Quantum Telecloning Demonstrated?

An anonymous reader writes "According to Physorg eavesdropping on a quantum encrypted link can now be done without detection. From the article: 'The scientists have succeeded in making the first remote copies of beams of laser light, by combining quantum cloning with quantum teleportation into a single experimental step. Telecloning is more efficient than any combination of teleportation and local cloning because it relies on a new form of quantum entanglement - multipartite entanglement.' There is also a PDF of a related paper available here for background material."

I really dig this stuff...

but I'm starting to get discouraged now that the already hard to grasp concepts of quantum mechanics are being infused with new more complicated forms. In the end I just want to know if we can teleport ourselves cause I'm tired of my f'ing commute.

Re:I really dig this stuff...

I remember the good old days when unbreakable encryption would stay unbreakable for 15 years. Now it's being broken before it is even released.

It is not "encryption", it is "modulation"!

Encryption is a mathematical transformation. Quantym "encryption" has no mathematical transformation in it, it is just a way of modulating signals, i.e. a physical process! That is called "modulation" and has no security properties besides the physical signal properties. No mathematical proofs about this security can be given, since we still do not unterstand the physical universe completely!

Since all previous claims of security rested on not yet well understood physical principles, I am not surprised that once again claims of perfectness by ethically challenged researchers and businesspeople have turned out to be wrong.

Re:It is not "encryption", it is "modulation"!

No mathematical proofs about this security can be given, since we still do not unterstand the physical universe completely!

Perhaps you haven't read:

http://www.amazon.ca/exec/obidos/ASIN/0521635039/q id%3D1140401059/701-1812336-3224355 [amazon.ca]

I am not surprised that once again claims of perfectness by ethically challenged researchers and businesspeople have turned out to be wrong.

Perhaps you are not aware of a phrase that states "within current theory" that is implied everytime a theorist speaks. Or weren't you aware of that?

Or how about all those classical encryption schemes that were thought to be secure for long periods of time, but them turned out to be [near] trivial to break.

New attacks are created all the time. It doesn't mean the the researcher is ethically challenged. It just means that he thought he was right at the time, given the information at hand.

This is cutting edge research. Get a clue. Or at least your head out of your ass.

Re:It is not "encryption", it is "modulation"!

Wrong.
All the article claims is that the Evesdropper's location will be undetected. The fact that someone is attempting to eavesdrop will still be detected, and there are several well known proofs of security of this fact.
FTF Press Release
"Quantum cryptographic protocols are so secure that they can not only discover tapping but also where and how much information is leaking out. Now, using telecloning, the identity and location of the eavesdropper can be concealed."
Quantum cryptography is absolutely secure as long as the laws of quantum mechanics are true. And even if the laws of quantum mechanics are false, one can still do secure cryptography from some very weak assumptions (it follows from violating Bell's inequalities and no-signalling) see this [lanl.gov]

Re:It is not "encryption", it is "modulation"!

Disclaimer: IAAQIS (I Am A Quantum Information Scientist).

The parent poster (wwwrench) is completely, 100% correct. Is this really Slashdot, or did I type the wrong URL?

Seriously, though, the parent poster is bang-on. To elaborate a bit, quantum cryptography would be more informatively called quantum key distribution (although both names are common in practice). All it does is allow you to distribute a key for a one-time pad in a secure method, given that the laws of quantum mechanics are at least partially correct (one-time pads are information-theoretic secure, provided the key is not compromised or re-used). If somebody tries to eavesdrop, you can detect it, and respond accordingly. That response could be privacy amplification (if the information the eavesdropper gained was only partial), re-trying the protocol, or bombing the eavesdropper to smithereens. That last possibility is why quantum telecloning might be useful.

One other hitch is that quantum key distribution requires a small shared secret in order to authenticate the two parties trying to generate a key. Thus, quantum key distribution is not a complete replacement for public-key cryptography.

saw it coming

I knew this was gonna happen. I kept telling everyone it was just a matter of time.

ahh yes

so now we can listen in on quantum encrypted... wait a second... that doesn't exist yet.

O well, must be the FBI getting an early start.

Re:ahh yes

I think you're confusing quantum computing [wikipedia.org] (which is still mostly theoretical... the largest experimental proof has only involved a few qbits, and for all we know a full-fledged computer will be impractical) and quantum cryptography [wikipedia.org], which actually has been experimentally demonstrated.

Amazing as it may sound, researchers have used commercially available fiber-optics to send quantum encrypted signals. There are even companies that will sell devices, although right now the tech is not quite ready for prime-time. Still, it has been shown in a laboratory many times, and it's not fanciful to say that it may be deployed within our lifetimes (just depends on when the technology becomes affordable, compared to its benefits).

Also, as others have pointed out, this new result actually doesn't show that quantum crypto is breakable... it only shows that under some circustances the eveasdropper can remain anonymous... but the users of the channel will still know that it has been compromised, and will thus not use the keys that have been generated. That is, quantum crypto is still mathematically unbreakable when properly implemented (assuming that Quantum Mechanics is correct, that is).

Re:ahh yes

http://en.wikipedia.org/wiki/Quantum_entanglement [wikipedia.org]

If the composite system is in this state, it is impossible to attribute to either system A or system B a definite pure state. Instead, their states are superposed with one another. In this sense, the systems are "entangled".

Now suppose Alice is an observer for system A, and Bob is an observer for system B. If Alice performs the measurement A, there are two possible outcomes, occurring with equal probability:

      1. Alice measures 0, and the state of the system collapses to |0\rangle_A |1\rangle_B
      2. Alice measures 1, and the state of the system collapses to |1\rangle_A |0\rangle_B.

If the former occurs, any subsequent measurement of B performed by Bob always returns 1. If the latter occurs, Bob's measurement always returns 0. Thus, system B has been altered by Alice performing her measurement on system A., even if the systems A and B are spatially separated. This is the foundation of the EPR paradox [wikipedia.org].

The outcome of Alice's measurement is random. Alice cannot decide which state to collapse the composite system into, and therefore cannot transmit information to Bob by acting on her system. (There is a possible loophole: if Bob could make multiple duplicate copies of the state he receives, he could obtain information by collecting statistics. This loophole is closed by the no cloning theorem, which forbids the creation of duplicate states.) Causality is thus preserved, as claimed above.

http://en.wikipedia.org/wiki/No_cloning_theorem [wikipedia.org]

The no cloning theorem is a result of quantum mechanics which forbids the creation of identical copies of an arbitrary unknown quantum state. It was stated by Wootters, Zurek, and Dieks in 1982, and has profound implications in quantum computing and related fields.

Note that the state of one system can be identically entangled with the state of another system, such as by using a CNOT gate, but this does not constitute cloning since the systems will always yield the same value upon measurement. The no cloning theorem describes the inability to make separately measurable states.

What?

I was just gonna say that...

Seriously though, no matter how much I learn/study/pay tuition, there're always posts that make me realize how little I know about anything.

It's both humbling and inspiring.

Off topic, but someone had to say it... :)

Don't worry...

Don't worry. No matter how hard you try to know anything, you'll still be dead soon, in the cosmic scheme of things.

Have a nice day!

Heisenberg Uncertainty Principal?

What ramifications does this have on the heisenberg uncertainty principal? I may be no expert, but doesn't this mean that you could make a remote copy of a particle, and measure one's momentum and the other's position with great accuracy?

Re:Heisenberg Uncertainty Principal?

There is such a place, but the lesson plan is a nightmare.
Just as you think you know where your next lesson is you rush to get there to realise you've already missed it.

Finding out if the lecturers are still alive after opening the classroom door is an entirely different and wholey worrying scenario unto itself.

the cloning is only approximate

The reason that it doesn't violate the Heisenberg uncertainty principle is that the cloning is only approximate. You have one good photon, and you create two copies, neither of which are like the original. They are only somewhat like the original. This means that the evesdropper will get detected. Telecloning, just means that you clone the photon (approximately), and move it to another location (cloning+teleportation). The article claims that this means the location of the evesdropper will thus be safe, even if her attack is noticed. The article is actually about an experimental realisation of telecloning, not the discovery of telecloning itself.

Re:Heisenberg Uncertainty Principal?

What ramifications does this have on the Heisenberg uncertainty principle?

Obviously no one is quite sure.

Re:Heisenberg Uncertainty Principal?

Actually, if it could be done it wouldn't violate the Uncertainty Principle at all. A particle cannot have both a definite momentum and position, it can only have (roughly speaking) a probability distribution of each. So if you could clone a particle a zillion times, then each time you wouldn't get the same position, but rather if you looked at all of the clones together you'd get a distribution which would be identical to that of the original particle.

Having said that, cloning a particle perfectly is nonetheless forbidden by the No Cloning Theorem [wikipedia.org]. Basically (as I understand it) what this says is that there is an underlying principle of Quantum Mechanics that you can never know what position distribution a particle originally had, since the moment you measure it you focus it at that point and kill the original distribution. Cloning the particle would be a way of "cheating" that would let you get the distribution of the particle without destroying it, so it ends up being forbidden.

Now, even though you cannot perfectly clone a particle, you can imperfectly clone it, which is what these guys have claimed to have done. If you look at the abstract, you will note that they are only claiming a fidelity of 58% +/- 1%. (The theoretical limit is five-sixths (83%) according to this article in New Scientist [newscientist.com].)

A non-perfect fidelity, however, isn't so bad. Alice and Bob probably can't get their own optimal fidelity when using Quantum Cryptography anyways; in theory they should expect to see 50% of the bits get through, and then worry if they see it goes down below that -- even, say, to 49%. In practice, their equipment might only be able to get 40% of the bits through, and sometimes even less than that, so they'll tolerate lower rates than 50% since they are figuring that eavesdropping would lower this rate all the way down to 25%, and that is something that they'd surely notice. However, by using the techniques like those discussed in the article you can apparently eavesdrop less than perfectly in a way that, while still lowering the bit transmission, does not make it as bad as 25%. Thus, if Alice and Bob were naive they'd just assume that their equipment was faulty and not that there was an eavesdropper.

So the moral of this story is that from now on Alice and Bob will have to make their apparatus work much more reliably so that they can expect a success rate of say, 45-50% rather than 35-50%, and thus be more likely to notice a slight degradation in the signal due to an eavesdropper.

Quantum Transmission

It's always bugged me that they call it quantum encryption since it's really classical encryption used in a quantum transmission role. I don't see anything "quantum" about the encryption itself. Of course, it probably sounds cooler that way...

Another basic law of physics...

If someone says something, someone might overhear it.

I just made that up, but the obvious corollary is this; If you don't want something to be known, don't say it!

Thank you very much, I'll be here all week. (Mostly because I have nowhere else to go.)

Can I get this in English?

Most of the time, I at least read TFA and make a dumb comment. This time, I read TFA and just felt dumb.

Can some explain it and use real-world examples?

As a physics major...

As a physics major who has taken the time to look over the paper (read: barely skimmed--I am a lazy college student afterall), I would just like to offer my sincere opinion of "HUh?"

I hope that will be helpful to other Slashdotters outside the field.

uh-huh

I love it when they come up with these totally original and ambiguous names like "mutlipartite entanglement." Why!? What EVER could that mean? Oh brother...

Quantum Encryption

Hacked before it was even released.
That is worse than the Xbox.

I remember reading about this undefeatable encryption on slashdot a few months ago.
Seriously, that had to be the most short-lived security scheme ever.

This is great

Now I can be screwed in 32 different states. Kinda like Madonna.

right...

Back to IP over avian carrier? :)

smash.

Cloning is immoral!

We need to put a stop to this quantum cloning. It is immoral and wrong. Who knows where it might lead!

Great!

Just great. Now we can hack a form of encrypted transmission we don't even have yet...

Hmm, how seredipitous...

It's interesting that we were just talking about this very article (well the actual release, not this article about it) in a analytical mechanics class I'm taking. One of the things that wasn't mentioned in this article was the fact that the beam of light cloned was only done so to about 66% accuracy. I'm sort of kept from going into more details about this by my own fairly limited grasp on the matrix mechanics, but as the clone wasn't perfect, the uncertainty principle was upheld. It is fairly worrisome to see this study spun much out of proportion though. The opening blurb about Captain Kirk only reinforces untrue stereotypes about the potential of quantum teleportation. Alas, if journalists were physicists...

Not without detection?

According to the article: "Quantum cryptographic protocols are so secure that they can not only discover tapping but also where and how much information is leaking out. Now, using telecloning, the identity and location of the eavesdropper can be concealed." Does this mean the eavesdropping can still be detected, but no information about the eavesdropper can be obtained?

Dammit

I just finished compiling Quantum encryption support last week, now I'll have to recompile my kernel. Any word on when the patch will be released? Which repository should I use?

no fundamental rules of QM broken

I haven't read the PRL, but the linked article says:
"Quantum cryptographic protocols are so secure that they can not only discover tapping but also where and how much information is leaking out. Now, using telecloning, the identity and location of the eavesdropper can be concealed."
So as far as I can tell, the parties sending and receiving the message still know that their is an eavesdropper, just not
"their identity and location." I am sure that heisenberg is still fine, a quantum state still cannot be cloned, and information cannot be sent faster than the speed of light. If this was the case, this would be the headline, and I'm guessing it would be on cnn headline news. (Maybe the world isn't that nerdy though... ;-))

Other news

So let me get this straight

There is a security hole in technology that hasn't even been developed yet?
Isn't someone gonna put a patch out for it?

I have a long distance quantuum eavesdropper

On average, I'm able to correctly decode 50% of the bits.

Quantum Encryption

This article is NOT about quantum cryptography at all. Telecloning is related to quantum entanglement which is behind basic quantum cryptology, but they are two completely different subjects. Also, we don't even have basic quantum computers yet...I think it will be a long time before we're teleporting people.

ScuttleMonkey didn't read TFA, clearly...

The submission is simply wrong: the article says

"Quantum cryptographic protocols are so secure that they can not only discover tapping but also where and how much information is leaking out. Now, using telecloning, the identity and location of the eavesdropper can be concealed."

, but the summary says "eavesdropping on a quantum encrypted link can now be done without detection", which is exactly the opposite.

Calvin's work?

Are we sure that this story wasn't posted by Calvin as his latest school assignment? If you have a look at the PDF with edits left in, you'll see words like "Transmogrify" crossed out all through it. I'm sure Hobbes could have put him up to it.

Quick summary of quantum theory

Theorizing that one could time travel within his own lifetime, Dr. Sam Beckett stepped into the Quantum Leap accelerator and vanished .... He woke to find himself trapped in the past, facing mirror images that were not his own and driven by an unknown force to change history for the better. His only guide on this journey is Al, an observer from his own time, who appears in the form of a hologram that only Sam can see and hear. And so Dr. Beckett finds himself leaping from life to life, striving to put right what once went wrong and hoping each time that his next leap will be the leap home.

"Oh boy.."

IIRC

That reminds me of the Windows XP anticopy scheme. Long before it was even released publicly, the crack had already hit the street. Sweet.

Ah, yes!

I've been quantum telecloning via multipartite entanglement for years with my ultra-flux quasi capacitordangle jimmy-rigged to a quanto-farscope for multi-resolution ohmage. I built this with the latest in Lego technology!

Missing the point

It's a quantum party line!

A word about quantum telecloning

From the paper referenced in this PRL, Physical Review A 59 (1999), M. Murau, D. Jonathan, M.B. Plenio, V. Vendral:

"In this paper, we investigate the following scenario. Alice holds an unknown one-qubit quantum state |Phi> and wishes to transmit identical copies of it to M associates (Bob, Claire, etc.). OF COURSE, THE QUANTUM NO-CLONING THEOREM IMPLIES THAT THESE COPIES CANNOT BE PERFECT. The best Alice can do is to send optimal quantum clones of her state (the most faithful copies allowed by quantum mechanics), which we assume to be sufficient for her purposes." (Caps are mine.)

Now I admit, the PRL is too dense for me to understand, but based on this, it lookse to me like perfect quantum clones are not allowed. In fact, this quantum no-cloning theorem follows quite directly and naturally from first principles. We won't be cloning Kirk anytime soon, at least not perfectly.

huh?

hmm... what I'd like to see on the web is an introduction to quantum physics for non physicists. something that outlines the primary results of quantum physics with some graphical explanation for laymen.

most people with an interest in physics, whether they be physics majors who have taken modern physics classes or not, have some intuitive ideas about what relativistic physics means. however, when it comes to quantum physics, people just think "black magic happens here"...

what's worse is that people increasing will say "quantum physics" and do a bunch of handwaving to promote psuedoscience. people don't do this with relativistic physics because most people at least understands the *domain* of relativity and know that it isn't likely to lead to inventions that say, clean your clothes better, or something along those lines. quantum physics on the other hand is sometimes quoted when selling just such products (I've seen little plastic balls that are supposed to go in washing machine along these lines) because most people just don't know what the results of quantum physics are, just that they are supposed to be powerful and profound, so charlatans play on that uncertainty.

and... anyway I think we all agree that the *public* understanding of scientific issues, on a least a basic level, is really important to the health of our society. I'm sure we can all name a couple of other issues where poor understanding of science in the public sphere and in government has led to poor decisions and general idiocy. popularization of science and science understanding seems like a goal we should be devoting more resources to.

Ultimate broadband?

The scientists have succeeded in making the first remote copies of beams of laser light, by combining quantum cloning with quantum teleportation into a single experimental step. Telecloning is more efficient than any combination of teleportation and local cloning because it relies on a new form of quantum entanglement - multipartite entanglement.'

Maybe I'm missing the point here (because I'm not a theoretical physicist), but what would happen if you combined something like this (light cloning) with fiber optics (data transfer) over long distances? Would it do away with having to have tons of underground fiber? Would it create an exponential jump in bandwidth?

Just food for thought. :)

Totally silly, fixable with $1500 tool

Ahem, the authors may know a lot about quantum stuff, but they don't know anything about how fiber optics work.

If somebody is tapping the line, strongly enough to intercept photons, it's easily determined by using a TDR (time-domain reflectometer)-- basically optical radar. Even a 1% discontinuity in amplitude or length can be detected. All it takes is a little handheld gadget.

AND if they're tapping and resending the signal, it's lost all its entangled properties, so the other end won't get the right combination os states, proof there's tapping going on.

Original press release.

I wish people would look up the original press release instead of advertising the physorg tarpit.

Here. [york.ac.uk]

(yes, all the stupid "teleportation" stuff was in the original)

Excuse me?

Um, I know I got Doom 3 pretty late and have been playing late into the night but...is this a real news item?

Have we now moved into an era in which even NON-EXISTENT technology is already being OBSOLETED before it becomes real?

This just in: hydrogen fuel is officially obsolete; dilithium crystal is the fuel of the future

Oh boy

You what that means...

made by humans, broken by humans

nothing new...

I Think, Therefore It Is!

a new form of quantum entanglement - multipartite entanglement

Because I'm pedantic, I'd like to log a clarification to this. It's not a new form of quantum entanglement. It's presumably been around since the beginning of time. What it is is a newly discovered form of quantum entanglement. This is not a case where human thoughts created something. You are not a figment of my imagination.

Re:What it all really means

DAMMIT! Now I have encrypt my files all over again!
Hopefully that Quantum Pretangle Cloning will stay unscannable.

Re:What it all really means

I'll feed the troll..

Feasibly, someone that had access to the cables could cut them, put a receiver, a transmitter, and a computer that receives, records and retransmits everything in and splice everything up properly when done- aside from a temporary and puzzling outage- no one would be the wiser.

It can be determined from reflectometry exactly where the break is, and someone would go out and check the cable eventually with an ROV or something and find the splice, but I'd imagine for a while you could have a tap in place as long as the interruption was minimal.

Around here, when there's a fiber cut, it takes hours- but I assume some of that is discovering the cut, finding a crew and getting to the site. I would suppose if you put one of the worlds top splicers right there that the interruption could be made fast enough that the techs monitoring the connection would be confused but would chalk it up to some sort of temporary bend or other error.

I am not a fiber tech, but all of that seems fairly reasonable to me.

In other words, I don't think quantum teleportation is necessary or even applicable to straight forward fiber implementations that don't depend on the orientation of photons.