How Would Afshar's Experiment Affect Entanglement?

In summary, Afshar's experiment involved sending a light beam through a double-slit to get interference, adding wires to the dark fringes, and then using a lens to "image" the two slits. The question was raised about the potential breakage of entanglement if one beam from an entangled source was sent through the experiment. It was suggested that momentum entanglement would likely be broken, but path entanglement and polarization entanglement could potentially remain intact. However, it was noted that the addition of wires in the usual place would result in the measurement of the photon in a different basis, downgrading the entanglement between the two photons into correlation.
  • #1
Erik Ayer
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4
TL;DR Summary
If one of the two beams from non-colinear SPDC were sent through Afshar's experiment, would momentum, path, and/or polarization entanglement be broken?
Afshar's experiment (https://en.wikipedia.org/wiki/Afshar_experiment) sent a light beam through a double-slit to get interference, put wires in the places where there were dark fringes, then refocused the light with a lens get "image" the two slits. I'm wondering what entanglements would break if one beam from an entangled source were sent through Afshar's experiment. To keep this slightly simple, assume the two beams with entangled photons are from type 2 SPDC and are not colinear - they two beams go in different directions.

What I would expect is that momentum entanglement would be broken when the beam went through the slits and diffracted. However, I wonder whether it could be preserved if, instead of slit, the beam were split with a regular old (non-polarizing) beam splitter and the two sub-beams made to overlap and interfere with a lens. My guess would be that path entanglement would survive since a photon going through the left slit would end up in the left image and one going through the right slit would end up in the right image after the lens. Polarization entanglement would survive since Afshar's experiment does nothing to measure or collapse the polarization state of superposition.
 
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  • #2
The dark spots that you'd put the wires in will not be present when the photon is entangled with another photon. You won't be able to find a spot where a detector never clicks. Ignoring that and putting the wires in the usual place would be equivalent to measuring the photon in the "left slit + right slit vs left slit - right slit" basis (or something of that nature), downgrading the entanglement between the two photons into correlation.
 
  • #3
Thank you for your response! If I understand correctly, the momentum entanglement would be destroyed. I'm not sure about path entanglement of whether it even makes sense to ask about that. However, would polarization entanglement remain intact? It seems like it should.
 

Related to How Would Afshar's Experiment Affect Entanglement?

1. What is Afshar's experiment?

Afshar's experiment is a quantum optics experiment designed to test the principle of complementarity in quantum mechanics. It involves passing a beam of light through a double-slit apparatus and then using a lens to focus the light onto a screen. By placing a wire grid at the focal point, Afshar was able to demonstrate that interference fringes can still be observed, even when information about which slit the photons passed through is available.

2. How does Afshar's experiment challenge the principle of complementarity?

The principle of complementarity states that certain properties of a quantum system, such as position and momentum, cannot be measured simultaneously with precision. However, Afshar's experiment shows that it is possible to obtain information about both the position and momentum of a photon simultaneously, which challenges this principle.

3. What is the significance of Afshar's experiment for entanglement?

Afshar's experiment has implications for the concept of entanglement in quantum mechanics. It suggests that entanglement may not be as fundamental to the theory as previously thought, as it is possible to obtain information about both the position and momentum of a photon without destroying its entangled state.

4. How does Afshar's experiment affect our understanding of quantum mechanics?

Afshar's experiment raises questions about the fundamental principles of quantum mechanics and how they apply to our understanding of the physical world. It challenges our current understanding of complementarity and entanglement and may require us to rethink our theories and models of quantum mechanics.

5. What further research is needed to fully understand the implications of Afshar's experiment?

Further research is needed to replicate and verify Afshar's results and to explore the implications of his experiment for our understanding of quantum mechanics. This may involve conducting similar experiments with different setups and varying parameters, as well as theoretical work to reconcile Afshar's results with existing theories of quantum mechanics.

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