Slashdot Mirror
The Viterbi Algorithm and Quantum Communications
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.'"
So . . . when is ANYTHING Alice says not garbled?
-----
Spoken like a true married man.
Beer is proof that God loves us and wants us to be happy.
I wish Alice and Bob would just go ahead and do it already. Everybody knows they have the hots for one another.
Who the ---- is Alice?
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.
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
> 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?
And for those of you wondering...
Markov was Chekov's evil twin on Star Trek.
Intron: the portion of DNA which expresses nothing useful.
Just one nit to pick.
Generally, we are talking about hidden markov models. linky
So you're suggesting Bob and Alice get entangled? That's spooky... too bad we wouldn't be able to watch.
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.
crucial, because opening it destroys it; and if it is garbled, he has nothing.'"
In other words, Bob doesn't have a date with Alice. He is not smiling anymore.
Say you had.... a buttload of code
And the imagination of slashdotters keeps on bewildering me! I salute you sir!
You are of course, correct.
But.... that's the only nit? I shall declare this a win then. :)
Thanks
Again, the engineers are behind the physicists.
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 is helpful.
Authors: Mark M. Wilde
Thesis PDF
a buttload of code... why would I want a context free grammar for the goatse guy? I'm statistically likely to be disgusted.
Uh, thanks. I'm still wondering what use this has.
Faster! Faster! Faster would be better!
Good article about Viterbi himself is here: http://www.wirelessweek.com/article.aspx?id=160380
I just wanna know when I can have my cake and eat it too.
If you quote this signature there'll be 72 copies of Windows ME waiting for you in Heaven.
How much is a buttload as expressed in Metric Fucktons? I only deal in Metric.
0xB315AA8D852DCD3F3DCA578FD2E0BF88
Frank Shoemaker would call this noise.
Wouldn't the communication already be compressed, thereby removing any detectable redundancy/structure?
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 at the Old Country Buffet, so be prepared to adjust accordingly.
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 small ones if we can reliably communicate qubits between them.
Ok, I've never understood this. I'm sure someone smart out there has the answer.
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?
Also, you need not move the entangled whatever across the universe; even if you moved it five feet away and it "instantly" flipped, this would still violate the laws of physics.
I'm sure I'm missing something here - what is it?
If you can read this... 01110101 01110010 00100000 01100001 00100000 01100111 01100101 01100101 01101011