I'm impressed!
Or I'm not...
Where's the cat?
Canary Islands host long-distance quantum teleportation
The Canary Islands of La Palma and Tenerife have been briefly connected by a quantum teleportation system that sets a new distance record for the spooky communications technique. In an angle that will get Trekkie bloggers reaching for the “beam me up” metaphors, the researchers, from Austria, Germany, Canada and Norway, hope …
-
-
-
This post has been deleted by its author
-
-
Wednesday 23rd May 2012 07:33 GMT Destroy All Monsters
Nein, Nein, Nein!!
1) We have a typo, commander! It's "Einstein", not "Einsten".
2) "to transmit information instantaneously"
Not so. Information is always transmitted at "c" in the best of cases. Correlation in the measurement of a shared state does, however, not need information transmission. Consider a black card and a red card. If Alice and Bob each have one, and Alice checks the color of her card, how much time did it take for Bob's card to take on the other color? Exactly. If quantum, the colors are not even fixed before at least one side is measured (which makes things interesting as either Alice or Bob can measure first depending on the reference frame) but you get the idea.
Still, this is good engineering stuff.
-
Wednesday 23rd May 2012 09:55 GMT Brewster's Angle Grinder
Re: Nein, Nein, Nein!! (@Destroy)
Your card analogy only describes hidden variables. Here's a (hopefully more accurate) analogy:
Imagine a server that generates pairs of 1 pixel images, each a mix of red and green. It sends one of the pair to your lab in Tenerife and one to your colleague in La Palma. You and your colleague examine your pixels, but only in the red or the green channel and use that to classify the image as 'red' or 'green'. Your colleague emails you his results, and you compare notes.
What you find is where you and your colleague have examined different channels, there is no correlation in colours; they coincide only as often as you'd expect by chance. But if you chose the same channel, then there is a correlation, and you get the same colour more often than chance alone; it's as if the server "knew" in advance, when you and your colleague would examine the same channel.
The above is just the Bell inequality, and still misses its full subtlety. Quantum Teleporation (as I follow it) uses this process to transfer some information in secret. It still depends on the pair of you comparing notes. But if someone intercepts those notes, then they don't contain the all the information. As some is transferred in the entangled qubit.
-
Wednesday 23rd May 2012 12:31 GMT Destroy All Monsters
Yes ... and no
"Knowledge of things happening in advance" is not the correct metaphor to apply. You just need a judicious extension of probability theory:
http://www.mth.kcl.ac.uk/~streater/lostcauses.html#I
http://www.mth.kcl.ac.uk/~streater/probably.html
I won't add a boffin icon because I'm unfortunately not too well in the saddle in all this. Hopefully I will be at some future time... (as if!)
-
-
-
Wednesday 23rd May 2012 08:51 GMT Anonymous Coward
Re: Where's the teleportation?
I believe it’s the Information that's being teleported not the photon.
Two photons are 'entangled' (and presumably have to be together to do that). One of the photons is then sent away via the fibre.
The state of a third photon is then transferred onto the first and because the first and second photons are entangled the second photon then immediately has the same state as the first. The information effectively teleported.
I guess this means that it’s possible to move information between two points without any possibility of it being monitored because the is no channel to snoop on between the two points. What I would like to know is do the two photons remain entangled after the teleportation event has happened or is it a one shot deal?
-
Wednesday 23rd May 2012 10:20 GMT Displacement Activity
@AC: Re: Where's the teleportation?
You're mostly right.The transfer doesn't happen like this, though. The actual information transfer happens by sending data bits on a classical comms channel, at or less than the speed of light. Effects due to entanglement do travel instantaneously (I think this has been experimentally shown to be at least several thousand times faster than c), but you can't transmit information at this speed. See my other reply for the actual mechanism.
And yes, the point is to prevent snooping, and yes, it's a one-shot deal. The measurements destroy the original entanglement. Back to C++ now :(
-
-
Wednesday 23rd May 2012 10:08 GMT Displacement Activity
Re: Where's the teleportation?
> I don't know if I'm missing something, but sending a photon through a fibre doesn't seem like teleportation.
It isn't. The 'teleportation' is the transfer of quantum information (a 'qubit') from location A to location B. There are complex reasons why this can't be done classically (ie. putting it in a box and carrying it, and so on), but there's a work-around. The work-around requires Alice to measure two quantum states, and send the results of her measurement as two classical bits on a classical comms channel (a satellite link, maybe) to Bob. Bob then uses these two classical bits, together with his half of the entangled pair, to regenerate the qubit that Alice wanted to send to him. The entanglement is destroyed in the process, but Bob ends up with something that has the quantum state that Alice wanted to send him. Voila, teleportation. Sort of.
-
Wednesday 23rd May 2012 14:03 GMT Dan 10
Re: Where's the teleportation?
The way I read it, the entangled photon pair (of which one half was sent over the fibre) merely acts as the baseline. It was sent merely in order to create distance between points A and B. The teleport bit was when a third photon was injected into one half of the entangled pair (at point A) and the OTHER half of the pair (at point B) reflected the changed state immediately - from oodles of km away.
Impressive stuff, my brain hurts trying to imagine how the teleport itself actually takes place.
-
-
-
Wednesday 23rd May 2012 09:11 GMT Great Bu
Instant means instant
The reason Einstein didn't like quantum entanglement is precisely because it does allow for information transfer at higher than the speed of light. If you create two photons in a particular way* they are 'entangled' - whatever happens to one, the opposite immediately happens to the other (again simplyfying but if you turn one to the left, the other immediately turns to the right). This change of state on the second entagled photon happens literally immediately and regardless of the distance between the two photons in the entangled pair (the theory, and all experimental evidence so far, stretches to suggest that this is the case even on opposite sides of the universe**).
This means if you can maintain the entanglement whilst you transfer one of the entangled photons to a distant place (which is the hard part, as alluded to by the difficulty mentioned with regards to 143km of air) then you can use this link to transfer information with no delay at all. OK, the transfer of the original photon to the distant receiving location occurs at the speed of light but once it has arrived, further endless information can be sent instantaneously as long as the entaglemet can be maintained (like laying a transatlantic cable, the cable laying goes at the speed of ship but the phone conversations subsequently go at the speed of light (ish)).
You know you have the right photon at the receiver end when you find the one that is carrying your test signal.
This means not only an ultra-secure communication (there is no known way to intercept the 'entaglement signal') but also entirely delay-free (which is nice on a planet but really useful interplanetarily or even interstellarly).
*massive simplification but the method is not really relevant to my point.
** I know, no such opposite sides exist.....
-
Wednesday 23rd May 2012 12:57 GMT Bush_rat
Shame...
Quantum is science that's gonna take me a while to wrap my poor frazzled head around. It might not be as complex as I think, but when I hear things like "two places at once" or "teleportation" used with the word "Quantum", every thing I thought I knew about science is questioned. I just trust the prof to know what he's doing.
Besides, isn't questioning science what science is all about.
-
Wednesday 23rd May 2012 15:28 GMT Yet Another Anonymous coward
Not sure I see the point
I get the whole collapse wave-function action at a distance bit (went to physics, got the T-shirt)
But I don't see how this provides any security?
If Carol was in the middle with an identical model Quantum Communicator 3000 she could grab the first entangled photon. Then create and send a new uncollapsed one onto Bob with her own message.
The only way Alice knows that it was Bob that collapsed her photon and not Carol is the common time reference and it seems that this would be just as reliable (if not more so) for a regular communications packet going down a fibre.
-
Wednesday 23rd May 2012 17:34 GMT Bounty
Re: Not sure I see the point
"If Carol was in the middle with an identical model Quantum Communicator 3000 she could grab the first entangled photon. "
--------------------------------------------------------
"quantum mechanics guarantees that measuring quantum data disturbs that data; this can be used to detect an adversary's interference with a message"
- http://en.wikipedia.org/wiki/Quantum_cryptography
Basically Carol couldn't pass on a photon that isn't obviously modified.
-
-
Thursday 24th May 2012 15:45 GMT Gobhicks
All very interesting...
... but (off topic, but not completely): while we are diligently surveying Universe with all kinds of instruments at all kinds of wavelengths, are we systematically collapsing the Cosmic Wave Function towards one out its many potential states, and when this process is complete, will cats inherit whatever remains?
Paris, cuz you know she thinks about this stuff all the time.
This topic is closed for new posts.
Biting the hand that feeds IT
