And after
reading that, i still have NO idea WHAT they did, HOW they did it and what useful technology might be available because of it.
Quantum anything just breaks my brain.
Boffins at the US National Institute of Standards and Technology (NIST), collaborating with Japan's Nippon Telegraph and Telephone Corporation (NTT), have quadrupled the farthest distance quantum information has been "teleported". Quantum teleportation, of course, is not a matter of making physical matter dematerialise and …
One practical application of such (aside from calculating factors over millions of digits) would be the elimination of the thing we call "bandwidth". Imagine, if you will, instant communication of any amount of data over any distance.
As an example, it takes around 11 minutes (I believe) to transmit commands to a Mars rover and another 11 minutes for it to acknowledge. With quantum communications that latency wouldn't exist.
It's not instant.... The photons travel at light speed. And as light speed is finite, it leads to the wonderful world of spacetime. Minkowski got the handle on this from expanding on Einstein's theories of special relativity and incorporating the theories of Lorentz. ie: mines bigger than yours but only in a different frame of reference. ;-)
Quantum interference happens all the time, a measurement which collapses the wave packet of an entangled photon does not have to be made by humans. Why do we think we are so special? Trees do fall over in the forest when no one is watching.
David Deutsch's theories are interesting too.
I am not so smart my mind is open and I love this stuff. I just wonder how much of this quantum computing and teleportation is our Universe and many other Universes jointly conspiring to take us for a ride. When the real answer lies in a bottle of Shiraz.
It can be instant - transmit a constant stream of entangled radio waves to mars, keep the other half on a loop (the tricky bit*) then change the state of looped photons that are 10:59 minutes old using an input photon as described in the article - the radio photons 1s away from mars change state.. and voila, 1s lag to mars (or anywhere).
* Maybe all that stuff about reducing light down to walking speed in bose-einstein condensates or what have you could make the light containable for a few minutes...
No, that doesn't work. Which to me means quantum entanglement doesn't really work. Mainstream quantum physicists would offer some other explanation, perhaps relating to the "speed of information". But personally I think it's more likely just a big misunderstanding.
No. It's not that Quantum Teleportation, Quantum entanglement is like two identical packs of randomly shuffled cards, you don't know the state till you look. You can't actually send information that way. This does nothing whatsoever for speed (still light speed) or bandwidth. It's about encryption and security, knowing if the message has been tampered with.
Imagine, if you will, instant communication of any amount of data over any distance.
Adnim was the first in here to contradict your view that it opens up the idea of instant communications, but didn't explain why. I'll give it a shot.
First, there's the concept of "spooky action at a distance" whereby measuring one half of entangled pair instantaneously(*) causes the other half to settle on a value. This all happens in the quantum realm where the pair exists in a "superposition" of states before measurement and measurement "causes" (**) it to collapse into a single state.
Where it gets tricky is trying to use this for communication. If Alice and Bob have some method of producing a stream of entangled pairs and transporting both halves, you might think that some information can be encoded in each pair that the other party can read. In fact, that's not the case: the value of a measurement at either end has zero intrinsic informational content at all. The problem is that if you try to incorporate some information into the pair, then it counts as a measurement and the system as a whole collapses into a classical, non-quantum state.
But that doesn't mean that quantum effects can't be used as part of a communication scheme. The idea here is that Alice and Bob both set up similar apparatus for measuring some property of the entangled pair. Usually entangled photons are used, and the measuring apparatus involves using polarising filters that can be rotated. When the photon is measured at the receiving end, this measurement has no intrinsic information content since the receiver has no way of knowing how the sender set up their polarising filter. It's only by sharing their setup and results after the experiment that Bob can know what Alice was trying to encode, and that communication has to be purely classical and so is limited by the speed of light. Each trial like this has a 50% chance of not providing any information at all due to the random alignment of Bob's filter, so they need 2n trials to send n bits. Also, 2n bits need to be sent along the classical channel for each trial.
The benefit of "quantum" information transfer isn't that it's faster than light, but that it's impossible to eavesdrop without collapsing the state of the system before Bob gets to read the state of it. Plus, it's a validation that quantum effects are actually real.
* or nearly instantanous, as far as we can measure, but definitely faster than the speed of light. See
http://www.gizmag.com/quantum-entanglement-speed-10000-faster-light/26587/
** "causes" is in quotes because this isn't classical causality. We can only strictly describe the how measurement and collapse are related with a weaker "where this, also that" construct. This also opens up huge questions about how classical physics relates to the quantum world and what, in fact, the nature of things really is---the various Many Worlds theorems arise because of this fundamental gap in our understanding of how quantum states collapse.
What stops Mallory from reading the stream and re-sending classical photons of the same polarization?
Physics.
There's a good two-page discussion of the polarization QC technique in Applied Cryptography which I'm not going to try to condense into a forum post. But briefly:
- A polarized photon has some probability of flipping polarization. That's why, when you have two polarizing filters at 45 degrees, you get 50% of the light passing through both.
- Alice and Bob actually use polarization filters on two bases. Call them "horizontal/vertical" and "diagonal". So there are four settings for each filter: 0, 45, 90, and 135 degrees.
- Alice transmits a stream of photons with random polarization. (She records which polarization she used for each photon.)
- For any given photon, Bob can try to measure on the horizontal-vertical basis or the diagonal one. He can't measure both; the first attempt is a measurement and collapses the waveform. If Bob chooses h-v and the photon is polarized at 0 or 90 degrees, he sees the polarity. If the photon is polarized at 45 or 135, he gets a random result. And he can't tell whether a given result is correct (because he used the right polarity) or random (because he used the wrong one).
- So Bob sets up a series of detector settings and runs Alice's photon stream through it. He gets a series of polarization values in {0,45,90,135}; on average about half of them will be correct.
- Bob sends his filter settings (not his results) to Alice, over an insecure channel.
- Alice tells him which settings were right. Now both Alice and Bob know the polarization of the photons for about half the stream. They convert those polarizations to {0,1} and they have about half as many secret bits as there were photons in the stream.
Say Mallory intercepts the stream. Mallory can only obtain about half the polarizations correctly, so is unable to reproduce Alice's stream.
Good explanation. The two-axis thing was the critical detail I was missing.It does sound like it would work, provided Mallory can't falsify the insecure communications too. Though to my mind, this example has more to do with the uncertainty principle than entanglement or "teleportation".
Quantum Physics is so hard, even Quantum Physicists don't understand it!
How very yesterday.
The quantum mechanical formalism doesn't support our intuition, nor does it elucidate the key concepts that govern the behaviour of the entities that are subject to the laws of quantum physics. The arrays of complex numbers are kin to the arrays of 0s and 1s of the early days of computer programming practice. In this review we present steps towards a diagrammatic `high-level' alternative for the Hilbert space formalism, one which appeals to our intuition. It allows for intuitive reasoning about interacting quantum systems, and trivialises many otherwise involved and tedious computations. It clearly exposes limitations such as the no-cloning theorem, and phenomena such as quantum teleportation. As a logic, it supports `automation'. It allows for a wider variety of underlying theories, and can be easily modified, having the potential to provide the required step-stone towards a deeper conceptual understanding of quantum theory, as well as its unification with other physical theories. Specific applications discussed here are purely diagrammatic proofs of several quantum computational schemes, as well as an analysis of the structural origin of quantum non-locality. The underlying mathematical foundation of this high-level diagrammatic formalism relies on so-called monoidal categories, a product of a fairly recent development in mathematics. These monoidal categories do not only provide a natural foundation for physical theories, but also for proof theory, logic, programming languages, biology, cooking, ... The challenge is to discover the necessary additional pieces of structure that allow us to predict genuine quantum phenomena.
Wow! That scored 4 on the Plain-English meter and 97 on the Gobbledygook meter! It would have got a 100 if it had used Paradigm and Synthesis.
I will be using the text above in our companies bid for the F-35 short range data port. I need at least 5 pounds of text to justify an IR comm link (like your TV remote from 1981) because they don't trust/understand Blue Tooth.
They never read more than the first three pages and glance and the TOC anyway.
/sarcasm... or not? You decide.
"Can't be instant, surely, since that would require the information about the state change to travel faster than light?"
My (admittedly very basic) understanding of this is YES, the information about state change does happen instantaneously. But the communication itself cannot be faster than light, because the photons are entangled at the same location and cannot be moved away from each other faster than the speed of light.
the information about state change does happen instantaneously
Not quite. Measuring one of the pair causes the other to collapse instantaneously, and tells you what you would know if you were in a position to measure the other; but no information is transmitted, instantaneously or otherwise.
"Can't be instant, surely, since that would require the information about the state change to travel faster than light?"
As I understand it (ie not at all), the information isn't really travelling, the entangled particles are a single whole/system/whatever. They've done experiments showing the effect happening vastly quicker than light could travel the distance between said particles, apparently with zero delay (to the best it can be measured, anyway).
"Can't be instant, surely, since that would require the information about the state change to travel faster than light? But I agree, it makes my brain hurt."
That's one of the (many) paradoxes of quantum mechanics. Einstein thought that if you look at the state of one of a pair of entangled particles, then you instantly know the state of the other particle, because their paired states have already been decided in the past (e.g. if you find a left shoe at the back of a cupboard, you instantly know that the other one that you can't find is a right shoe.)
Niels Bohr thought differently - that due to the peculiarities of quantum physics, the state of the first particle wasn't 'concrete' (for want of a better word) until it was observed, but that you could still be instantly certain of the state of the second particle, even if it was some distance away i.e. the second particle somehow could tell the state of the first particle faster than the speed of light, which goes against Einstein's theory of general relativity (hence his 'spooky action at a distance' quote.)
I've no idea if this settled the argument for good (mainly because I can't even begin to understand the maths or the physics), but John Bell came up with an equation in the 60's that predicted a test of whether Bohr or Einstein was correct. Using entangled light quanta in a laser, John Clauser in California and later Alain Aspect in Paris (and quite a few others since) used this equation to experimentaly prove that Bohr was right, that entangled pairs somehow do seem to know the state of their twin instantaneously.
It doesn't mean that we can travel faster than the speed of light in a vacuum through space-time. But it does mean that we can't tell what the **** is going on at the quantum level.
And now my brain hurts as well. Thanks :)
A sensible way to look at entangled particles is to imagine them as a single wave that spans across a large distance. The wave is the particle wave you can calculate according to the laws of quantum physics, and the wave contains all information about all possible states the particles might be found in. If you make a measurement, you collapse the wave onto a particular state of the particles -- and because you collapsed the complete wave this effects the particle property at the faraway other end of the wave.
It's no rocket science, and it's also not classical physics.
In my hazy understanding of the topic I believe you need to confirm the data received via entanglement via classical means as well as sending one of the tangled pair out. If someone fancies reading the wikipedia non-technical summary I'll just leave it here:
https://en.wikipedia.org/wiki/Quantum_teleportation#Non-technical_summary
You can't actually send information at all, whatsover, purely by having two separated particles at each end that are quantum entangled. It may be the effect of reshuffling the pack is instant, but you have no way at the receiver of knowing, thus no method to send a signal. This is about sending photons (a little slower than light speed as it's in a fibre). It's about security, not speed.
It's instant quantum information transfer, but not instant (classical) information transfer. The difference has to do with the probabilistic nature of quantum physics and the thing you call information, e.g., bits, is not transferred in teleportation.
Quantum physics is a mathematical description of matter and the math tells us that you can transfer classical information only with the speed of light or slower. No quantum trick can help you with that. Full Stop.
When, oh when, will they start teaching this at Kindergarden to save us this endless discussion among otherwise quite reasonable men.
Lads I'm fairly sure* that information can not be communicated any faster than C. The Entangled photon still has to be transmitted across the wire/fiber at relativistic speeds. I think it's value to crypto comes from the fact that it cant be fudged with along the way without messing up the entanglement.
*Not a quantum boffin, this stuff hurts my brain too.
"I think it's value to crypto comes from the fact that it cant be fudged with along the way without messing up the entanglement."
That's my recollection, too, but there is nothing in the diagram that makes that point, which is a pity. As it stands in the diagram, the whole thing is open to a MitM attack. I assume there is an answer to that, but it doesn't appear to be in the article so I'm left thinking " Umm ... quantum ... magic .. awesome stuff ... too complicated for my little brain".
One shouldn't *have* to go googling in order to understand why an article is worth reading.
No, both are in a linked state ("entangled", geddit?), so if you examine the state on side A, you INSTANTLY KNOW (evidently) what the state side B must be in. The fun is only that the state on either side is undefined (only the common state is defined) until observation on side A or side B actually takes place. The extremely fun thing is that the order of observation can be arbitrarily shuffled by choosing the appropriate relativistic reference frame (A before B, B before A, A simultaneous to B - results must be the same).
It's really very simple. COUGH
Wait, wait, wait.
So you're telling me that something as confusing as quantam entanglement can be explained using the shell game? I.e. the pea could be under any shell no matter how far apart they are. But, if you lift one shell and find the pea, you instantly know that the other shells have nothing under them.
Unfortunately not - that's what Einstein believed and the Bell inequalities were used to experimentally disprove. The pea would be a hidden variable. Things are spookier than that!
There is definitely one thing than travels faster than ordinary light though - monarchy.
Whereas having to subtract a well-chosen infinity from every calculation in order to get the right answer isn't magic at all. It's straightforward, in fact.
Sorry, but whilst I'm happy to accept that Bohm isn't any better than the conventional interpretation, I'm not happy to accept that it is much worse.
QM is straight-arse extension of classical probability. No infinites involved as no Quantum Field Theory yet. Bohm didn't get anywhere near QFT as far as I know.
It's been some time, but I remember bohmian interpretation being very much worse, because in disagreement with experiment and/or inconsistent. More here.
If I understand the article (which I probably don't) the 'teleportation' happens via a fibre optic cable. Now, the Enterprise didn't have to connect a fibre-optic cable to the Klingon bird of prey to teleport people backwards and forwards, did it? It sounds like this is teleportation in the same sense that Welsh Water teleport water from the reservoir to my home via a pipe.
Wait ... a third of the data just went ... somewhere else?
Even Target didn't leak data that badly, and we had a shrewd idea where it all went too, once we knew it had gone missing in the first place.
Also not keen on this rather wishy-washy "sometimes can't detect the photons" get-out clause. Was the quantums generator manufactured by Volkswagen Digital Evasion LLC by any chance?
Quantum teleportation is not: "a matter of [...] transporting information", but it is only: transporting quantum information. The two are quite different!
What is the difference, you ask? I'll explain it for one last time, especially for those slow kids in the back.
Quantum information is information about the quantum state of a particle. With some tricks, you can create two entangled particles which are in identical or complementary quantum states. If you measure a quantum state property of one particle, you also know something about the quantum state of the other. It does not matter where that other particle is, so you can separate the particles by a great distance, measure your particle property here, and magically know about a particle property far away. This is like putting a green and red card in identical envelopes, sending one of them to Australia, and then magically (and instantly) knowing the card color in Australia when opening your envelope and checking your own card color. Note: there has been no information transfer to Australia, but if you now send another letter telling your Australian partner that blue means yes and red means no, you have performed the equivalent of quantum encryption.
Congratulations, you now understood the easy part of quantum transfer: its a way to send a decryption key to a partner ahead of the message. As opposed to the colored card, the particle will be destroyed if somebody else looks at its properties, so the key cannot be easily intercepted. Now you understand why people are enthusiastic about quantum encryption.
We now established that quantum teleportation (the only type we know of) allows you to predict some measurement outcome for a faraway particle just like sending cards around. But here comes the quantum magic: If I measure a quantum property the measurement can affect other quantum properties. You measure a property here, it must affect also the complementary property in Australia. Let's go through this with the Heisenberg uncertainty as an example: Heisenberg said that the product of position x and impulse p uncertainty must be bigger or equal to a constant: $\Delta x \cdot \Delta p >= \hbar /2$. If I measure the precise impulse of a particle, I make it impossible to measure the precise position of said particle and also of any entangled partner particle elsewhere. My measurement therefore magically affects measured properties elsewhere, it's "spooky action at a distance". If my Australian partner looks at one particle he won't notice anything, he'll find the particle in some spot. But if he looks at many particles, he'll now find out that they arrive all over the place (there now is a big uncertainty about their position because I measured the impulse of my particles).
Let me translate this into the card example: Assume there is a shape-size uncertainty product in the cards I sent to Australia. If I start measuring the size of my cards, my Australian partner will suddenly see that the shapes of his cards are much more irregular that they used to be. Doesn't quite work with classical particles (cards), does it? But it works with quantum particles.
Now to the VERY IMPORTANT question of information transfer: The quantum teleportation affects some property of a far away particle, but it's just a probabilistic effect. The Australian partner must look at many cards to see that the shapes became irregular. I cannot control the shape of his card and therefore I cannot send classical information (i.e., information as you understand it).
Got it? Congratulation, you can pick up your physics degree on the way home.
This is like putting a GREEN and red card in identical envelopes, sending one of them to Australia, and then magically (and instantly) knowing the card color in Australia when opening your envelope and checking your own card color. Note: there has been no information transfer to Australia, but if you now send another letter telling your Australian partner that BLUE means yes and red means no, you have performed the equivalent of quantum encryption.
So WTF does Green mean?????
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