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back to article 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 …

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Joke

I'm impressed!

Or I'm not...

Where's the cat?

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Happy

Re: I'm impressed!

The cat? It's here and there...

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Anonymous Coward

Re: I'm impressed!

For some reason the Tom Lehrer song "I Got It From Agnes" came to mind when read about this. WHere are the singing mathematicians when you need one?

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I *think* I understand how this works ...

... but the terminology & bra-ket notation gives me a headache :-)

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Holmes

Re: I *think* I understand how this works ...

Don't be fazed, it's just a scalar product with fancy greek letters. All is linear algebra ... which is a hint that something may be missing, natch.

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Flame

Not Fair

I've been a bit annoyed by the way that Alice and Bob have been getting lots of interesting work over the years. Now, they've been sent to do interesting work in the Canary Islands !

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Anonymous Coward

Re: Not Fair

I had a bit of a fling with that Alice once and Bob found out about it straight away –even though he was miles away, at the time.

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jai
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Re: Not Fair

it's Zed that I feel sorry for. Poor bugger hardly ever gets any work at all.

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Happy

Re: Not Fair

"it's Zed that I feel sorry for. Poor bugger hardly ever gets any work at all."

That's because Zed's dead, baby.

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Alien

Ok, perhaps I am being dumb...

...but how do they know that the received photon is actually the one they sent and not just one that looks like it (or that the characteristics of the photon exhibiting similar behaviour are not just a coincidence)? Sceptical? Me?

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Re: Ok, perhaps I am being dumb...

"Sceptical?"

You Sir must be an Engineer - or went to the same school as I where they taught "question everything"

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Joke

Re: Ok, perhaps I am being dumb...

It has "The One" written on it.

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Pirate

Re: Ok, perhaps I am being dumb...

maybe Eve fiddled with it.

Sadly while extremely wonderful research it's never going to lead to an Ansible. Actually the article doesn't explain why this would be better than existing communications systems.

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Re: Ok, perhaps I am being dumb...

AFAIK at the quantum level if the photon received 'looks' like the photon transmitted (it has the same quantum state), it is in fact the transmitted photon.

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Re: Ok, perhaps I am being dumb...

So photons have a kind of GUID attached to them? No none of this quantum leap stuff makes sense. If I were in charge I would demand we go back to using the pigeons.

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Go

Re: Ok, perhaps I am being dumb...

I thought the article explained quite well that it's not limited by that pesky "speed of light" thing Einstien kept going on about.

What it failed to do was beat you over the head with it.

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Headmaster

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.

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Re: Nein, Nein, Nein!!

> Correlation in the measurement of a shared state does, however, not need information transmission.

What about correlation in a change of state over a distance? Alice & Bob's cards don't change state together once allocated. AIUI entangled photons can.

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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.

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Holmes

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!)

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Anonymous Coward

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.

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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?

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Paris Hilton

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.

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@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 :(

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Boffin

Correct

It's all about encryption, or rather making comms secure from evesdroppers. If someone intercepts the communication then the transmission is lost. It's the holy grail in secure comms.

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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.

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synchronise time

That's bloody impressive! How does that work exactly? Is it a timey wimey connection?

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Re: synchronise time

Both use a pulse from the same very distant stellar source. Is that why those stars exist? Convenient Galactic Navigation beacons and clock synchronisers?

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Encryption

The use of Alice and Bob suggests the reason behind this experiment isn't to develop an Ansible, but make communications more secure (at the same speed).

I'm sure Eve is watching with interest.

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g e
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Happy

Can the next pair please be named

Wheatley and GladOS in homage to Portal, please?

Space. SpaceSpaceSpace. Spaaaace. Space.

I thank you.

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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.....

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Re: Instant means instant

Not so, I'm afraid. The effect is thought to travel instantaneously, but can't be used to transmit information, other than randomness.

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Re: Instant means instant

You can't have real-world (non-quantum) information transferred FTL. Quantum state alone doesn't help. Hence, the second link in the experiment.

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Lottery

My quantum lottery card is purchased, I will be checking my numbers to make them win come weekend.

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What's the El Reg unit of bandwidth?

"The weather, they note, delayed the experiment for a year."

So perhaps the most awesome thing about this experiment is that it gave us a real-world opportunity to use the word "nanobaud".

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Unhappy

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.

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Headmaster

> In quantum teleportation, the phenomenon known as “entanglement” to transmit information instantaneously.

This sentence no verb.

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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.

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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.

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I've just one word for all this

Headache.

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Paris Hilton

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.

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