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Quantum entanglement actually can transmit information?


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Let me start with apologies. I can't find english version of this video. I'm sure we all would greatly appreciate if someone fluent in portuguese could provide even rough translation :)

In a nutshell: a group of Brasilian scientists made a cardboard cutout of a cat silhouette, then used laser and crystals to create entangled pairs of photons. Then they made a photo of a cat using half of the photons. The other photo was created by the second half of the photons - the one that never came in contact with the cardboard cat. Essentially, this is a "quantum echo picture".

Discuss?

Edited by Scotius
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Is there a peer reviewed paper published yet? That image would be easy to create in photoshop.

(And to save other readers the trouble, the whole video is a still shot of what you can see without playing it.)

Edited by HebaruSan
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It's Spanish not Portuguese!

The video description says (the speech in the video is just someone reading this text):

"Scientists manage to capture an image of Schrodinger's Cat

An international group of physicists have shown for the first time images taken with a camera without using a real object. Experts say that the idea can be useful in medicine.

In their experiment, the scientists from Viena and New York used a laser and a stencil of a cat. The scientists did not choose the stencil of the cat by chance (however it could have been any other object), But because this aludes to Schrodinger's paradox.

Shrodinger's paradox helps to explain the complexities of quantum mechanics. The Austrian physicist Erwin Schrodinger presented in 1935 an experiment about an imaginary cat trapped in a box, that could be both dead and alive at the same time, to demonstrate quantum entanglement of particles.

The experiment by Anton Zeilinger and Gabriela Barreto Lemos is based on the same idead and they were able to 'take photos of Shrodingers quantum cat' in the process, following an according to an article published in Nature.

The scientists made a circuit across which they shot pairs of yellow and red photons and with different wavelengths (after coming from a divided green photon). The yellow photons were sent toward the sillouette of the cat while the red photons toward the camera. By the phenomenon of quantum entanglement, the red photons formed an image of the cat thanks to their entanglement with their paired yellow photons.

The device with which the experiment was performed can be found in use in medical applications. According to the scientists, images of damaged tissues can be created. The investigators have filed a patent application."

 

I think using Schrodingers cat to describe this experiment is not right, but done to illustrate it to a general audience. And yes it is peer reviewed! There is a paper in Nature and here is some discussion http://www.nature.com/news/entangled-photons-make-a-picture-from-a-paradox-1.15781

and here is the paper http://www.nature.com/nature/journal/v512/n7515/full/nature13586.html

Edited by jf0
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2 hours ago, kurja said:

I could be completely wrong but afaik transferring information was always possible, just not doing so FTL.

I gave up the notion that information could not be transferred a couple of years ago. I don't even think FTL is a limitation for entanglement since for quantum states speed and time have much less meaning.

 

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9 minutes ago, PB666 said:

I gave up the notion that information could not be transferred a couple of years ago. I don't even think FTL is a limitation for entanglement since for quantum states speed and time have much less meaning.

 

Transmitting information FTL breaks causality. Remember the speed of light has nothing to do with light.

Edited by Majorjim
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This is an example of Quantum Teleportation, which uses entanglement to send information, but it's not using just entanglement. Basically, you can leverage entanglement to send along a lot more data than you would otherwise, or send very different data than you thought you were sending. But there still has to be a classical communication channel that obeys speed of light limits.

It is extremely exciting to see this done with actual packets of data, rather than individual particle states. Experiments like this bring us a step closer to real, practical teleportation. It may be one step out of millions, and I would absolutely not hold one's breath for having it in our life time, but exciting nonetheless.

1 hour ago, Majorjim said:

Transmitting information FTL breaks causality. Remember the speed of light has nothing to do with light.

Causality is also a softer subject in QM. There is still a notion of overall causality, but it's very different from what you normally picture in classical mechanics. Energy arriving at destination before leaving origin, for example, is totally kosher. Information arriving before it left, not so much. Not without CTCs, anyways. Which, of course, are a feature of underlying Field Theory. At any rate, I wouldn't put too much stock in Causality. It's a comfortable notion, but not one as strictly enforced in actual physics as some people seem to think.

Edited by K^2
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Just now, K^2 said:

This is an example of Quantum Teleportation, which uses entanglement to send information, but it's not using just entanglement. Basically, you can leverage entanglement to send along a lot more data than you would otherwise, or send very different data than you thought you were sending. But there still has to be a classical communication channel that obeys speed of light limits.

It is extremely exciting to see this done with actual packets of data, rather than individual particle states. Experiments like this bring us a step closer to real, practical teleportation. It may be one step out of millions, and I would absolutely not hold one's breath for having it in our life time, but exciting nonetheless.

Causality is also a softer subject in QM. There is still a notion of overall causality, but it's very different from what you normally picture in classical mechanics. Energy arriving at destination before leaving origin, for example, is totally kosher. Information arriving before it left, not so much. Not without CTCs, anyways. Which, of course, are a feature of underlying Field Theory. At any rate, I wouldn't put too much stock in Causality. It's a comfortable notion, but not one as strictly enforced in actual physics as some people seem to think.

Yes, yes all bets are off in QM. Classical causality must be taken into account still though.

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26 minutes ago, Majorjim said:

Yes, yes all bets are off in QM. Classical causality must be taken into account still though.

Which is fine, because communication via entanglement always relies on a classical channel of some sort, so if classical channels preserve causality, then QM channels preserve causality.

But if you happen to have a wormhole that causes a time loop, or something along these lines, classical channels no longer preserve causality, and classical physics runs crying back to QM to save the day. Whether or not QM actually saves the day when causality is violated depends on some of the aspects of underlying field theory. I really hope it does, though, because there are no real mechanisms to prevent CTCs, at least on a small scale, and that would mean we'd be in for bad times if causality does get violated somewhere in the universe. Which is a big place. So even if it's very, very hard to build a time loop, you know someone out there is going to manage it.

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1 hour ago, kmMango said:

Do we have any idea what would happen to an observer in a CTC, or at least some educated guesses?

Educated guesses, since experiments in this regard are rather limited. (You can "fake" a time loop in some optical setups with lasers, but it's not exactly the same.) Nonetheless, all of the theory that doesn't blow up seems to suggest that observer would encounter history that's only consistent so far as his own timeline is concerned. It's easiest to interpret via MWI, because you can think of contradictions as observer simply encountering different parallel timelines, but the gist is the same in Copenhagen.

In other words, no fading photographs, Marty McFly style. Instead, you'll just have a piece of documentation or memory from your other visit to the same period that doesn't match what's currently happening.

If you subscribe to Copenhagen interpretation, or any other interpretation involving collapse, from perspective of other observers, a traveler who steps out of a CTC wormhole might as well be a random quantum fluctuation. Astonishingly unlikely one, but that's the sort of stuff you get in your QM when you construct time loops. Honestly, time travel will ever only make complete sense to the traveler.

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i'm wondering - if we could slow down the light to really low speeds these entangled pairs of photons, would it break entanglement ?

(some managed to really slow down light to a crawl)

http://www.photonics.com/m/Article.aspx?AID=28520

Combined with the technique presented in this thread, you first create your entangled pair, then slow down both sets of entangled photons, move one set while it's still in it's slowing medium.

 

If entanglement is still preserved in this case, then wouldn't it be possible to :

- Place the image you went to send on one side (maybe something akin to a QR code if you want to send data)

then on the other side, wait until a predetermined time (as you should be able to determine in advance when the entangled pair of photons exits both slowing down medium) to record the result. 

 

Though, of course, that means preparing in advance the entangled pairs, just changing the image on one side and recording the result on the other side could be made at a pre set time.

 (So no need to transmit synchronisation information at all time through conventionnal means) 

still, it's just an hypothesis :) guess either slowing down the light or moving the medium containing it would break the entanglement anyway :)

Edited by sgt_flyer
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5 hours ago, K^2 said:

Educated guesses, since experiments in this regard are rather limited. (You can "fake" a time loop in some optical setups with lasers, but it's not exactly the same.) Nonetheless, all of the theory that doesn't blow up seems to suggest that observer would encounter history that's only consistent so far as his own timeline is concerned. It's easiest to interpret via MWI, because you can think of contradictions as observer simply encountering different parallel timelines, but the gist is the same in Copenhagen.

In other words, no fading photographs, Marty McFly style. Instead, you'll just have a piece of documentation or memory from your other visit to the same period that doesn't match what's currently happening.

If you subscribe to Copenhagen interpretation, or any other interpretation involving collapse, from perspective of other observers, a traveler who steps out of a CTC wormhole might as well be a random quantum fluctuation. Astonishingly unlikely one, but that's the sort of stuff you get in your QM when you construct time loops. Honestly, time travel will ever only make complete sense to the traveler.

How would that be a threat to the rest of reality, then? If you can't change the past, then causality is effectively maintained.

Also, the whole Novikov principle suggests to me that free will is an illusion. If the future is dependent on past events, and the future and past can interact, but neither can be changed, then isn't everything in between already established? Time travel would be more like splicing a bit of film from later in the movie in between the current frames.

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