Austrian Physicists 'Teleport' Light Over 600m

openSoar writes "The BBC is reporting that: 'Physicists have carried out successful teleportation with particles of light over a distance of 600m across the River Danube in Austria. When physicists say 'teleportation', they are describing the transfer of key properties from one particle to another without a physical link.'"

Comments

Story title and summary all wrong

[menscher]

Ok, as a physicist I initially thought these must be crackpots. A careful read made it clear that the science is good, it's just the slashdot title and summary that don't make sense.

What they did NOT do is teleport particles of light. That just makes no sense. Light was used as the means of conveying the information used to teleport the quantum properties from one particle to another, without the particle having to travel.

By the way, the reason this is called "teleportation" is that the particle effectively travels at the speed of light -- its properties can be transferred by light. If this could be applied to humans, for example, it would allow for light-speed travel, without all the nuisances of acceleration. It should be noted that this does NOT violate the universal speed limit.

Oh, and before someone asks, this is entirely different from quantum tunnelling....

Re:Story title and summary all wrong

[Anonymous Coward]

Well, if you simultaneously transferred the _properties_ of every atom in your body to some atoms elsewhere, then you would have achieved teleportation of your body. The fact that your actual subatomic particles didn't move makes it seem kind of like "fake" teleportation, but in the strange quantum world we live in it is completely equivalent to and indistinguishable from "real" teleportation (whatever that means). That's why they call it teleportation even though the actual particles involved don't physically swap places. Of course, usable teleportation of everyday objects is infeasable because in order to get the same object out at the destination you need to have a supply of all the types of atoms in the original object plus the means to assemble them in the configuration of the original object.

Basically you need to replicate the item first (roughly, ignoring the quantum states of the particles), then you can transfer its quantum state using quantum teleportation to complete the teleport. But you have to do every atom in the object at (about) the same time to avoid having the teleport process affect the object too much. The bandwidth needed to transfer the information held in even a small object dwarfs even theoretical limits on proposed futuristic communication channels. And assembling the replica in the first place is probably even harder; and if you've already made an almost perfect replica of the item then who needs the original anyway? Once you have replicator technology, teleporter technology seems less useful. (You might think it would still be useful for teleporting humans, but if we could do that it would imply that we could also replicate humans. Think of the consequences of that...)

Wow, that ended up a lot longer than I intended. Some physicist person please come correct all the errors I probably made ;-)

There was a physical link..

[kyhwana]

Err, there was a fibre link, ie a physical link. RTFA submitter?

Re:There was a physical link..

[Rolken]

Um, I'm not even entirely sure what you're getting at... but the point is, two photons are entangled, you move one far away, then mess with the first one and the second one instantly changes in the same way. The photons don't teleport, but their information does.

I was going to ask a dumb question, but...

[benjamindees]

I decided to do a little googling instead:
How this relates to quantum computing:
When a single photon is split by a beam splitter, its two `halves' can entangle two distant atoms into an EPR pair.

How to entangle a photon pair: There are certain nonlinear (BBO) crystals, such as are used in optical parametric oscillators, that will supply entangles photon pairs.

Re:Does anyone have a handy definition of teleport

[Boronx]

Could the article have it wrong? Perhaps they misunderstood the scientists. The photons move at the speed of light, but the entanglement effect ought to be instantaneous since from one way of thinking the distant photon was already in the same state as the input photon.

Instant travel

[laughing_badger]

One interesting point to note is that, if it were possible to transport a person via this process, the trip would appear to be instantaneous. Although travel would occur at the speed of light, no time would appear to pass for the traveller. Cool.

Re:If this works long distance...

[FooAtWFU]

If you read either the article or existing comments you'd notice that this process is limited by the speed of light. The latency is still there with this system. Removing it would be wonderful, yes, but this will not do it. Nothing currently known to physics will. Nothing currently known to be knowable by physics will. And precious little thought to be possibly knowable by physics will either.

What is really happening

[jgardn]

It's really more than that, because you have to remember that each photon is neither fully in one state or the other. It is a combination of the two. This is "quantum superposition", or the concept that a particle is really a manifestation of discrete possibilities.

I think a good example of what is really happening is to imagine a pair of dice guaranteed by nature always to roll a 7. If you see a "3" on one die, then there absolutely must be a "4" on the other. Anything else would be a violation of several fundamental laws. Now imagine taking the two dice and seperating them by a large distance, and then rolling one of the dice. Even though there is a large distance, and even though the speed of light is the limit at which information may be sent, the other die will show the other number pair when measured. (Debate about whether one measurement happens before another is meaningless due to special relativity. In other words, one measurement cannot cause another to be so.) So if you roll a 3, the other die will roll (or has rolled) a 4. If you happen to roll a 1, then the other die will roll (has rolled) a 6. Spooky, huh? Welcome to the crazy world of quantum mechanics! Just when you thought you understood it all, nature throws a curveball.

Now your first instinct is that somehow those dice decided on something befor they were seperated. This is not how quantum mechanics works. The two particles can't "decide" on anything until measurement. Every observation and every calculation tells you that the particles did not decide on a specific state beforehand. I could show you why this is so, but it's pretty complicated and involves higher level mathematics than the average slashdot reader can understand. If you're really interested, I suggest reading a QM textbook. They keep this topic in one of the last chapters, so you have a lot of studying ahead of you.

Finally, your next reaction is going to be, "Wow, we can communicate at speeds faster than the speed of light!" Unfortunately, the way this works you can't "force" the particle to a particular state. If the particle comes in with a preference for one state or the other, then the complement will be true for the other particle. (By preference, I mean the chance of one state is 90%, and the other is 10%, or 99.99% and 0.01%, not something pre-decided. See the above paragraph.) And thanks to special relativity, it is fruitless to try and decide whether one measurement occured before or after another, so a causality link cannot be established.