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PostPosted: Mon Feb 27, 2012 9:08 pm 
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Here is one of them...in case you are curious

"General &Science Wesley R. Elsberry on 22 May 2007 06:59 am
SciAm’s “Quantum Eraser” Home Experiment
Rachel Hillmer and Paul Kwiat have an article in the May 2007 Scientific American called “A Do-It-Yourself Quantum Eraser” (starts on p.90). This is a variant on one of the classic quantum mechanical experiments, the two-slit experiment. That’s the one where in trying to determine whether light has a wave or a particle nature, one comes to the answer that it has both.

Hillmer and Kwiat’s home experiment requires a laser pointer, a staple or paper clip, some metal foil, some stands to hold the laser pointer and other bits in place, and polarizing film ($7 on special from one source). And, of course, a room that is as dark as you can manage.

A pinhole in foil is used to restrict the laser pointer’s output. A rubber band or piece of tape can be used to keep the laser pointer on during the experiment. A straightened-out staple or paper clip (“the thinner the better”) is placed in front of the laser pointer such that it is in the middle of the beam. (Depending on the make of your laser pointer, you may need to use a piece of the polarizing film just in front of it to obtain a polarized beam. See the instructions in the article.) In the dark and beyond that, one should see an interference pattern on a wall or piece of paper. That’s a series of vertical bars, and it indicates that the laser beam is acting as a wave as it passes around the metal obstacle.

H&K discuss the construction of what they call a “path labeler” from two pieces of polarizing film abutted such that their planes of polarization are perpendicular to each other. The metal obstacle goes exactly at the join between those pieces. This means that laser light going around one side of the metal will be polarized in one direction, and going around the other side it will be polarized at a 90 degree angle to that. The effect should be that there are no longer the bars of the interference pattern seen at the screen. In this setup, one can learn about which path a particular photon took, and the laser beam acts as a stream of individual particles.

Up until now, this has all been essentially replicating the two-slit experiment, but in your home. Now comes the “quantum eraser” part. Take another piece of polarizing film and put it in the light path after the metal obstacle and path labeler, where its plane of polarization is at a 45 degree angle to one of the parts of the path labeler, let’s say by turning it clockwise. The interference pattern will again be seen. This is described as the result of the path becoming indeterminate again since the polarization cue to which path a photon took no longer exists. The polarizer has acted as a “quantum eraser” of information. There is also a description of an “antidiagonal” quantum eraser, made by using a piece of polarizing film rotated 45 degrees counterclockwise. One can construct a piece that applies both “erasers” at once, yielding an interference pattern that display bars and gaps at the top and bottom, where a bar on the top is matched with a gap on the bottom.

This experimental setup got my attention. It is simple, cheap, portable, and produces clear results that bring quantum weirdness right into your living room. The author biographical information with the article reveals that Rachel Hillmer is an undergraduate student at the University of Illinois, and Paul Kwiat is Bardeen Chair of Physics there. My hat’s off to both of them.

Addition: Consider the effect of adding a pellicle or beam-splitter following the metal obstacle/path labeler but before the quantum ereaser. I need to set this up to try out; a simple beam-splitter could be just a piece of flat optical glass, like a microscope slide."

And this discussion

http://www.physicsforums.com/showthread.php?t=399029

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PostPosted: Tue Feb 28, 2012 12:18 am 
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Off the top of my head: No, I do not think that this is a good QM experiment. It confuses too many issues. first exp: The one thing it does do is what I said was easy -- creating a diffraction pattern. Second Exp: The diffraction goes away because the beams are orthogonally polarized not because of any quantum decoherrence. Third exp: When the 45 degree polirizer is placed in one path one is likely to get half the light forming a diffraction pattern and half piling up behind the slits. This is purely an optics experiment, not a quantum experiment. It demonstrates what polarizers do to light and no QM is needed to explain what happens.

Tom


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PostPosted: Thu May 19, 2016 11:29 am 
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I know this is a very old post, but I noticed that Tom seems to be misrepresenting something here. Perhaps he's changed his opinion as it has been a while.
twcjr wrote:There are certain points on this imaginary detector D0 that can only be hit if a probability wave creates a diffraction pattern and others that can only be hit if a particle goes through one slit or the other -- and these points do not overlap. If you measure exactly where a photon hits D0 the instant it hits and it happens to hit in the areas where the diffraction pattern hits would go, then the idler photon must register in either D1 or D2. If it happens to hit in the areas where the two lumps behind each slit would go, then the idler photon must register in either D3 if it fell in the bottom lump zone or D4 if it fell in the top lump zone. When one looks at the data location on D0, one brings information into PMR that defines the path that the idler photon must take: top slit, bottom slit, or neither/both. Consistency requires this result. The violation of objective causality works in either direction. One way, the results of D0 are forced to verify the information collected by D1-4 even though the D0 data collection preceded the D1-4 collection. The other way, the photons choice to reflect-or-transmit at the beamsplitters are forced to verify the data collected by D0 even though that data is collected before the choice is made. In both cases, the probabilities in the probable future database are configured by TBC to maintain consistency within the VR.
I'm not sure how Tom is arriving at these conclusions. Measurement ad D0 can never tell us which detector its entangled partner should go to. The reason for this is in the experiments results, which are in the attached picture. What we always get at the end of the experiment is what you see at D0. Notice that the resulting patterns at R1-R4, when combined, equal the pattern at D0. This means that while it is true that there are only certain places particle X can hit at D0 if its partner went to D1, we can't know what those places are until after the experiment is done and we sort through the data. Basically, pick any particle at D0 and its partner could have gone to any detector.

Tom: your statement: "... TBC has to make a choice for D1-4 to fit future data sorting." is correct if what you mean by that is what I described above. The latter (attributed to kroeran) is not correct. The measurement of where the particle hits D0 produces the “whichway” information.

Tom
Measurement at D0 does not create "which path" information. Because all of the patterns created at D1-D4 add up to the pattern displayed at D0, if you pick any one particle out at D0 you cannot determine from that info alone where its partner landed. Try it yourself with the attached picture. Pick any point within the red at D0 and call that a particle. Do you know now which detector its partner went to? No...it's not possible. It could have gone to R1-R4. That information(as to where particle X hit in relation to its entangled partners path) is only available retroactively at the end of the experiment once you plot the data and look at the time stamps of when each entangled pair was produced and where they landed.


Attachments:
Detector0RawResults_svg.png
Detector0RawResults_svg.png [ 14.53 KiB | Viewed 3988 times ]

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PostPosted: Thu May 19, 2016 3:07 pm 
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The key to understanding what I wrote is the word "imaginary" in the first sentence: "There are certain points on this imaginary detector D0 that can only be hit... " The "this" in ["...this imaginary detector..."] is referring to other text that has been omitted. So the context for my comment has been lost. If you had that context I think you would find that I am talking about a hypothetical version of this experiment where the detectors can produce and record) an x coordinate of exactly where each individual particle hits. And where the experimental parameters (wavelength, slit separation, etc) have been modified to spatially separate the diffraction pattern from the clump pattern as much as possible.

Indeed, in the experiments I am planning to discuss in the near future (trying to encourage physicists to perform these experiments), I have specified a remake of the delayed erasure experiment where data collected at D0 can accurately predict which path the entangled idler particle will take. A detailed explanation will be available when the experiments are edited and released on YouTube.

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PostPosted: Thu May 19, 2016 6:50 pm 
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I see. Your conclusions here(and elsewhere, heh) differ greatly from what is accepted as possible by science currently. I was just unclear as to how you got there. I am not you, so all I can imagine is how the experiments we have now already work rather than how they could be altered to create a new result. Interesting that future prediction is thought impossible, but it may just be that our experimental setups are wrong.

I see that some have made attempts to do this by somehow trying to send information from "alice" to "bob" through space faster than light. But they don't know that information is nonphysical, now do they?

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PostPosted: Wed Jun 01, 2016 7:12 am 
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Have you guys noticed that there is a new push amongst physicists to resurrect the Bohm pilot-wave theory, which postulates that the electrons are guided by a wave in some sort of aether. This is an attempt to do away with the Copenhagen Interpretation and return to physical determinism:

http://revolution-green.com/bit-quantum-weirdness/

Oddly, they seem to be getting some good results in their tests. We'll see.


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PostPosted: Thu Jun 02, 2016 7:14 am 
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vzam wrote:Have you guys noticed that there is a new push amongst physicists to resurrect the Bohm pilot-wave theory, which postulates that the electrons are guided by a wave in some sort of aether. This is an attempt to do away with the Copenhagen Interpretation and return to physical determinism:

http://revolution-green.com/bit-quantum-weirdness/

Oddly, they seem to be getting some good results in their tests. We'll see.
There are so many things wrong in that article I don't know where to begin. First, there is no such thing as a copenhagen interpretation. It was called the copenhagen statement at inception, only later relegated to an 'interpretation' after materialist scientists invented many worlds and other real 'interpretations'. You can't have a 'statement' and an 'interpretation' both existing at the same time and both being possibly right. So the 'statement' became just another interpretation.

The copenhagen statement does not say that a particle is a probability distribution before measurement and travels through both slits before interfering with itself and creating a diffraction pattern. That is an interpretation. The statement is nothing more than face value, empirical data that describes what the experiment seems to be telling us. It states that particles sent through an experiment one at a time can only be described mathematically as a quantum probability distribution until they are measured, after which time they can be described classically as a particle with a definite trajectory. The fallacious arguments and criticisms against the copenhagen statement only arise when people try to interpret the 'probability wave' as something that exists or is real. It's not.

This has been emulated using bouncing oil-drops on an oil-bath, so can be visualised and tested.
I'm sure he means "water" bath, as oil floats on water. We can also emulate a quantum diffraction pattern with water waves...no oil drop needed. The problem is not whether we can emulate how we THINK the particle is behaving before it's measured. The problem is, how does it 'transform' from a wave to a particle or vice versa. If you touch a water wave it doesn't turn into a particle in any experiment.

In the Copenhagen interpretation, the single electron magically passes through both slits and interferes with itself and has no defined path,
Here he uses hyperbole to try and back up a point that is not based in reality. Because he cannot understand how or why the 'copenhagen interpretation' should work the way it does, he calls it magic. He replaces it with this:

but in the Bohm interpretation this splitting of a single particle does not happen.
Which makes much more sense to a mind that believes every particle in the universe must be existing in a definite position at all times. He hasn't fit the theory to the data, he's fit the data to his theory. Not good. This is not even bad science. It's not science at all. It's making up stories that conform and make sense to a certain worldview.


Of course, in the Bohm idea we now have a wave that is vibrating in *something* so we’re explaining something by adding in something we can’t yet explain
Which is exactly the same problem the entirety of science has now. Copenhagen statement doesn't make sense? Let's add a particle and have it 'riding' a probability wave instead of just a probability wave by itself. Where does that pilot wave come from and why does it collapse? Who knows...but at least we have a PARTICLE now! Where does mass come from? The higgs boson! Where does that come from? The higgs field (which doesn't exist). Where does the higgs field come from? Who knows, but at least we know there is a particle that gives other particles mass! What gives that particle mass? Can't explain that, can we.

The truth is, pilot-wave theory explains nothing. Its purpose is none other than to fit the data to a pre-existing view of how the world "should" work. The only thing it does is move the problem of wave collapse up one level.
I haven’t spent a lot of time on this so far, but that McCulloch can explain the reason that galaxies don’t fly apart without needing to invent dark matter is a major point in favour.
He talks about dark matter being invented, but fails to realize that pilot-wave theory is an invention of equal proportions.

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