[scratt]

http://www.livescience.com/strangene...ion-atoms.html

A very interesting article.

Although it is talking about teleportation I found it interesting because of the possible applications for the WWW and also Quantum computing.

One thing I had never quite grasped was why we could not use this to transfer information and therefore eventually people copies of people at infinite speeds around the Universe. i.e Crossing the light speed barrier. I do *know* the reason, but never quite *understood* it: Basically I understood that we still have to have a speed of light connection between the two instantly updated quantum 'nodes' otherwise it does not work, but didn't quite understand what that "Lo-Tech" connection was for.

This article is the clearest way I have ever seen it explained.

Again, this is all of course based on the assumption that it's not all a bunch of crap, and we are not stupid monkeys, missing something very fundamental and obvious, and therefore drawing the wrong conclusion overall about Life. The Universe. And Everything!

I have to admit as much as I want String theory, Bubbleverses and Quantum physics to all pan out, sometimes it's just so strange, and nature is normally so neat and tidy, I have to wonder if we really are missing something very basic.

Anyway. If you enjoy this sort of thing it's an interesting read.

[ezkcdude]

I've downloaded the Science article "Quantum Teleportation Between
Distant Matter Qubits". If anyone wants it send me a pm.

Abstract:

Quantum teleportation is the faithful transfer of quantum states between systems, relying on the prior establishment of entanglement and using only classical communication during the transmission. We report teleportation of quantum information between atomic quantum memories separated by about 1 meter. A quantum bit stored in a single trapped ytterbium ion (Yb+) is teleported to a second Yb+ atom with an average fidelity of 90% over a replete set of states. The teleportation protocol is based on the heralded entanglement of the atoms through interference and detection of photons emitted from each atom and guided through optical fibers. This scheme may be used for scalable quantum computation and quantum communication.

[curiousuburb]

Ah quantum entanglement... what Einstein called 'spooky interaction at a distance'.

Quantum cryptographers have been playing with qubit states for a while.

IIRC, the 'teleportation' of 'information' has been tested across the globe (infinite distance theoretically identical). The term 'information' is a bit more loosely defined than most prefer, though.

Some work has also been done using BoseEinsteinCondensates slowing light to a stop and teleporting or 'transferring spin' with additional reference beams by Dr. Lene Hau at Harvard.

Fascinating, if headbending stuff.

Still some way to go before Emory Erickson
.

[Moogs]

A bit over my head but vaguely understood. Cool stuff. What are the chances Apple will use this technology in X-Serve by 2010?

[billybobsky]

all of these experiments are not really teleportation in the classic sense... what they are is creative experiments proving that a certain detected quantum state means that two atoms are in an either or state... It has yet to be proven that you can transfer useful information this way -- remember this experiment has only 90% fidelity of the 1/thousands of attempts -- it isn't as if you can use this setup to "send" information...

[tomoe]

Originally Posted by billybobsky all of these experiments are not really teleportation in the classic sense... what they are is creative experiments proving that a certain detected quantum state means that two atoms are in an either or state... It has yet to be proven that you can transfer useful information this way -- remember this experiment has only 90% fidelity of the 1/thousands of attempts -- it isn't as if you can use this setup to "send" information...

So I guess it won't be making it into X-Serve by 2010 then?

[scratt]

Originally Posted by billybobsky all of these experiments are not really teleportation in the classic sense... what they are is creative experiments proving that a certain detected quantum state means that two atoms are in an either or state... It has yet to be proven that you can transfer useful information this way -- remember this experiment has only 90% fidelity of the 1/thousands of attempts -- it isn't as if you can use this setup to "send" information...

I think the idea is that you can.

The reason I crossed out people in my first post is simply because of this.
With this teleportation will be more like transmitting a fax, is the way I understand it. Several SciFi stories have touched on it. Star Trek does also, but it's not shoved in your face. Basically if transporting people or materials you are effectively recreating a facsimile and then we have the moral dilemma of what to do with you after your facsimile takes over your life on Mars.

At the end of the day teleportation in the traditional sense is not possible and the idea proposed in movies like The Fly, or The Prestige is more the reality.

In my mind, assuming that this could one day give us instantaneous transmission of information I am more interested in the computer aspects of it. The idea of a super CPU - GPU setup which with one parity line and a pool of quantum "thingymajigs" can shift infinite amounts of data into screen memory in effectively 0 time.

My understanding was that it was a way to get past the speed limit imposed by electrons and even light in our current computer architectures... and to massively parallel operations both by breadth and also real distance.

[ezkcdude]

Originally Posted by billybobsky all of these experiments are not really teleportation in the classic sense... what they are is creative experiments proving that a certain detected quantum state means that two atoms are in an either or state... It has yet to be proven that you can transfer useful information this way -- remember this experiment has only 90% fidelity of the 1/thousands of attempts -- it isn't as if you can use this setup to "send" information...

Just needs more parity qubits!

[billybobsky]

Originally Posted by scratt My understanding was that it was a way to get past the speed limit imposed by electrons and even light in our current computer architectures... and to massively parallel operations both by breadth and also real distance.

No... regardless of whatever beliefs you may hold, unless we seriously alter the geometry of the local universe we aren't going to beat the speed of light. These events aren't instantaneous -- think about the experiment in this paper -- the entangled state is implied by a detection of two photons past the beam splitter -- this occurs only once every several thousand rounds of trying. I say implied, because the possibility for the entangled state NOT to exist at that point is nil. It is entangled because the experimentalists cannot say a priori which atom generated which photon -- this is not saying that these two atoms are communicating with each other (though they could be, at the speed of light). I have not seen any experiment to prove that the generation of the entangled state is not the result of a pre-selection of a particular state and we simply don't have the means to detect that state simultaneously -- meaning, we go with the assumption that the state is one of two possibilities and that the next tweak we do to the system "generates" the rule abiding state (90% of the time in this experiment likely due to temperature fluctuations).

Another way to look at it is that the atoms are releasing photons independently throughout the entire course of the experiment, and every once in a while they release them in a certain manner that allows detection of a certain state that has two ways of being possible. It follows that when you go to check to see if the atoms are in the right states to generate one of those two possibilities, it will be the case. This is what they are calling entanglement...

[scratt]

Originally Posted by billybobsky No... regardless of whatever beliefs you may hold, unless we seriously alter the geometry of the local universe we aren't going to beat the speed of light.

My understanding was that the speed of light communication was required as a sort of parity check, but between entangled particles the communication was instantaneous. Isn't that the whole point of Quantum entanglement? The fact that we know these things change instantaneously thus circumventing the current laws of physics as we understand it? And we cannot explain that with the current laws we have?

I thought the whole point of this was that instantaneous bit.

I understand that there are different theories. But that the generally accepted fly in the ointment was that you could not make sense of the results / confirm them without the side communication.

So in that sense we can't beat the speed of light, but Quantum entanglement does.
We have yet to prove if we can make use of it, or whether it really works, but have no other better explanation...

I agree that it all seems a bit smoke and mirrors, which is why I am not convinced anyway.

The research team says their finding disproves the more comprehensible hypothesis–that the particles were sending signals at faster-than-light speed–and instead supports the stranger theory of instant communication. Dr Terence Rudolph of Imperial College, London, remarks that “any theory that tries to explain quantum entanglement… will need to be very spooky - spookier, perhaps, than quantum mechanics itself” [Telegraph].

btw. Thanks for the article ezkcdude. It's on my iPhone for bedtime reading..

[ezkcdude]

It seems to me like you're saying their experiment is like predicting the outcome of a coin toss. Of course, you're going to be right some of the time, but it's not because you had any special information. You just know there are two possible outcomes.

Or maybe it's nothing like that...

[billybobsky]

Originally Posted by scratt My understanding was that the speed of light communication was required as a sort of parity check, but between entangled particles the communication was instantaneous. Isn't that the whole point of Quantum entanglement? The fact that we know these things change instantaneously thus circumventing the current laws of physics as we understand it? And we cannot explain that with the current laws we have?

Here's my take... The state of the two atoms is set not when it is measured, but rather when they release the photons. Measurement just clarifies which of two states it WAS and does not, in fact, set the result of the other atom.

I thought the whole point of this was that instantaneous bit. I understand that there are different theories. But that the generally accepted fly in the ointment was that you could not make sense of the results / confirm them without the side communication.

Not really... They are playing around in a sand box that exists solely because in theory in quantum mechanics a state isn't set until it is measured. Now what constitutes a measurement has never really been defined. Releasing a photon indicates something about that particular atom, meaning it could very well be a measurement.

So in that sense we can't beat the speed of light, but Quantum entanglement does. We have yet to prove if we can make use of it, or whether it really works, but have no other better explanation... I agree that it all seems a bit smoke and mirrors, which is why I am not convinced anyway.

No, there really is no way to beat the speed of light; even in this experiment nothing is proven instantaneous since measurements are occurring on a slower than light speed rate. I suspect that if there is entanglement it is at light speed. Now the problem with this theory (if long range entanglement exists, and really, we haven't shown it to be real) a lot of science remains to be done on exactly what is carrying that information. Regardless, I think the appearance of spooky action at a distance is distinct from actual spooky action at a distance.

[billybobsky]

Originally Posted by ezkcdude It seems to me like you're saying their experiment is like predicting the outcome of a coin toss. Of course, you're going to be right some of the time, but it's not because you had any special information. You just know there are two possible outcomes. Or maybe it's nothing like that...

No, it's not a prediction...

When a particular state is detected, Atom A and atom B almost always have quantum states that make that detected state possible (it should be always)... This is somewhat obvious. It's like hearing people calling heads or tails and "predicting" that they are playing with a two sided coin while knowing that they are playing with a coin.

[Enki]

The entangled qbits will instantaneously communicate over those great distances seemingly violating transfer of information at the speed of light. But the catch is you have to physically transfer one of those qbits to where it will receive the information. That part still takes damn near forever. And I think it's more likely that we will develop some alternate folding method of travel before the traveling paired qbit arrives at the other "side" of the universe. That means the folding ship gets there first. Sure it could carry qbits too, but why bother at that point?

[scratt]

Originally Posted by Enki The entangled qbits will instantaneously communicate over those great distances seemingly violating transfer of information at the speed of light. But the catch is you have to physically transfer one of those qbits to where it will receive the information. That part still takes damn near forever. And I think it's more likely that we will develop some alternate folding method of travel before the traveling paired qbit arrives at the other "side" of the universe. That means the folding ship gets there first. Sure it could carry qbits too, but why bother at that point?

This is exactly my understanding. Which is why I am confused when people keep saying that the transmission is not instantaneous... (I am not saying this is fact, or has been proven conclusively, but I thought it was the current theory.)

Originally I know people were theorizing about being able to send people / things / information over huge distances.
But that the problem with that is that you would have to entangle the qbits here, together, and then send one half of them to the destination. In theory I suppose you could put a 'qbit receiver and facsimile' machine on Mars, and transmit from Earth to it, and have instant radio comms or even object transmission. But then there was the problem of knowing when to read the qbit, or the inaccuracy or something.. and I thought that was where the side transmission at light speeds was the only solution, for now.

I know that it's all a lot of theories with some pretty rudimentary (by fscking advanced Physicists standards) lab experiments right now. And even still I think it's possible that we might go.. "Oh, shit, yeah. We missed this or that and it's not actually how it works, based on what we now understand.", at some point.

But my understanding was definitely that right now entangled qbits either do have an instantaneous symmetry, or to paraphrase Einstien, "something spooky is going on".

[billybobsky]

there are several problems with your interpretation, scratt.

no information can be transfered. the success of the experiment is known only at best at the speed of light. etc.

I think there are several problems viewing this as an instantaneous affair. All entanglement says is that by making two measurements (one to confirm that an entangled state exists, and second what the wavefunction of one entangled particle is), you can know what another particle did (this actually isn't contradictory to the two measurements give two unknowns). The entanglement process itself is limited to the speed of light, and thus effectively nothing is instantaneous. The instantaneousness of the change of state only comes out of the lack of knowledge that humans have before they make the second measurement.

[scratt]

Originally Posted by billybobsky there are several problems with your interpretation, scratt.

I am confused. Can you clarify for me. It seems Enki has the same interpretation as me.
Is his interpretation also wrong?

Originally Posted by billybobsky no information can be transfered. the success of the experiment is known only at best at the speed of light. etc.

When we send electrons down a wire it's not actually the same electron that you send that arrives at the destination AFAIK. So in effect we don't really transfer anything there. It's more like a FIFO. Right?
Eventually the electron you sent will get there, but probably as the result of a completely unrelated electron being shoved down the other end of the wire. With lasers I guess it's a case of whether the thing is a particle or a waveform, and even then waveforms take time to propagate. So with lasers and fiber optics that is also kind of a FIFO, whereas qbits and entanglement we keep getting told 'instantaneous'.

I know that's not the same, but what I am getting at is information is not tangible. So if the state in one qbit mirrors the state in another, and you do that enough times in serial then surely you are transferring 'information'?

Again, perhaps I misunderstand. So please elaborate on what you mean.

Originally Posted by billybobsky I think there are several problems viewing this as an instantaneous affair. All entanglement says is that by making two measurements (one to confirm that an entangled state exists, and second what the wavefunction of one entangled particle is), you can know what another particle did (this actually isn't contradictory to the two measurements give two unknowns). The entanglement process itself is limited to the speed of light, and thus effectively nothing is instantaneous.

How so?

Originally Posted by billybobsky The instantaneousness of the change of state only comes out of the lack of knowledge that humans have before they make the second measurement.

[ezkcdude]

This quantum entanglement stuff is spooky.

[scratt]

Totally. And because of that sometimes it's hard to understand people's explanations (mine included).

@billybobsky:
What I am trying to do is understand exactly what you are saying.
What I am unsure of (with all due respect) is whether you really know your stuff, or if you are putting your interpretation on this.

You are speaking in quite an authoritative tone, but I am not quite grasping what you mean for some of it.

[curiousuburb]

Feynman once said to a class of students:

Originally Posted by Richard Feynman I think I can safely say that nobody understands quantum mechanics.

See also the Feynman sections here

[ezkcdude]

So, getting back to entanglement. Am I safe to say that although the observation of entanglement is a fact, the underlying theory (causation) remains unknown?

[scratt]

I can't authoritatively say (obviously), but that is certainly my understanding.

At the back of my mind I still have to wonder if it's like one of those bugs you find in your code years after a project is finished, when you realize that although it was doing what you expect, it certainly was not doing it the way you thought you coded it. erm.... If you get my meaning!

[ezkcdude]

The entanglement arises when the two particles are created, right?

So, it would make sense to me if the state of each particle is deterministic, but that one could not be affected by changing the other. That probably makes no sense, so let me attempt to make a twin analogy (aha, twins are not just for relativity anymore!):

Let's say that we have a set of anti-identical twins; instead of being exactly the same, they are exactly the opposite. One twin has blue eyes, the other has brown. One twin is blonde, the other brunette. So, for example, knowing that the twins are opposites, it would be easy to predict (or observe) that when one twin begins to grow chest hair, the other begins to grow boobs. However, in this hypothetical scenario, if we change a certain characteristic about one twin, say changing their hair color, that does not result in a change in the other twin - because we have broken the determinism of the system.

My question about entanglement is thus: If we (actively) change the state of one of the particles, does the other particle change (and is it even possible to change the state of one of these particles)? Or is it the case that we simply can observe a change in the other particle, when the first one changes state of it's own "volition", so to speak. If the latter is true, then it seems to me the matter (literally) is not as spooky as I thought.

p.s. Scratt, does this brainy convo make up for the Israel thread?

Edit: I just realized I'm not the first to make this twin analogy. Here's a good read.

[billybobsky]

scratt, I have taken a large number of courses that pivot around quantum theory. i cannot say i understand how quantum works, but i have an intuitive feel for how it goes.

Originally Posted by scratt I am confused. Can you clarify for me. It seems Enki has the same interpretation as me. Is his interpretation also wrong?

It's the idea of instantaneous that is wrong. it isn't an instantaneous change, its an instantaneous additional piece of information. my argument is that this shouldn't be surprising, since we are effectively measuring the system twice, once in creating the entangled state, and a second time to figure out what state our atom is in.

When we send electrons down a wire it's not actually the same electron that you send that arrives at the destination AFAIK. So in effect we don't really transfer anything there. It's more like a FIFO. Right?

Well... wires are interesting because it is the field (voltage) we are sending as opposed to the electrons. Electrons aren't moving in AC on average... For DC, it is the field that matters, but over time the electrons will have been displaced. The movement of the electrons through the wire is governed, however, by the speed of the field (which happens to be the speed of light).

Eventually the electron you sent will get there, but probably as the result of a completely unrelated electron being shoved down the other end of the wire. With lasers I guess it's a case of whether the thing is a particle or a waveform, and even then waveforms take time to propagate. So with lasers and fiber optics that is also kind of a FIFO, whereas qbits and entanglement we keep getting told 'instantaneous'.

lasers... its the same photon. that much is known -- otherwise none of these experiments we are discussing tangentially would work.

I know that's not the same, but what I am getting at is information is not tangible. So if the state in one qbit mirrors the state in another, and you do that enough times in serial then surely you are transferring 'information'?

The reason it isn't the same is that in electricity and light, the generator A can change what observer B sees. This is actually impossible in entangled states. Quantum mechanically impossible -- as in the quantum mechanical state of an entanglement is a sum of two distinct states that measurement reveals to be one or the other. There is no way for person A to change the answer they get upon measurement which allows them to know what person B will observe. Theoretically, you would have to have something far far more complex than a simple entangled state to allow person A to knowingly change an entangled state (in fact, I think you would have to pitch quantum theory) so that person B's observation isn't a given, but is mutable. (ezkcdude this should answer your question).

How so?

You have to consider what it takes to create an entangled state. Almost all observations so far of these states have been limited to photon production -- that is, the entangled state comes to exist only some small small fraction of the time during the release of pairs (or more) of photons. The entangled state doesn't come about 100% of the time and once you measure it, it is no longer entangled. We only know that the entangled state exists because of these photons, in point of fact, in the absence of these photons we could say nothing about both of the atom atom A and B with only one measurement of atom A (hence my contextualizing these results in the idea of two measurements giving you two unknowns). Basically, because a measurement means a setting of a state in quantum mechanics, these photons released that give rise to the entangled state are absolutely essential for that state's existence, and there is no faster experimental way to show that you have an entangled state -- and this makes the speed limit of knowing the speed of light.

[scratt]

Originally Posted by ezkcdude The entanglement arises when the two particles are created, right?

I don't know. I never actually considered that. Obviously the way these things are written up for mere mortals you sort of imagine a test tube with a couple of particles. But the truth is a lot more confusing / messy / whatever.
The way I read it two existing particles are entangled.

Originally Posted by ezkcdude p.s. Scratt, does this brainy convo make up for the Israel thread?

Nothing really to make up for IMO. This is *certainly* a more constructive use of our time!!

Originally Posted by ezkcdude Edit: I just realized I'm not the first to make this twin analogy. Here's a good read.

Interesting analogy. Yours had more boobs in it!

Originally Posted by billybobsky scratt, I have taken a large number of courses that pivot around quantum theory. i cannot say i understand how quantum works, but i have an intuitive feel for how it goes.

Fair enough. Great, so now we have someone with qualifications to blame any mistakes on.

Originally Posted by billybobsky It's the idea of instantaneous that is wrong. it isn't an instantaneous change, its an instantaneous additional piece of information. my argument is that this shouldn't be surprising, since we are effectively measuring the system twice, once in creating the entangled state, and a second time to figure out what state our atom is in.

I am going to have to read some more to understand how that ties up to how I understand it.
I am not disagreeing here at all. I just have a different interpretation.
I do understand very well about the effect of the observer on quantum results. So perhaps it ties into that.

Originally Posted by billybobsky The reason it isn't the same is that in electricity and light, the generator A can change what observer B sees. This is actually impossible in entangled states. Quantum mechanically impossible -- as in the quantum mechanical state of an entanglement is a sum of two distinct states that measurement reveals to be one or the other. There is no way for person A to change the answer they get upon measurement which allows them to know what person B will observe. Theoretically, you would have to have something far far more complex than a simple entangled state to allow person A to knowingly change an entangled state (in fact, I think you would have to pitch quantum theory) so that person B's observation isn't a given, but is mutable. (ezkcdude this should answer your question).

I'll leave this bit for now. But may come back to it later.
Again, I want to read some more before I comment, and the next bit is where my questions are..

Originally Posted by billybobsky You have to consider what it takes to create an entangled state. Almost all observations so far of these states have been limited to photon production -- that is, the entangled state comes to exist only some small small fraction of the time during the release of pairs (or more) of photons. The entangled state doesn't come about 100% of the time and once you measure it, it is no longer entangled. We only know that the entangled state exists because of these photons, in point of fact, in the absence of these photons we could say nothing about both of the atom atom A and B with only one measurement of atom A (hence my contextualizing these results in the idea of two measurements giving you two unknowns). Basically, because a measurement means a setting of a state in quantum mechanics, these photons released that give rise to the entangled state are absolutely essential for that state's existence, and there is no faster experimental way to show that you have an entangled state -- and this makes the speed limit of knowing the speed of light.

%0 is how you can say categorically that it's not instantaneous. I see that you can only get the info at the speed of light, and just for a moment getting rid of all the stuff required for the experiment, and imagining we just have two entangled particles, and special glasses that enable us to see them. If you change one, then what says that the other one is delayed by c/dist between qbits before it actually changes?

In short, even if I can only see the result because of photon release, but I have my qbit reciever on Mars, and the transmitter on Earth, and each contains one half of the pair of entangled particles, why can I not transmit one bit of information from Earth to Mars before my qbit devices disentangle (because of that one bit I just sent), and then I see the photon after it leaves my local qbit. That would still be effectively instantaneous when you consider how long light / radio takes to get to Mars from Earth.

[scratt]

Originally Posted by ezkcdude The entanglement arises when the two particles are created, right?

I don't know. I never actually considered that. Obviously the way these things are written up for mere mortals you sort of imagine a test tube with a couple of particles. But the truth is a lot more confusing / messy / whatever.
The way I read it two existing particles are entangled.

Originally Posted by ezkcdude p.s. Scratt, does this brainy convo make up for the Israel thread?

Nothing really to make up for IMO. This is *certainly* a more constructive use of our time!!

Originally Posted by ezkcdude Edit: I just realized I'm not the first to make this twin analogy. Here's a good read.

Interesting analogy. Yours had more boobs in it!

Originally Posted by billybobsky scratt, I have taken a large number of courses that pivot around quantum theory. i cannot say i understand how quantum works, but i have an intuitive feel for how it goes.

Fair enough. Great, so now we have someone with qualifications to blame any mistakes on.

Originally Posted by billybobsky It's the idea of instantaneous that is wrong. it isn't an instantaneous change, its an instantaneous additional piece of information. my argument is that this shouldn't be surprising, since we are effectively measuring the system twice, once in creating the entangled state, and a second time to figure out what state our atom is in.

I am going to have to read some more to understand how that ties up to how I understand it.
I am not disagreeing here at all. I just have a different interpretation.
I do understand very well about the effect of the observer on quantum results. So perhaps it ties into that.

Originally Posted by billybobsky The reason it isn't the same is that in electricity and light, the generator A can change what observer B sees. This is actually impossible in entangled states. Quantum mechanically impossible -- as in the quantum mechanical state of an entanglement is a sum of two distinct states that measurement reveals to be one or the other. There is no way for person A to change the answer they get upon measurement which allows them to know what person B will observe. Theoretically, you would have to have something far far more complex than a simple entangled state to allow person A to knowingly change an entangled state (in fact, I think you would have to pitch quantum theory) so that person B's observation isn't a given, but is mutable. (ezkcdude this should answer your question).

I'll leave this bit for now. But may come back to it later.
Again, I want to read some more before I comment, and the next bit is where my questions are..

Originally Posted by billybobsky You have to consider what it takes to create an entangled state. Almost all observations so far of these states have been limited to photon production -- that is, the entangled state comes to exist only some small small fraction of the time during the release of pairs (or more) of photons. The entangled state doesn't come about 100% of the time and once you measure it, it is no longer entangled. We only know that the entangled state exists because of these photons, in point of fact, in the absence of these photons we could say nothing about both of the atom atom A and B with only one measurement of atom A (hence my contextualizing these results in the idea of two measurements giving you two unknowns). Basically, because a measurement means a setting of a state in quantum mechanics, these photons released that give rise to the entangled state are absolutely essential for that state's existence, and there is no faster experimental way to show that you have an entangled state -- and this makes the speed limit of knowing the speed of light.

se, but I have my qbit reciever on Mars, and the transmitter on Earth, and each contains one half of the pair of entangled particles, why can I not transmit one bit of information from Earth to Mars before my qbit devices disentangle (because of that one bit I just sent), and then I see the photon after it leaves my local qbit. That would still be effectively instantaneous when you consider how long light / radio takes to get to Mars from Earth.

[scratt]

Originally Posted by ezkcdude The entanglement arises when the two particles are created, right?

I don't know. I never actually considered that. Obviously the way these things are written up for mere mortals you sort of imagine a test tube with a couple of particles. But the truth is a lot more confusing / messy / whatever.
The way I read it two existing particles are entangled.

Originally Posted by ezkcdude p.s. Scratt, does this brainy convo make up for the Israel thread?

Nothing really to make up for IMO. This is *certainly* a more constructive use of our time!!

Originally Posted by ezkcdude Edit: I just realized I'm not the first to make this twin analogy. Here's a good read.

Interesting analogy. Yours had more boobs in it!

Originally Posted by billybobsky scratt, I have taken a large number of courses that pivot around quantum theory. i cannot say i understand how quantum works, but i have an intuitive feel for how it goes.

Fair enough. Great, so now we have someone with qualifications to blame any mistakes on.

Originally Posted by billybobsky It's the idea of instantaneous that is wrong. it isn't an instantaneous change, its an instantaneous additional piece of information. my argument is that this shouldn't be surprising, since we are effectively measuring the system twice, once in creating the entangled state, and a second time to figure out what state our atom is in.

I am going to have to read some more to understand how that ties up to how I understand it.
I am not disagreeing here at all. I just have a different interpretation.
I do understand very well about the effect of the observer on quantum results. So perhaps it ties into that.

Originally Posted by billybobsky The reason it isn't the same is that in electricity and light, the generator A can change what observer B sees. This is actually impossible in entangled states. Quantum mechanically impossible -- as in the quantum mechanical state of an entanglement is a sum of two distinct states that measurement reveals to be one or the other. There is no way for person A to change the answer they get upon measurement which allows them to know what person B will observe. Theoretically, you would have to have something far far more complex than a simple entangled state to allow person A to knowingly change an entangled state (in fact, I think you would have to pitch quantum theory) so that person B's observation isn't a given, but is mutable. (ezkcdude this should answer your question).

I'll leave this bit for now. But may come back to it later.
Again, I want to read some more before I comment, and the next bit is where my questions are..

Originally Posted by billybobsky You have to consider what it takes to create an entangled state. Almost all observations so far of these states have been limited to photon production -- that is, the entangled state comes to exist only some small small fraction of the time during the release of pairs (or more) of photons. The entangled state doesn't come about 100% of the time and once you measure it, it is no longer entangled. We only know that the entangled state exists because of these photons, in point of fact, in the absence of these photons we could say nothing about both of the atom atom A and B with only one measurement of atom A (hence my contextualizing these results in the idea of two measurements giving you two unknowns). Basically, because a measurement means a setting of a state in quantum mechanics, these photons released that give rise to the entangled state are absolutely essential for that state's existence, and there is no faster experimental way to show that you have an entangled state -- and this makes the speed limit of knowing the speed of light.

OK. I did not realize that the entangled state gets destroyed when they give off photons. That kind of messes up the idea of sending a qbit receiver with the next Mars mission, and using it to have instant radio comms. Because the first bit (literally) of info would break the receiver! Obviously that is complete science fiction anyway. But you get that, I am sure.

The bit I still am confused on is how you can say categorically that it's not instantaneous. I see that you can only get the info at the speed of light, and just for a moment getting rid of all the stuff required for the experiment, and imagining we just have two entangled particles, and special glasses that enable us to see them. If you change one, then what says that the other one is delayed by c/dist between qbits before it actually changes?

In short, even if I can only see the result because of photon release, but I have my qbit reciever on Mars, and the transmitter on Earth, and each contains one half of the pair of entangled particles, why can I not transmit one bit of information from Earth to Mars before my qbit devices disentangle (because of that one bit I just sent), and then I see the photon after it leaves my local qbit. That would still be effectively instantaneous when you consider how long light / radio takes to get to Mars from Earth.

[billybobsky]

Originally Posted by scratt %0 is how you can say categorically that it's not instantaneous. I see that you can only get the info at the speed of light, and just for a moment getting rid of all the stuff required for the experiment, and imagining we just have two entangled particles, and special glasses that enable us to see them. If you change one, then what says that the other one is delayed by c/dist between qbits before it actually changes? In short, even if I can only see the result because of photon release, but I have my qbit reciever on Mars, and the transmitter on Earth, and each contains one half of the pair of entangled particles, why can I not transmit one bit of information from Earth to Mars before my qbit devices disentangle (because of that one bit I just sent), and then I see the photon after it leaves my local qbit. That would still be effectively instantaneous when you consider how long light / radio takes to get to Mars from Earth.

Perhaps you don't understand what entangled means?

Entangled in this context, scratt, doesn't mean that anything you do on Earth will have an effect on Mars (all it means is that measurement on Earth (given an entangled state) will let you know what they measure on Mars seemingly faster than light, but not really). In point of fact, unless you KNOW that the particles are entangled (which requires light speed communication of that information), you cannot say that you know anything about what has happened on Mars. That is, you need to know that the particles are entangled before any information is transmitted... the entanglement process is limited to the exchange of photons.

That is the entire problem with looking at entangled states as information transport -- you want to say that the information transfers instantaneously at the moment of measurement on earth, when in point of fact the photons that have allowed you to make that measurement and come to that conclusion, since you know that the states are entangled, have already had to exchange between Earth and Mars. Let me put it this way -- how do you know that your two particles are entangled unless you have measured that entanglement (which of course, is limited by photon exchange)?

A thought experiment:

scratt on Earth has the entanglement detector for particles A/B and a measurement device for the state of an atom A.
billybobsky on Mars has only a measurement device for the state of an atom B.

scratt measures that A and B are entangled, and measures the state of A, giving him the state of B on Mars.

billybobsky measures the state of atom B (which matches scratt's conclusion when he knows A and B are entangled) and knows nothing of atom A. In fact, while scratt may know what billybobsky knows some of the time, billybobsky doesn't know what scratt knows any of the time since he cannot detect entanglement.

Thus the detection of entanglement is a critical part of this knowledge...

[Kickaha]

... and therefore since the information that the particles *are* entangled must be transmitted no faster than the speed of light, and since the particle comprising one half of the entangled pair must itself be transported...

It's not what you think it is, scratt.

[Enki]

You gents are forgetting that if you entangle the pair and transport one of them, it remains entangled and you no longer have the pesky phone-home-and-cause/check-the-entanglement-before-you-can-read problem. Scratt isn't entirely wrong, the problem with the whole theory is when people think it will do anything meaningful for us here today.

There are quite a few experimental results where flipping the spin of entangled qbit Q also flips the spin on qbit Q' and the time it took to do so is far less than 1000x less than if the speed of light had been in play for transmitting the information. This is measured not by telling oserver' that something was changed and time to observe, both qbits were being "simultaneously" observed and Q was poked to flip it's spin. Q' flipped too, and the results were expected to take ~3ns at speed of light [1 meter separation] and the flip occured at sub-picosecond resolution. The time comparison was done "after the fact" and it could not be confirmed that the flips were correct until after the information time-cone expanded to the point that the we-poked-it information travel was made in accordance with normal lightspeed limits.

So what do I take away from that? If you aren't trying to do a two end comparison, and you constantly update your observations you should be able to pass information awful damn fast compared to the speed of light. Theorized to be instantaneous. Now the astute reader will say STOP! You cannot do an observation without destroying the entanglement of Q'. But unfortunately that has been found to no longer be the case. I say unfortunately as a colleague of mine has been toying with quantum cryptography and I ran across a paper he is very unhappy with. One that demonstrated how to "nudge" a qbit and read it without destroying it. That put man-in-the-middle attacks squarely back in play and is causing no end of angst amongst the cryptologists who aren't playing ostrich on this one. And if man-in-the-middle can work, arbitrarily quickly repeated observations can be made, I believe that shows we can pass information faster than current understanding of speed of light limitations allow.

I think the constraint of holding a set of qbits that were paired in physical proximity and constitute a fixed link pose problems that are far rougher on communications though. I think it is more likely we will discover how qbits work and take advantage of the mechanism directly long before we can get half of an entangled qbit pair halfway around the galaxy by transporting one starting today.