- #1

Erik Ayer

- 75

- 4

- TL;DR Summary
- There is a tradeoff between coherence and entanglement which makes it necessary to use coincidence detection to observe interference of lack of interference. How does this work in...

As I understand it, either coherence or entanglement can be in an experiment or some of each, varying continuously between the two. Because of this, coincidence detection is needed to pick out interference patterns among all the data. Coherence would refer to quantum waves of photons taking different path not having a consistent phase relationship, as I understand it, so sending one of a pair of photons through a double-slit would mean they aren't in phase at the slits, and therefore the interference pattern would shift for each photon.

If that's the case, how is one specific pattern filtered out via coincidence? It would seem like the photons that are not going through the double slit would need to be separated somehow according to phase shift. How is this done for the quantum eraser? Here's the wikipedia diagram:

The upper beam is going directly to a detector. There is the 0.3mm mask in front of it, as well as a 1nm filter. Does that thin slit somehow correlate to a specific interference pattern on the lower part? I can't see how that would happen.

Looking at Birgit Dopfer's experiment:

Again the lower beam goes through a double slit, but in this case the entanglement in through momentum. Depending on the position of D_2, the momentum, and hence which slit an entangled partner went through, can be preserved or lost. Without coincidence there is no interference, and I think this is because the photons are not coherent and there are infinite overlapping interference patterns that add up to a Gaussian distribution. Assuming that D2 is at f such that which-way information is lost.

If that's the case, how is one specific pattern filtered out via coincidence? It would seem like the photons that are not going through the double slit would need to be separated somehow according to phase shift. How is this done for the quantum eraser? Here's the wikipedia diagram:

The upper beam is going directly to a detector. There is the 0.3mm mask in front of it, as well as a 1nm filter. Does that thin slit somehow correlate to a specific interference pattern on the lower part? I can't see how that would happen.

Looking at Birgit Dopfer's experiment:

Again the lower beam goes through a double slit, but in this case the entanglement in through momentum. Depending on the position of D_2, the momentum, and hence which slit an entangled partner went through, can be preserved or lost. Without coincidence there is no interference, and I think this is because the photons are not coherent and there are infinite overlapping interference patterns that add up to a Gaussian distribution. Assuming that D2 is at f such that which-way information is lost.