Overview

The discussion revolves around the concept of whether obtaining which-way information in quantum experiments introduces a phase difference or causes decoherence between wave functions. It also explores the implications of erasing which-way information on restoring coherence.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants question whether which-way information introduces a phase difference or leads to decoherence between the wave functions involved.
  • One participant argues that obtaining which-way information fundamentally alters the quantum state, comparing the scenarios of having no information (superposition) versus having information (definite state).
  • Another participant mentions the specific context of phase differences between two entangled photons in two-photon interference, suggesting a more complex interaction.
  • There is a claim that which-way information is typically associated with dual-slit experiments, where only one photon is present at a time, implying a lack of entanglement in that scenario.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between which-way information and phase differences, with no consensus reached on whether obtaining such information leads to decoherence or how it affects entangled states.

Contextual Notes

Participants do not clarify the specific definitions of phase difference or coherence in this context, and there are unresolved assumptions regarding the nature of the quantum states involved.

San K
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does getting which-way info introduce a phase difference (or cause de-coherence) between both the "waves"?

and does erasure of which-way information restore coherence?
 
Last edited:
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a difference from what?

the 'which-way' information completely changes the state, like the slits be 1 and 2, then you have 1+2 without any information, then 1 OR 2 with information
you can't phase change your way between (1+2),(1),(2)
 
genericusrnme said:
a difference from what?

the 'which-way' information completely changes the state, like the slits be 1 and 2, then you have 1+2 without any information, then 1 OR 2 with information
you can't phase change your way between (1+2),(1),(2)

forgot to mention, sorry...

phase difference between two entangled photons (two-photon interference)
 
Which way information usually referes to dual-slit type experiments, there's only one photon there at anyone time so there is no enganglement.
 

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