Do un-entangled photons exist?

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Discussion Overview

The discussion revolves around the existence of un-entangled photons in quantum mechanics, particularly in the context of wave function collapse and entanglement with measurement apparatuses. Participants explore the implications of photon entanglement and the potential for photons to become un-entangled after measurement events.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants propose that after a measurement event, a photon becomes un-entangled from its twin photon, but question whether it simultaneously becomes entangled with another part of the universe or experimental apparatus.
  • Others argue that the photon is typically entangled with the measurement apparatus, suggesting that if the twin photon has not been detected, entanglement persists between the apparatus and the partner photon.
  • A participant presents two hypotheses regarding the timing of entanglement: (a) the photon becomes entangled with the apparatus upon detection and loses its entanglement with its twin, or (b) the photon is already entangled with the apparatus and becomes dis/un-entangled upon detection.
  • One participant supports the second hypothesis, stating that the entanglement between the two photons remains intact even if one photon is destroyed, with subsequent entanglement occurring between the remaining photon and the measurement apparatus.

Areas of Agreement / Disagreement

Participants express differing views on the nature of photon entanglement and the implications of measurement, indicating that multiple competing perspectives remain without a clear consensus.

Contextual Notes

The discussion involves assumptions about the nature of wave function collapse and the definitions of entanglement and un-entanglement, which may not be universally agreed upon.

San K
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in the various QM experiments:

after select event(s) have occurred, we assume collapse of wave function and the photon becomes un-entangled from its twin.

however does this un-entangled photon almost simultaneously get entangled with some other part of existence/universe/experimental apparatus?

is there any such thing as being un-entangled?
 
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San K said:
in the various QM experiments:

after select event(s) have occurred, we assume collapse of wave function and the photon becomes un-entangled from its twin.

however does this un-entangled photon almost simultaneously get entangled with some other part of existence/universe/experimental apparatus?

is there any such thing as being un-entangled?

Usually we would say the photon is entangled with the apparatus used to measure it, and had the other photon not been detected yet, entanglement between the apparatus and partner photon would exist.
 
StevieTNZ said:
Usually we would say the photon is entangled with the apparatus used to measure it, and had the other photon not been detected yet, entanglement between the apparatus and partner photon would exist.

thanks StevieTNZ, are you suggestion b (not a) below?

a) the photon gets entangled with the apparatus upon detection and looses its entanglment with its twin photon

b) the photon is already entangled with the apparatus and get dis/un-entangled upon detection
 
Yes, I would be going with (b).

The entanglement between the two photons (A and B), although a photon has been destroyed, has not been broken. Thereafter, entanglement exists between photon B and the apparatus used to measure photon A.
 

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