No, they’re essentially the detectors giving the which-path information, and thus essential for the effect. If two photons are in an entangled state, detecting the polarization of one gives you instantly information about the polarization of the other. Thus, by detecting the polarization of the signal in the experiment, you know the polarization of the idler, and thus, which quarter wave plate it traversed, and hence, which slit it went through. They’re basically the detectors D[sub]3[/sub] and D[sub]4[/sub] in the wiki version of the experiment.
Yes, I think I covered that in my explanation in the OP. But how are the probabilities affected?
If you can access the which-path info, they’re additive; if you can’t, they’re not. That’s what this whole thing is about…?
So is this a fair summary?
Take the entire system, across time and space, and any measurement (or ability to access which-path info) at any point in time/space, immediately constrains the possible states of the system over the entire scope of time and space.
Yes, but one must be careful here: it’s not the case that with the later choice of whether or not to extract the which-path info, one actually influences the physical processes at the earlier time. If it worked like that, you could send messages backwards in time, simply by deciding in the future whether or not an interference pattern is measureable at any given time in the past.
I’m sorry but you’re wrong. There is no way to influence the choice on the p path since the choice on the s path is DESIGNED to be dependent on the p path choice and that is not made until AFTER the s path measurement has been made - that is in the second iteration of the experiment.
There are 2 iterations. Each iteration is in 2 parts.
I’m sorry but what?
Oh come on. Exactly how am I supposed to respond to that? :rolleyes:
Tell me what exactly about my statement you disagree with, and why you think it’s wrong. As it stands, I just can’t figure out what your post was supposed to tell me.
Sorry, but I don’t see how I can be any clearer.
OK, so I guess you don’t have anything to say after all.
If you looked at the experiment, what I posted is perfectly plain. How it argues against the idea that the results are a simple matter of probabilities or preselection will be equally clear. So if it doesn’t make any sense to you, then that would cause me to strongly suspect that you have not reviewed the data.
Well, perhaps, in order to try and get something useful out of this conversation after all, at least for anybody else who might read this, let me at least be as clear as possible about what I mean. It’s slightly easier to take the wiki version of the experiment for this, but the two are completely equivalent in all essential ways.
So in the wiki version, there are five detectors: one, D[sub]0[/sub], registers the signal photon, and the others, cleverly named D[sub]1[/sub] to D[sub]4[/sub], register the idler. Detectors 3 and 4 record which-path information; detectors 1 and 2 don’t. The measurement is done via a coincidence counter: it registers a count if both D[sub]0[/sub] and any of D[sub]1[/sub] to D[sub]4[/sub] click. The interference pattern then is created if one looks at the instances where both D[sub]0[/sub] and D[sub]1[/sub] or D[sub]2[/sub] registered a photon; if one looks at the instances when D[sub]3[/sub] or D[sub]4[/sub] fired together with D[sub]0[/sub], no interference pattern is observed.
But this is the crucial thing: the detections of the different detectors must be brought into coincidence in order to observe the interference pattern. If only the counts at the detector D[sub]0[/sub] were analyzed, no interference pattern would be observed, ever. This is the reason you can’t send a signal into the past. That is, the physical pattern of photons incident on D[sub]0[/sub] does not change due to the choice made later on; the knowledge of the which-path info merely changes the probability distribution used to describe the detections.
Clearly you haven’t even looked at the link in the OP. They aren’t even remotely the same so until I have some indication that you actually know what you’re talking about I won’t be responding to you.
A couple points:
1 - Half Man Half Wit, in my experience, is not only very knowledgeable, he is one of the most polite and unbiased posters on this website. I think you might want to give him a little more credit than you seem to be.
2 - Both your link and the wiki have basically the same title of delayed choice quantum erasure (if you get to the bottom of yours where they get to the delayed part). I’m not a physicist but they sure sound about the same.
Thanks RP. But the difference is so clear that all that is really necessary is a cursory glance at the equipment diagram for each experiment. The one in the wiki is easy to find. There are several in my link, but this is the one that is most relevant.
There are 5 detectors in the wiki, 2 in the OP. 2 prisms, vs no prisms, no polarizing filters vs 1 filter and 2 quarter wave filters, entangled photons are generated after the double slit vs before . .
I mean, they’re so different it’s hard to actually come up with a catlog of differences.
I believe the only difference is the specific mechanisms used. One is using polarization to gain information on the back end, and the other is using beam splitters and then the constructive or destructive interference of those beams.
The beam splitters alone make it fundamentally different. The 50-50 probability they introduce is not quantum mechanical. A beam splitter will always reflect 50% of the the photons and pass the rest.
Also, no modifications are ever made to either photon, unlike in the OP.
Have you read the experiment in the OP? I really don’t understand why this seems to be such a chore for every one. If/when you do, you won’t feel the need to ask such questions.
In the OP the polarization changes, in the wiki the phase changes depending on whether it was reflected or passed through, right? I only skimmed the wiki.
Yes, I read the article in the OP, and then I skimmed the wiki before I wrote that post. In one case polarization is used to detect path and in the other case phase, at least that what it seemed like.
Am I reading the wiki wrong when I say they used phase in the same way the other one used polarization?
The OP is more complicated since operations performed on one photon are used to manipulate the other. Also in the OP there are at least 3 different types of modifications to the polarization.
I don’t mean to be rude, but I don’t see the point in spending my time trying to distinguish these experiments. If anyone wants to claim that simply because they have the same name that ergo, they’re identical, that’s fine. I don’t really see why that should oblige me to invest my time in demonstrating otherwise, especially when it is such a trivial matter to simply read the 2 or 3 pages at the original link.
But if there are others who wish to use this thread to join you in this discussion, I have no objection. Enjoy!