KentuckyFC writes "One of the cornerstones of modern physics is Claude Shannon's theory of communication, which he published in 1948. If you've ever made a phone call, watched TV, or used a computer, you've got Shannon to thank for describing how information can be moved from one place in the universe to another using an idea called the channel capacity. But nobody has been able to develop a quantum version of this theory. So physicists have no idea how much quantum information can be sent from one point to another. Now two American physicists have made an important breakthrough by proving that two quantum channels with zero capacity can carry information when used together. That's interesting because it indicates that physicists may have been barking up the wrong tree with this problem: it implies that the quantum capacity of a channel does not uniquely specify its ability for transmitting quantum information (abstract). And that could be the idea that breaks the logjam in this area."
by Anonymous Coward
on Tuesday August 05 2008, @09:46PM (#24491043)
Now two American physicists have made an important breakthrough by proving that two quantum channels with zero capacity can carry information when used together.
So who wants to join my class-action lawsuit against math teachers?
Clearly the channels had SOME capacity for information transfer.
There are plenty of reasons why people don't understand quantum mechanics. Most people just don't care.
But I can list plenty of better reasons, for example, Calbi-Yau space. If you imagine the rubber-sheet model of the universe that everyone has seen in physics, replace it with this instead. Its pretty accurate as far as the math goes, and is a spin-off of QM. And then there are all of the various thought experiments, like Schrödinger'
The real question in my mind is whether this allows for FTL communication, or whether nature conspires against that once again?
I believe it's Bell's inequality that prevents information from traveling faster than light. But each of these channels does NOT transmit information, if the paper is to be believed.
So, does that mean they could somehow be used with entangled photons or whatever to transmit information faster than light?
At the end of my Physics degree, I had the option of continuing in Physics academia, or going into the world of work.
I'm sad to say that the main reason I wanted to leave Physics, despite somehow managing to retain a small fragment of my initial enthusiasm for the subject, was looking round at the professional physicists who took my course, and realising I really didn't want to spend the rest of my productive life surrounded by these people.
I'm not sure how useful this is. The summaries seem to say that if you take two or more channels that have a signal to noise ratio of zero, there's some potential for binding them into a useful channel, but there's no indication of what kind of recovery rate there can be gained from this. Is this just error-correction applied to an extreme?
You can extract immense amounts of information
from the combination of Fox News (channel 0 with no signal) and the White House Press Secretary (channel 1 with no signal).
Anything in common is a lie, and that is useful information.
Not a S/N ratio of zero, their definition of channel capacity is only very tenuously connected to Shannon's channel capacity really. Quantum channels already have 0 capacity at non zero fidelity (the quantum equivalent to S/N). The 0 capacity channel from this paper aren't 0 capacity because of their fidelity though, the channels are 0 capacity for different reasons.
So it's not really directly applicable, "just" interesting math.
The recent Amateur radio mode called WSPR [princeton.edu] ('whisper') can work with a signal around 27 dB below the noise (SNR of -27dB). This site [wsprnet.org] records contacts between hams worldwide in real time. Most activity is on 30m.
by Anonymous Coward
on Tuesday August 05 2008, @10:58PM (#24491699)
Most submissions to ArXiv do get submitted to peer-reviewed journals; this one claims to have been submitted in June (although they don't specify where). It's an opportunity for researchers to share their work without the delay of waiting for publication. Usually, papers there do get revised after going through the referee process.
We also get news from blogs, apple fan sites, and wikileaks. Non of those is peer reviewed either. The point is that it's not that people should take articles sourcing ArXiv with a grain of salt; it's that they should take everything with a grain of salt.
"Just saying, it needs to be taken with a grain of salt."
This is SLASHDOT. Everything here should be salted, marinated in salt water, then baked in an encrustation of rock salt for 8 hours before consumption.
Harry "Hello Jim Im ringing you back regarding the message you left on my voice mail."
Jim "What message ? I hevent left one yet"
Harry "Aw crap I did it again, I will never get my head around our new quantum telephone system"
Interesting, but the paper seems to have a nasty habit of simply redefining what "capacity" means in a quantum context, to basically, "Well, if we have two interacting channels, one changes the other to have non-zero capacity." And if I interpret it that way, it simply rewords the problem to be different from the original interpretation. Also, there's a significant amount (even for an arxiv paper) of speculation present (which is interesting!). From the paper: Nonetheless, each channel has the potential to \activate" the other, effectively cancel- ing the other's reason for having no capacity. We know of no analog of this effect in the classical theory. Per- haps each channel transfers some different, but comple- mentary kind of quantum information. If so, can these kinds of information be quantfied in an operationally meaningful way? Are there other pairs of zero-capacity channels displaying this effect? Are there triples? Does the private capacity also display superactivation? What new insights does this yield for computing the quantum capacity in general?
One "classical" analogy is that of orthogonally-crossed polarizers, which, upon insertion of another polarizer with principle axis somewhere between that of the originals, will allow light to shine through where none was before.
I think that Khashishi has got the essence of the 0+0>0 thing here. I haven't completely penetrated the noise in the Smith/Yard ArXiv article yet, but I'd bet my money that it boils down to this:
Take two channels in each of which all bits are completely random, and independent of the information that you wish to send. Let each bit of your information determine the correllation or anticorrellation of corresponding bits in the two channels, by introducing a quantum constraint between them before their actual random values are determined. Then, as in Khashishi's description, the xor of the two random channels is the message.
The only difference I detect in Smith/Yard vs. Khashishi is that they use quantum trickery to make the whole thing look symmetric. Neither of the random channels predates the other. Each one, evaluated singly, appears to be completely independent of the encoded message. In Khashishi's description, the time sequence in the construction of the two random sequences makes one of them seem a priori random, and the other to be a one-time pad encoding of the message, while in the Smith/Yard article you can't tell which is which.
It seems more like a meretricious way of telling a causal story about a well-known phenomenon than something truly "essentially quantum."
In Khashishi's description, the time sequence in the construction of the two random sequences makes one of them seem a priori random, and the other to be a one-time pad encoding of the message, while in the Smith/Yard article you can't tell which is which.
One-time pad ciphertext does appear to be random. Shannon proved that it has perfect secrecy.
<quote> One-time pad ciphertext does appear to be random. Shannon proved that it has perfect secrecy.
</quote>
Right. But Smith/Yard make a stronger claim than randomness. They claim that the content of each channel does not depend on the message at all. Once the one-time pad is determined, the encoded message is determined completely by the plaintext. By encoding the plaintext into a quantum entanglement prior to the creation of either random channel, they are able to tell a story in which each c
Channel theory link broken (Score:5, Insightful)
Actual link: http://cm.bell-labs.com/cm/ms/what/shannonday/paper.html [bell-labs.com]
Re:Channel theory link broken (Score:5, Funny)
You fools! You've gone and changed the article by clicking the link.
Parent
Re:Channel theory link broken (Score:5, Funny)
Parent
Re:Channel theory link broken (Score:5, Funny)
Links in Slashdot are simultaneously dead and alive! Clicking on them decides which ;)
Parent
Re: (Score:3, Funny)
Re: (Score:3, Funny)
Just don't take your cat to any Eastern bloc countries. In Soviet Russia, TFA slashdots YOU!
So 0+0=1! (Score:5, Funny)
Now two American physicists have made an important breakthrough by proving that two quantum channels with zero capacity can carry information when used together.
So who wants to join my class-action lawsuit against math teachers?
Re:So 0+0=1! (Score:5, Funny)
I do!
That makes three of us!
Parent
Re:So 0+0=1! (Score:4, Interesting)
Parent
Re: (Score:3, Informative)
1=0+0!
There, fixed that for you.
quantum mechanics (Score:5, Interesting)
Feynman once said that nobody understands quantum mechanics, and this is why.
Re: (Score:3, Interesting)
Clearly the channels had SOME capacity for information transfer.
There are plenty of reasons why people don't understand quantum mechanics. Most people just don't care.
But I can list plenty of better reasons, for example, Calbi-Yau space. If you imagine the rubber-sheet model of the universe that everyone has seen in physics, replace it with this instead. Its pretty accurate as far as the math goes, and is a spin-off of QM. And then there are all of the various thought experiments, like Schrödinger'
Re:quantum mechanics (Score:5, Funny)
Parent
FTL communications? (Score:3, Interesting)
The real question in my mind is whether this allows for FTL communication, or whether nature conspires against that once again?
I believe it's Bell's inequality that prevents information from traveling faster than light. But each of these channels does NOT transmit information, if the paper is to be believed.
So, does that mean they could somehow be used with entangled photons or whatever to transmit information faster than light?
Re:quantum mechanics (Score:5, Informative)
Conversely if two physicists walk into a bar, how many patrons have lives?
Answer: The same number as there were before they entered.
In my experience physicists are generally rather cool, worldly people who have well developed personal lives.
Parent
Re:quantum mechanics (Score:5, Funny)
PHYSICIST!
you outed yourself!
Parent
Re:quantum mechanics (Score:5, Insightful)
Parent
Re: (Score:3, Funny)
Yeah, I mean look at that bitchin' goatee Freeman is sportin'!
Re: (Score:3, Funny)
Let's not forget the crowbar.
Encryption is anti-american (Score:5, Funny)
When you use quantum encryption, the theorists win !
Simplified Quantum Physics (Score:2, Insightful)
Try not to look directly at it...
Two channels with zero capacity can carry info (Score:5, Funny)
It was called ISDN.
Re: (Score:3, Insightful)
For a second... (Score:2, Funny)
Re: (Score:3, Funny)
Two Channels with Zero Capacity? (Score:5, Funny)
I c u d h l w t q a t m r p o r p y
h h t o n s i e g e t d a
t o l e p i h u n u c y t g a h .
RS
Re:Two Channels with Zero Capacity? (Score:5, Funny)
I demand you take that back. My grandmother was a saint!
Parent
Re: (Score:3, Interesting)
Zero plus Zero equals One for large values of Zero (Score:5, Interesting)
I'm not sure how useful this is. The summaries seem to say that if you take two or more channels that have a signal to noise ratio of zero, there's some potential for binding them into a useful channel, but there's no indication of what kind of recovery rate there can be gained from this. Is this just error-correction applied to an extreme?
Re:Zero plus Zero equals One for large values of Z (Score:5, Funny)
You can extract immense amounts of information from the combination of Fox News (channel 0 with no signal) and the White House Press Secretary (channel 1 with no signal).
Anything in common is a lie, and that is useful information.
Parent
Re:Zero plus Zero equals One for large values of Z (Score:4, Informative)
Not a S/N ratio of zero, their definition of channel capacity is only very tenuously connected to Shannon's channel capacity really. Quantum channels already have 0 capacity at non zero fidelity (the quantum equivalent to S/N). The 0 capacity channel from this paper aren't 0 capacity because of their fidelity though, the channels are 0 capacity for different reasons.
So it's not really directly applicable, "just" interesting math.
Parent
Re: (Score:3, Interesting)
Non-peer reviewed (Score:5, Interesting)
Am I the only one who's worried that we keep getting 'news' from papers published on ArXiv, which is not a peer-reviewed source?
Just saying, it needs to be taken with a grain of salt.
Re:Non-peer reviewed (Score:5, Informative)
Parent
Re:Non-peer reviewed (Score:5, Insightful)
Parent
Re: (Score:3, Funny)
"Just saying, it needs to be taken with a grain of salt."
This is SLASHDOT. Everything here should be salted, marinated in salt water, then baked in an encrustation of rock salt for 8 hours before consumption.
Do NOT look at this message!!! (Score:5, Funny)
Hmm... (Score:3, Funny)
This is new? (Score:5, Funny)
Quantum Telepnone Calls (Score:5, Funny)
Re: (Score:3, Funny)
Original article here: (Score:3, Interesting)
http://arxiv.org/PS_cache/arxiv/pdf/0807/0807.4935v1.pdf [arxiv.org]
Interesting, but the paper seems to have a nasty habit of simply redefining what "capacity" means in a quantum context, to basically, "Well, if we have two interacting channels, one changes the other to have non-zero capacity." And if I interpret it that way, it simply rewords the problem to be different from the original interpretation. Also, there's a significant amount (even for an arxiv paper) of speculation present (which is interesting!). From the paper: Nonetheless, each channel has
the potential to \activate" the other, effectively cancel-
ing the other's reason for having no capacity. We know
of no analog of this effect in the classical theory. Per-
haps each channel transfers some different, but comple-
mentary kind of quantum information. If so, can these
kinds of information be quantfied in an operationally
meaningful way? Are there other pairs of zero-capacity
channels displaying this effect? Are there triples? Does
the private capacity also display superactivation? What
new insights does this yield for computing the quantum
capacity in general?
One "classical" analogy is that of orthogonally-crossed polarizers, which, upon insertion of another polarizer with principle axis somewhere between that of the originals, will allow light to shine through where none was before.
Re:similarly, in computer science, (Score:5, Funny)
Does the data really have to be copyrighted for that to work?
Parent
I think you've got it (Score:5, Interesting)
Take two channels in each of which all bits are completely random, and independent of the information that you wish to send. Let each bit of your information determine the correllation or anticorrellation of corresponding bits in the two channels, by introducing a quantum constraint between them before their actual random values are determined. Then, as in Khashishi's description, the xor of the two random channels is the message.
The only difference I detect in Smith/Yard vs. Khashishi is that they use quantum trickery to make the whole thing look symmetric. Neither of the random channels predates the other. Each one, evaluated singly, appears to be completely independent of the encoded message. In Khashishi's description, the time sequence in the construction of the two random sequences makes one of them seem a priori random, and the other to be a one-time pad encoding of the message, while in the Smith/Yard article you can't tell which is which.
It seems more like a meretricious way of telling a causal story about a well-known phenomenon than something truly "essentially quantum."
Parent
Re: (Score:3, Informative)
In Khashishi's description, the time sequence in the construction of the two random sequences makes one of them seem a priori random, and the other to be a one-time pad encoding of the message, while in the Smith/Yard article you can't tell which is which.
One-time pad ciphertext does appear to be random. Shannon proved that it has perfect secrecy.
Re: (Score:3, Interesting)
One-time pad ciphertext does appear to be random. Shannon proved that it has perfect secrecy.
</quote>
Right. But Smith/Yard make a stronger claim than randomness. They claim that the content of each channel does not depend on the message at all. Once the one-time pad is determined, the encoded message is determined completely by the plaintext. By encoding the plaintext into a quantum entanglement prior to the creation of either random channel, they are able to tell a story in which each c
Re:I think you've got it (Score:4, Funny)
Like putting too much air in a balloon! :-D
Parent
Re: (Score:3, Funny)
> We'll have human sacrifice, dogs and cats living together... mass hysteria!
you mean like Los Angeles ?
Re:similarly, in computer science, (Score:5, Funny)
...and if I combine your post with a random pad of 1s and 0s, will I get something that has anything to do with TFA?
Parent
Re: (Score:3, Funny)
Meaning two blondes make a brunette?
Only if they are of different gender, and with 25% [wikipedia.org] chance :-)