DrChinese said:I think the context of the entire experiment is relevant. Not just the "first" detection. How you interpret the results is dependent on that context, and that will not be known until later - when all of the results can be brought together into a single place. And then it will in fact appear "as if" the past was dependent on the future.
You can interpret this in different ways. And there are other delayed choice experiments which evidence the same thing. Consider Zeilinger et al:
http://arxiv.org/abs/quant-ph/0201134
From middle of page 5:
"Such a delayed-choice experiment was performed by including two 10 m optical fiber
delays for both outputs of the BSA. In this case photons 1 and 2 hit the detectors delayed
by about 50 ns. As shown in Fig. 3, the observed fidelity of the entanglement of photon 0 and
photon 3 matches the fidelity in the non-delayed case within experimental errors. Therefore,
this result indicate that the time ordering of the detection events has no influence on the
results..."
sanpkl said:interesting...it will take me a few days to understand the paper...thanks for the link and your post
cthugha do you want to take a stab at this and summarize it...?
sanpkl said:ok. now let's say we detected the signal photon position and its at (x, y) = (1.5, 120) and it lies on figure 3.
actually y does not matter..its just a count (that can be converted to probability).
so, let's assume, we are reasonably sure (after pattern formed by gazillion photons prior) that signal photon position lies on figure 3.
sanpkl said:1. if we choose which way info...are we likely to detect idler at D1?
sanpkl said:2. if we do not chose which way info...are we likely to detect idler at?
sanpkl said:2b) the signal is on fig 3, suggesting interference and no which way..however if we make which way experiment on idler...then won't signal be saying interference and idler which way?
sanpkl said:Please give example of kind and amount of information one can gain (about idler?) from knowing the position of where signal was detected. this will help me understand better.
sanpkl said:interesting...it will take me a few days to understand the paper...thanks for the link and your post
cthugha do you want to take a stab at this and summarize it...?
Cthugha said:Ok, so we have a detection at x=1.5 and have recorded the coincidence patterns for a while, right?
correct.
does this mean the signal photon has a higher probablity of being on figure 3? when its is later correlated with idle
can the probablities of idler striking d1, d2, d3, d4 be, now, calculated
given that: signal was detected at x=1.5?
if you choose to destroy which-way info, you are likely to detect the idler at D1. If you keep which-way info you will see a detection at D3 or D4 with equal probability.
if we leave the "choice" (of "which way" or not) upto the idler photon..(as in the kim scully experiment)...is it likely to be detected at D1 ...instead of d2, d3, d4?
given the context above...i.e. ...signal photon was detected at x = 1.5 mm
sanpkl said:if we leave the "choice" (of "which way" or not) upto the idler photon ...is it likely to be detected at D1 ...instead of d2, d3, d4?
given the context above...i.e. ...signal photon was detected at x = 1.5 mm
maybe its possible to calc the probalitities?
Cthugha said:sanpkl said:Yes, that is possible. Whether a photon goes to D1/D2 or D3/D4 depends on the splitting ratio of the beamsplitters BSA and BSB (see the setup in the Kim paper). Assuming they are 50/50 beamsplitters, 25% of all photons will go to D3 and another 25% will go to D4. The remaining 50% will go to either D1 or D2. How many of these 50% go to D1 and how many go to D2 can be extracted from figures 3 and 4. Having a look at position x=1.5 again, you see that there are roughly 120 coincidence counts for D1 (fig. 3) and roughly 40 coincidence counts for D2 (fig. 4). so for that portion of the total counts you have a distribution of 75% D1 and 25% D2.
So in total you get:
D1: 75% of 50% =37.5%
D2: 25% of 50% =12.5%
D3: 25%
D4: 25%
Cthugha,
at x= 1.5mm ,
figure 3 = 120, fig 4 = 40
why are fig 5 and fig 6 (not shown) not 80 each?
given that the paper says this is 50/50 beam splitter...
Answer: not all idler photons were able to be collected...fig 3 and 4 are comparable to each other but not comparable with fig 5 and 6
why would figure 6 have a small shift of center relative to figure 5? are the path lengths not same?
sanpkl said:why are fig 5 and fig 6 (not shown) not 80 each?
given that the paper says this is 50/50 beam splitter...
sanpkl said:why would figure 6 have a small shift of center relative to figure 5? are the path lengths not same?
Cthugha said:Yes, that is possible. Whether a photon goes to D1/D2 or D3/D4 depends on the splitting ratio of the beamsplitters BSA and BSB (see the setup in the Kim paper). Assuming they are 50/50 beamsplitters, 25% of all photons will go to D3 and another 25% will go to D4. The remaining 50% will go to either D1 or D2. How many of these 50% go to D1 and how many go to D2 can be extracted from figures 3 and 4. Having a look at position x=1.5 again, you see that there are roughly 120 coincidence counts for D1 (fig. 3) and roughly 40 coincidence counts for D2 (fig. 4). so for that portion of the total counts you have a distribution of 75% D1 and 25% D2.
So in total you get:
D1: 75% of 50% =37.5%
D2: 25% of 50% =12.5%
D3: 25%
D4: 25%
sanpkl said:Continuing with the above experiment...for the millionth plus one signal and idler..where signal photon has been detected at D1..
sanpkl said:Case 1: now if we change the beam splitters to 100/0 (where 100 is no which way), what are the probablities?
D1= 0, D2 = 0, D3 = 50, D4 = 50?
sanpkl said:Case 2: we add a quantum eraser (the polarizer kind) in the path of idler where we change to no which way. what are the probablities?
D1= 0, D2 = 0, D3 = 50, D4 = 50?
Would adding a quantum eraser (in which we control the choice), say of the polarized kind, in the kim scully experiment work?
Cthugha said:Do you mean D0?
Do you mean that 100/0 is complete which-way information (No which-way means you get the interference pattern, complete which-way info means no interference pattern)? Then your reasoning is correct.
In principle you can add a polarizer kind quantum eraser. The results will then of course depend on your choice of settings.
DrChinese said:I think the context of the entire experiment is relevant. Not just the "first" detection. How you interpret the results is dependent on that context, and that will not be known until later - when all of the results can be brought together into a single place. And then it will in fact appear "as if" the past was dependent on the future.
..."
sanpkl said:cthugha, eagle,
all of the below might have been answered before but i just wanted to go over it again...with a different rephrasing...
with reference to the delayed choice quantum eraser...http://arxiv.org/abs/quant-ph/9903047
1 a) when a signal photon has been detected on Do, has not the pattern of signal photon (Though *unknown* to us, till we compare with idler in coincidence counter) already been fixed/sealed? does that mean same as "experiment is over"?
i understand that a single photon not a pattern make, i am referring to the direction/potential
1. b) once the signal photon is measured is the fate/path of the idler also "somewhat" sealed (with a high probability)?
this would resolve/invalidate the "past can be changed" hypothesis/misunderstanding, i guess
2. once the signal photon is measured, we till don't know which figure 3,4,5,6 would it fall, until we compare with idler?
this would resolve/invalidate the "faster than light information travel" hypothesis/misunderstanding, i guess
3. the position of the signal photon on Do has nothing to do with what is what we are doing to the idler at that point in time (i.e. at the exact time the signal strikes Do). if i remember correctly cthugha said similar.
this would help resolve/invalidate the "past can be changed" hypothesis/misunderstanding, i guess
cthugha wrote
<In the DCQE experiments the measurement is different. You gain phase information. And once you do so on the side of D0 you get a well defined phase and can therefore predict what will happen on the other side - as phase is the property which determines what happens in a Mach-Zehnder interferometer. However in most cases this will be a probabilistic prediction like "with 70% probability that photon will go to D1">
for me the "70% (or higher than 50%) probablity" explains a lot...
4. i guess that this would also help reduce the need for "many worlds" hypothesis
5. wave function collapses (for both twins-- idler and signal) when either the signal or idler photon is detected?
eaglelake said:My response was to the original post which referred to a single photon experiment. Your questions now concern an entangled two-photon experiment. The paper you cite is not an easy read. (At least I did not find it so.) There is a more understandable, non-mathematical, discussion in Walborn et al, arXiv:quant-ph/0503073v1 and also in Roussel and Stefan, arXiv:0706.2596v1. I hope this helps.
Best wishes
”Bob, that is amazing! You have control
over the past! While you are at it, can you go back
change my lottery ticket from last week to 67-81-138?,”
Alice asks with a look of awe in her eyes. Bob is loving
the moment, but he is not the greatest magician, and
cannot keep his mouth shut about the secret to his tricks.
”No Alice, look, the photons I gave you were actually entangled
with photons that I kept for myself. I did a series
of polarization measurements, and recorded my results.
My polarization measurements tell me how to divide up
your experimental results so that we can see interference
or not, but I cannot change the position at which any
photon actually landed,” Bob explains. He shows her by
plotting all of the results for which he measured horizontal
OR vertical (orthogonal directions) and they observe
the large mountain peak. He then does the same with
all results of +45◦ and −45◦, and they observe the same
mountain peak. Of course plotting all of the results together
regardless of polarization also gives the mountain
peak, as Alice had already observed. So Bob was not able
to alter the past, it is just that he had more information
than Alice.
It
is wrong to speak of the ”route ” of the photon in the experiment of the beam splitter. It is wrong to
attribute a tangibility to the photon in all its travel from the point of entry to its last instant of flight.
sanpkl said:perhaps there is a "dimension" in addition to time-space, through which quantum mechanics operates? the "probability wave function" operates in that dimension.
when we try to measure a photon's position, the wave function collapses, the photon moves back into the time-space dimension