The Viterbi Algorithm and Quantum Communications 91
eldavojohn writes "There have been a lot of tests in using quantum mechanics to communicate across large distances. But a student & a professor at USC have proven that the Viterbi algorithm can be applied to quantum communication. In the traditional Alice sends Bob a message scenario, 'Bob can reliably spot errors, and knows which message qubits are bogus before he opens the message — crucial, because opening it destroys it; and if it is garbled, he has nothing.'"
Alice (Score:3, Funny)
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Spoken like a true married man.
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Re:Alice (Score:5, Funny)
And for that matter what is the chance Alice will just say it once?
Go ask Alice. I think she'll know.
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Go ask Alice. I think she'll know.
Well, we are talking about QM, where logic and proportion do indeed fall sloppily dead...
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She just spouts off a bunch of nonsense about a dormouse and "Feed your head". Damn hippies. You wouldn't need quantum theory to understand a true red blooded American!
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When Eve isn't listening (Score:1, Interesting)
> So . . . when is ANYTHING Alice says not garbled?
Whenever Eve isn't listening. Of course, given that our government is spying on everyone, you're right. You can simply DoS the connection by spying on them all the time.
Crap, did I just break quantum encryption?
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Re:Alice (Score:4, Funny)
She's the chick that Bob is seeing behind Eve's back, if I understand the situation correctly.
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You're all going to die down here.
Alice 3 Bob (Score:5, Funny)
Re:Alice 3 Bob (Score:5, Funny)
Everybody knows they have the hots for one another.
Kids these days. When will they learn that its not worth the risk. Safe encryption should be practised all the time, not just when you feel like it.
Entangling... (Score:5, Funny)
So you're suggesting Bob and Alice get entangled? That's spooky... too bad we wouldn't be able to watch.
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Re:Alice 3 Bob (Score:4, Funny)
oh crap, now you had to upgrade Schroodinger's cat to a fetus
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Mayeb they could do it in a super position ? Har! har! har!
Alice? (Score:4, Funny)
Who the ---- is Alice?
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It's a placeholder name, like a variable named "foo"
See http://en.wikipedia.org/wiki/Alice_and_Bob [wikipedia.org]
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Right. Gompie.
[...]"It spawned a more risqué version in 1995 by the Dutch band Gompie, titled "Alice, Who the Fuck is Alice?". "
http://en.wikipedia.org/wiki/Living_Next_Door_to_Alice [wikipedia.org]
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And here I assumed it was from Bob and Carole and Ted and Alice......Bob was married to Carole. Ted was married to Alice. But part of the plot was for Bob and Alice to get together......
Layne
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She's friends with Lena and, inexplicably, a teapot.
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Re:Alice? (Score:4, Funny)
You can get anything you want at her restaurant, I know that much.
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'Cepting Alice, of course.
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I got a whole bunch of color glossy photos with circles and arrows and a paragraph on the back of each one that says otherwise.
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You can tell all the people with mod points are too young to know the song. They should be fined $50 dollars and have to pick up the garbage in the snow. :-)
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Alice is the girl Bob is cheating on his wife Eve with.
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Similar to a metasyntactic variable [catb.org], such as foo/bar/baz...
Alice and Bob [catb.org] serve as the archetype personalities in cryptographic communication examples.
Ignorant Post (Score:2)
So as long as he doesn't open it, it might be garbled, or maybe not. Isn't the fucking cat is dead at that point?
I assume there has to be some sort of value in this discovery, but neither the summary or article seem to do a great job of expressing it.
I thought the problem with quantum mechanics was in measurement, not knowing something is bad before you measure it.
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The value in this is that with these entangled photon's we can transmit data across any distance instantaneously. From here to anywhere in the universe.
No, you cant. It would violate relativity and causality.
These quantum communication systems require a classical communication channel, which is restricted to the speed of light.
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What would happen to the spinning of one particle if it was the subject to massive time dilation from either being close to the speed of light or within the event horizon of a black hole?
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At this point. Who knows what we may figure out in time?
Look where we were 100 years ago. 200 years ago. 300. Do you get what I'm hinting at?
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Yes. You're hinting that you didn't take any quantum mechanics classes.
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This is true. But my point being is that we only know that we do not know everything, we don't know how much we don't know. We've made so many advancements recently, so many that I would not rule out more advancements with quantum theory.
Perhaps not having an "inside" knowledge of the theory allows me to see it abstractly - as any other science.
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What!? Troll!?
Er.. I hope that was a mistake?
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Describe a one time pad. The channel transmits true statistical randomness, which is the exact opposite of information.
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The basics of entanglement are thus: Person A produces an entangled pair of particles. He se
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No, you cant. It would violate relativity and causality. These quantum communication systems require a classical communication channel, which is restricted to the speed of light.
Actually, you are wrong, since the communication occurs along the entaglement linkage, which is in a higher order dimension than space-time, which dimension it is all depends on which version of M-theory you currently ascibe to.
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No, it would violate your perception of relativity and causality.
It is quite possible that the information could follow a pathway that actually does go all the way across the universe, but if it's at the correct angle it really doesn't take much, if any, time relative to the position on either end.
Stupid humans, still thinking that time is somehow different from distance.
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The cat may or may not be dead, but if you wait long enough to open the box, it'll starve anyways.
This is for deriving information from Markov sets (Score:5, Informative)
For those wondering what use this has.
Say you had.... a buttload of code, and wanted to find the context free grammar for the language. You could use a Viterbi algorithm to pull out a statistically likely parse tree (the Viterbi Parse). The thing you're pulling from is often called a Markov process which is a model for the evolution of a state changing, memoryless system. So, over time, you can retrieve a grammar from a running process.
How this applies to QM is left as an exercise to the reader (5 stars, unless you're Don K His-self, in which case it's 2).
ianaqp
Re:This is for deriving information from Markov se (Score:5, Funny)
And for those of you wondering...
Markov was Chekov's evil twin on Star Trek.
Re:This is for deriving information from Markov se (Score:3, Informative)
Just one nit to pick.
Generally, we are talking about hidden markov models. linky [wikipedia.org]
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You are of course, correct.
But.... that's the only nit? I shall declare this a win then. :)
Thanks
Re:This is for deriving information from Markov se (Score:2)
Say you had.... a buttload of code
And the imagination of slashdotters keeps on bewildering me! I salute you sir!
Re:This is for deriving information from Markov se (Score:2)
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How much is a buttload as expressed in Metric Fucktons? I only deal in Metric.
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Depends on whether we're talking standard buttloads or metric buttloads. The standard buttload is generally measured in Rosanne Barr's. So we assume the standard 250 KLOC per buttcheek. However, the metric buttload is a moving target since, much as the yuan is pegged to the American fiat peso, the MB is pegged to Oprah Winfrey.
In short, since the current rate between between the Winfrey and the Barr is roughly 1:1, you can safely assume them to be equal. Tomorrow however, I hear that Oprah will be dining
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This could be huge (Score:5, Interesting)
I'm not smart enough to figure out the details of what they've done, but it sounds like really promising work. "Communication" is perhaps too narrow a term for the applications, though.
A big part of the problem with building quantum computers right now is keeping the qubits stable. The real world is constantly trying to "observe" (or interfere with) the qubits. When that happens, your quantum states break down and you lose your computation. This is a bit reason why we've only been able to build small (5-qubit) machines: it's very hard to keep things isolated and stable.
If you have a practical error correction code scheme (using a Viterbi decoder, like in this article), then things might be a bit easier. Maybe instead of 5 very stable qubits, you could have 20 sort-of-stable qubits, where you expect that half of them will be lost to noise. It would still be a net win.
Re:This could be huge (Score:4, Funny)
A big part of the problem with building quantum computers right now is keeping the qubits stable. The real world is constantly trying to "observe" (or interfere with) the qubits. When that happens, your quantum states break down and you lose your computation. This is a bit reason why we've only been able to build small (5-qubit) machines: it's very hard to keep things isolated and stable.
[Emphasis added]
I think the qubits' behavior is very suspicious. Surely if the qubits have nothing to hide, they shouldn't have any problems!
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Stop looking at me!
Also, there's nothing under this huge tarp. Nope. Nothing at all...
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Ah, you mean how engineers steal physicists' research papers and make money off of their ideas? Then yes literally, engineers are indeed "behind" physicists, screwing them over.
I hope you don't really believe that.
For starters, the myth that mathematicians have ideas, which physicists steal, which engineers steal, is bogus. There's feedback in all directions. Since the way in which ideas percolate from math through physics into engineering is often talked about, I'll only talk about the reverse process. Thermodynamics, arguably the most fundamental of physical theories, was developed in the study of how to engineer better steam engines. Calculus was invented in the study of mec
Get the full Ph.D. thesis here: (Score:5, Informative)
TFA is a bit short on details, as expected for a general-audience press release. In particular, they throw the word "Viterbi" out there without ever explaining what the heck it means; probably an artifact of USC containing the *Viterbi* School of Engineering. The juicy technical bits can be found in his thesis here:
Title: Quantum Coding with Entanglement ... and for a basic overview of the underlying concepts, of course the Wikipedia page on the Viterbi algorithm [wikipedia.org] is helpful.
Authors: Mark M. Wilde
Thesis PDF [arxiv.org]
Screw Bob and Alice (Score:1)
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It's in the cake-box along with the cat. As soon as we know the state of the cat, we'll know the state of the cake.
Frank (Score:1)
Frank Shoemaker would call this noise.
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Is that you, employee #[1A]FC?
Obvious? (Score:1)
Is it just me, or is the basic idea really rather obvious? (At least for someone with a basic understanding of both quantum computing and coding theory)
That is, it's fairly obvious you can use convolutional codes with qubits, and if you did you could use the viterbi algorithm to decode it without destroying/measuring the original qubits.
With that said, reliable communication of qubits may be particularly important for scale in quantum computing -- we can build a large quantum computer out of a network of sm
Violation of speed of light "speed limit" (Score:2)
Say you have a pair of entangled atoms, photons, whatever - and you move one of them across the universe (assuming you could keep the entangled state) and you flip the bit on the one back home. According to what I understand about entanglement, the particle on the opposite side of the universe immediately flips as well. Doesn't this violate the basic rule that the speed of light is the speed limit for the universe?
Als
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