Coincidence and Single Rate detection in Quantum Eraser experiments

[moving_on]

I am having difficulty understanding why the single rate of detection
(as opposed to the coincidence rate) is unaffected during Quantum Eraser experiments.
I'm looking at the great Kwait, Steinberg and Chiao paper:
'Observation of a "quantum eraser": A revival of coherence in a two-photon
interference experiment' Phys. Rev. A V. 45, No. 11 1/6/1992.
Say, for example, p. 7731:
'This demonstrates the coincidence dip at zero path-length difference to the beam
splitter. Note that the singles rate at either detector, given by ..., does not show
this dependence on path-length difference'.
I should probably try harder to get hold of the earlier papers quoted but I fear
I would need a less technical description anyway.
Probably a dumb thing to say, but a 'rate' is obviously the number of detections over
a set period of time. Surely one would expect a difference in such a 'rate' when there
is a greater likelihood of both photons going to one detector than when there is a
greater likelihood of both photons going to different detectors?
Or am I just being really, really stupid...

 

[azntoon]

The single rate of detection is unaffected in a quantum eraser experiment because the presence or absence of which-path information does not change the probability of detecting one photon. The two-photon interference pattern that is observed is due to the wave nature of the photons, meaning that the probability of detecting a single photon is the same regardless of whether you know which path it took or not. The coincidence rate, however, depends on the presence or absence of which-path information, since knowing which path each photon took allows you to determine if they were detected at the same time or not. This is why the coincidence rate changes when the which-path information is available.

 

[denian]

I can understand your confusion and difficulty in understanding the concept of coincidence and single rate detection in quantum eraser experiments. Let me try to explain it in simpler terms.

In quantum mechanics, particles such as photons can behave as both waves and particles. This means that a single photon can interfere with itself, creating a wave-like pattern of interference. In quantum eraser experiments, two photons are entangled, meaning that their states are correlated and dependent on each other. When these entangled photons are sent through a beam splitter, they can either behave as particles and go to separate detectors, or behave as waves and interfere with each other.

Now, in terms of coincidence and single rate detection, the coincidence rate refers to the number of times both photons are detected at the same detector. This rate is affected by the interference pattern created by the entangled photons. On the other hand, the single rate refers to the number of times only one photon is detected at a detector. This rate is not affected by the interference pattern, as the single photon can only be detected at one detector.

In the paper you mentioned, the authors are showing that the coincidence rate exhibits a dip at zero path-length difference, indicating interference between the entangled photons. However, the single rate remains constant because it is not affected by the interference pattern.

To address your question about the likelihood of both photons going to one detector vs. different detectors, it is important to note that in quantum eraser experiments, the photons are entangled and their behavior is correlated. This means that the likelihood of both photons going to one detector or different detectors is not dependent on the interference pattern, but rather on the experimental setup and the properties of the entangled photons.

I hope this helps clarify the concept of coincidence and single rate detection in quantum eraser experiments. It is not a dumb question to ask, as quantum mechanics can be quite counterintuitive. Keep asking questions and seeking understanding, as that is the essence of science.