Delayed choice quantum eraser experiment

[honzik]

Hi,
I would like to ask some questions regarding "delayed choice quantum eraser experiment". (I think it is possible for those who are familiar with this experiment to skip the text and go ahead into questions 1 and 2.) It is mentioned e.g. on these links:
http://strangepaths.com/the-quantum-eraser-experiment/2007/03/20/en/
http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser
Let's talk about picture depicted in http://strangepaths.com/wp-content/uploads/2007/03/qe.png (from the first link). To briefly describe the experiment:
There are two slits A and B from which (from A or B) two entangled photons are emitted. One goes into detector D0 and the other (its counterpart) goes into one of the detectors D1, D2, D3, or D4. If it comes into the D3 or D4 detector, we can deduce what slit (A or B) it came from - on the other hand when it comes into D1 or D2, we cannot.
Now comes interesting part: photons detected on D0 don't exhibit any interference pattern when watching them altogether (ie. for their counterparts detected on D1, D2, D3 and D4 altogether). The same is true when watching only photons detected on D0 whose counterparts were detected only on D3 (or only on D4). But when watching photons detected on D0 whose counterparts were detected only on D1 (or only on D2) we see interference pattern on D0.
But the most interesting thing is that the above is true even if the distance between A(or B) and D0 is smaller than distance between A(or B) and D1(D2, D3 or D4) - and even smaller than distance between A(or B) and BSA(or BSB) - see picture mentioned above. Suppose for the next text that this distance assumption is true.
These are the facts (or am I wrong?) But it seems it's really strange. My questions are:

1) Is the same as above (especially presence of interference pattern) true when we will send photons less frequently so that the next one will be send after the previous hits one of the D1,D2,D3,D4 detectors (and of course its counterpart hits D0)?

2) (Key question of this topic) What if (in case point 1 is true) the beam splitter BS (see picture mentioned above) is present at the beginning of emiting one photon though A or B slit and will be removed just after the photon has reached D0 detector (ie. before its counterpart hits BS - or even before its counterpart hits BSA(BSB) but the latter is not so important). Will we also notice the interference pattern on D0 detector only for those photons whose counterparts have reached only detector D1 (or only D2)? (Before emisson of the next photon, the beam splitter BS will be installed on its original place again and so on...)


Thank you very much for answering. I hope I have explained my questions clearly.

Honzik

 

[DrChinese]

1) Is the same as above (especially presence of interference pattern) true when we will send photons less frequently so that the next one will be send after the previous hits one of the D1,D2,D3,D4 detectors (and of course its counterpart hits D0)?

2) (Key question of this topic) What if (in case point 1 is true) the beam splitter BS (see picture mentioned above) is present at the beginning of emiting one photon though A or B slit and will be removed just after the photon has reached D0 detector (ie. before its counterpart hits BS - or even before its counterpart hits BSA(BSB) but the latter is not so important). Will we also notice the interference pattern on D0 detector only for those photons whose counterparts have reached only detector D1 (or only D2)? (Before emisson of the next photon, the beam splitter BS will be installed on its original place again and so on...)

1. You can slow down the rate of photons, and you will still see the interference. PDC photons are produced relatively sporadically anyway - on an order of hundreds per second depending on the setup.

2. If you remove the BS as the photon flies by so, then you will know the which-path information completely. No interference will be seen once you correlate. That is true even if the detection event at D0 has already occurred.

 

[Entropia]

,

Thank you for your interest in the delayed choice quantum eraser experiment. This experiment is indeed quite fascinating and has sparked many discussions and debates among scientists. To answer your questions, I will first provide a brief overview of the experiment and its implications.

The delayed choice quantum eraser experiment is a variation of the double-slit experiment, which is a fundamental experiment in quantum mechanics that demonstrates the wave-particle duality of matter. In this experiment, a beam of particles (such as photons) is directed towards a barrier with two slits. On the other side of the barrier, a screen is placed to capture the pattern of the particles after they pass through the slits. When the particles are observed, they behave like particles and create two distinct bands on the screen. However, when the particles are not observed, they exhibit wave-like behavior and create an interference pattern on the screen.

Now, in the delayed choice quantum eraser experiment, the particles are sent through the barrier one at a time and their behavior is observed. However, the interesting twist is that the experimenter can choose to observe or not observe the particles after they have passed through the barrier but before they reach the screen. In addition, the experiment also involves entangled particles, which means that the behavior of one particle is dependent on the behavior of its entangled counterpart.

Now, to answer your questions:

1) The presence of the interference pattern is dependent on the observation of the particles. If the particles are not observed, they will exhibit wave-like behavior and create an interference pattern on the screen. So, in the case of sending the particles less frequently, the interference pattern will still be present as long as the particles are not observed.

2) The key question here is whether the beam splitter affects the behavior of the particles after they have passed through the barrier and before they reach the screen. Based on the principles of quantum mechanics, the answer is no. The particles have already passed through the barrier and their behavior has been determined before the beam splitter is removed. Therefore, the interference pattern will still be present on the screen for the particles that are not observed, regardless of whether the beam splitter is present or not.

I hope this answers your questions and clarifies any confusion. The delayed choice quantum eraser experiment is still a topic of ongoing research and discussion, so there may be different interpretations and explanations for its results. Thank you again for your interest and curiosity about this fascinating experiment.