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Single Photons Bounced Off Orbiting Satellite
KentuckyFC writes "If we're ever going to benefit from the perfect security of quantum communication, we're going to need ways of transmitting entangled photons around the globe and certainly further than the current record of 144km through the atmosphere. Anton Zeilinger at the University of Vienna and colleagues have taken an important step towards this by bouncing individual photons off the Ajisai geodetic satellite (essentially a space-based disco ball) which is orbiting at 1400km. The group says the experiment is an important proof of principle for satellite-based quantum communications."
Not to mention photons are like words: you shouldn't use those you don't understand. Is it a wave or is it matter? Huh, Mr. Smarty Pants? Oh, what's that you say? A boson followed by a long explanation, how utterly predictable! Ha, you would say that. No. I want answers and I wanted them back when the church would persecute you for publishing them!
We need something smaller. Go back to the lab, anything larger than a Planck Length is unacceptable. And only 1400km? So help me god, if you can't express the distance it travels in double up arrow notation or tetration, I don't want to hear about it. Come on people, this is real science, not some religious mumbo jumbo (6,000 years? Is that the absolute limit of your imagination!?)
My work here is dung.
There's no place like localhost
This is just an elaborate game of pong, isn't it...
I record my sleeptalking
My work here is dung.
From my understanding it does serve a practical purpose in that intercepting the message changes it. Thus while you can't stop people from tapping into your message, you do have instant feedback about when that happens.
I am Slashdot. Are you Slashdot as well?
Supposed security improvements? This is the only truly secure method of communicating without a key exchange. This is the only thing we can fall back on after factoring is made "easy" by quantum computers. Maybe it's breakable in some future world, but for now it's our backstop for RSA. Have you ever imagined the implications of this world without public key encryption?
Ah, from some angles, this experiment proves the opposite. You need the photons to be "entangled". That means effectively in their own little world, not intereacting with the universe in any way. Shooting them up through 10^38 atoms of the atmosphere and bouncing them off a satellite is the exact opposite of entanglement.
Why so cynical, Viol8? This sort of research will often net us other technologies that can be used in all facets of our lives. I would agree that nothing is unbreakable. I would think that another quantum computer would eventually break some quantum encrypted packets.
Bearded Dragon
Call me Old School, but when I was a kid, we had this thing called Heisenberg Uncertainty. Obviously, with the advent of Dark Matter, Quantum Entanglement and a Beowulf Cluster of XBox 360's, we don't need to worry about that.
Humor your old man... tell me how we got around that?
Scientists later found that the photon had been Photoshopped.
It must have been something you assimilated. . . .
Real security improvements. There is no proof that there is not a trivial way to factorise multiples of large prime numbers, which is the basis of most current encryption standards. There are alternatives, but again there is no proof that these cannot be cracked quickly.
;-)
Even though it is unlikely that someone will have a mathematical breakthrough that would allow your PDA to break 2kb keys, we know that a lot (maybe all) of these algorithms could be cracked with a quantum computer. It is possible that the US NSA already has such a computer, maybe together with Russia, China and Bill Gates
Quantum encryption is proven to be uncrackable without showing that someone is listening. With a preamble of two-way communications you can have a connection that is proven to be absolutely secure, and no breakthrough in mathematics or technology will break it.
If the photon has to get from point A to point B, then what is the advantage to quantum communications? Is it because the photon can be sent _before_ the data, which will then be sent by entanglement? Can someone explain it so my dumb mechanical engineering ass will understand it? I'm sure I'm not the only one who'd love to hear it. Thanks.
It is dangerous to be right when the government is wrong.
People are still puzzling over how the world's largest rave got started. It seems that once a light show started from what appeared to be a giant disco ball in space people everywhere got out their glow sticks, drugs and pacifiers and started dancing.
You are using English. Please learn the difference between loose and lose; they're, there, and their; your and you're.
Breaking quantum cryptography is not hard, it is impossible. The security is guaranteed by the laws of physics. Unless quantum mechanics is flat out wrong, it can never be broken, period. And saying quantum mechanics could be wrong is like saying gravity could be wrong.
About quantum computing, it's actually closer to providing new computational powers than you might think. In terms of a powerful, programmable computer that can factor large numbers, we are a long way off. But in terms of being able to simulate certain quantum systems that current supercomputers cannot, we are fairly close.
We got a decent firing photon cannon.
Absolute power corrupts absolutely. indymedia
A huge advantage of quantum communication is that if someone DOES read the transmission somewhere in between (a middle-man attack) then this is detectable, as it alters the transmission in the process of reading it. Digital transmissions do not have this property. So even if you send data in the clear (stupidly), you'd know if someone else read your data before it got to you.
All theoretically of course.
How can they possibly align the mirror so that a single photon bounces back to the detector? Surely a single-atom imperfection would be enough to deflect it across the room, and a few atoms would deflect it to the next country
I am expecting some quantum genius to tell me that it doesn't matter if it misses the detector because one from a parallel universe will hit it anyway!
Existing cryptography is based on difficult mathematics. RSA, for example, is equivalent to finding a prime factorization of a very large number. By "equivalent" I mean that factoring the number is sufficient to break the encryption, and breaking the encryption (even if you managed to do it without actually attempting to factor the number) tells you the prime factors, so you can't do one without also doing the other. If you developed an incredibly fast, novel way of breaking RSA, you would also have developed an incredibly fast, novel way of factoring large numbers, and vice versa.
So RSA is directly tied to the difficulty of factoring large numbers. As long as that remains difficult, RSA remains difficult. The second someone comes up with a fast way to factor large numbers, RSA is shattered. It's similar with other encryption algorithms -- they all fundamentally rely on certain mathematical operations being "hard". Since we generally can't prove there's no more efficient way to solve these mathematical problems, and our rapidly increasing computing power continues to make "hard" a highly relative term, it's impossible to be completely confident in any of these algorithms.
Quantum communication is different. Rather than relying on hard mathematical problems, it relies on the laws of physics. You can't intercept quantum communications without changing the signal in an obvious and measurable way which would instantly alert the communicating parties. There's no algorithm to crack, no mathematical puzzle to solve. It's just the basic properties of light that make it impossible to intercept the photons without being noticed.
Of course it's still possible that quantum communication could be "cracked" -- but the only way that would be possible is if our understanding of the laws of physics is incorrect. "Cracking" quantum communication would be basically the same as building a successful perpetual motion machine (and thereby "cracking" the laws of thermodynamics) -- yes, it's theoretically possible that our understanding of physics is flawed and therefore our trusted "laws" aren't actually true, but... well, how long has it been since any of the basic known laws of physics have been shown to be completely incorrect? I mean, even Newton's 300-year-old laws aren't really wrong -- they're extremely good approximations that work essentially perfectly for all but very high energy situations. My money's on the physicists with this one.
ZFS: because love is never having to say fsck
With quantum computer I'd assume would come quantum cracking. This is the whole seemingly apparent dualistic nature of this universe in that either one side or the other will be ahead (encryption vs crackers, good vs bad, etc), and that will not last forever. Very wavelike all things can be when you see the binary facts to be merely the expression of the relative positions of two observed events. The crest and trough of waves are two of the three distinct points in waves that can be observed, the third being 'neither'...
I would gather that this is another medium of long-distance communication that uses less energy than current ones do. You do know how saturated the spectrum of communication is, so why nay-say a possibly useful advancement that is in testing and research stages. Innovation is always welcome as long as it serves some sort of purpose, but your skepticism is most likely warranted.
Although is it particle communication or wave communication? If it were a wave then it would just be another wavelength of radiation to shoot into space. And I'm not even sure if particle communication is a real term, but a quick google proves me wrong (or right).
Absolute power corrupts absolutely. indymedia
i'm not sure it would use less energy, i think it would actually use more, because quantum communication can only work together with a classical communication channel.
you cant actually send information using the quantum channel, because you cant control it. you can only compare it to the classical channel. the quantum channel gives you random bits, and the classical channel tells you whether each bit is correct or the opposite of what it should be.
Intercepting (and breaking) quantum crypto is very much so possible. If Charlie intercepts Bob's fotons on their way to Alice, and Charlie can transmit the very same fotons he just recieved, he can intercept the message succesfully without Alice or Bob ever noticing (perhaps a lag because Charlie has to do some work before he transmits). What Charlie cannot do is old style wiretapping: every foton is a carier of one bit and reading it causes the bit to flip and thus Alice knowing the line is tapped. Reading the foton, throwing that foton away and sending another foton with precisely the same orientation/spin as the foton he recieved to Alice will be undetectably. Never mind that in practice not now and probably not you can have 1 foton = 1 bit, but you'll need a group of fotons = 1 bit. And when there's a group, there's room to play for a wiretapper.
Now you can be POSITIVE that it is your own backscatter! Go on, DoD, start DROOLING!
And yet again the moderators on here prove that anyone who dares to question the prevailing "wisdom" on /. gets marked as a troll.
The Heisenberg Uncertainty Principle is not a physical "law" rather it is a summation of other observations and it has been "short-cutted"
Imagine, you May have a quantum entangled pair in a box. How do you know if the box is full? If you shine anything in you will disturb the pair. So you send a single photon through a beam spliter. One path is clear the other goes through the box. The beams then recombine to create an interference pattern. Since you slit the single photon, it has a 50/50 shot of sending the photon through the box.
Now, if the box and it is empty then the beam(s) will create an interference pattern regardless of the path. If the box is full and the photon goes through the box then no light will be detected (and the entagled pair ruined). BUT if it goes down the open path and there is something in the box then there will be no interference pattern.
You have just shown that position of an object in the box without effecting it. You have just violated the HUP.
Now in the above design you have a 50/50 shot of sending the photon through the box. But as it turns out, so long as there is a "chance" that it COULD go through the box, the experiemnt still works. Therefore you can add additional beam splitters between the box and the 1st splitter, directing one side into the open path, increaing the success rate to and arbitrarily high level.
I refer you to the no cloning theorem. And you are correct, that in practice there is a probability that there can be more than one photon per bit sent. However, there are ways of correcting for this such as privacy amplification. The guys who are doing this stuff are smart. They know what they're doing. Physicists don't throw around terms like "provably secure" lightly.
The German Enigma machine from WWII was fairly uncrackable, even for the decoders at Betchley Park, but the German operators got lazy, and weren't following proper procedures, which allowed Turning et. al. to get a toehold into the crack.
The One Time Pad is provably unbreakable, but the British were able to decypher Soviet OTPs, because they had reused the pads after a year, thinking no-one would go back that far. One of our Admirals did the same thing, but there's no evidence he got caught.
The obvious back door to a quantum crypto machine would be the operator, or some part of the process before the plaintext is encrypted. Just because physics says that the process is unbreakable, doesn't mean the machine can't malfunction, and the malfunction may not be detectable by the operator. i.e. perhaps the machine can detect any malfunction, but the indicator light that tells the operator is broken.
Even though OTP is provably secure, the military proceeds and ends each message with gibberish, to throw off attempts at decoding.
All ideas^H^H^H^H^Hprocesses in this post are Patent Pending. (as well as the process of patenting all postings)
I am not a particle physicist, nor do I possess anything other than an ameteur's grasp of how this stuff works.
One potential use for quantum entanglement is to use a whole slew of entangled photons that can be used to transmit binary information at an arbitrary bit-width. While transmitting via the quantum channel, you also transmit via a classical channel some minimal information to discern the clock and parity for decoding the quantum information at the other end.
The reciever continually records the information streaming out of the quantum entangled photons, and then buffers it for later, at such a time it can be decoded after the classical component has been recieved.
The result is practically interference free, EM bandwidth friendly (your classical channel is likely optical or radio), and reasonably secure thanks to the actual data moving via a quantum channel. This also plays well with the lightspeed barrier, relativity and the quantum nature of the medium in general.
For example, take a satellite taking *very* high resolution images of Mars while in Martian orbit. It would send these gigabyte-sized raw images via the quantum channel and transmit the parity/decode/clock info via radio. Back on earth, the quantum bit-buffer is just happily logging 1's and 0's round the clock, blithely unaware that it now has real data. Some time later, Mission Control finally "catches" the complete radio transmission, deduces when it was sent, and decodes portion of the quantum buffer for that timeframe. Presto. Seriously high-bandwith, high-latency, inter-planetary data transmission.
Oh great...
I can't wait until someone at the RIAA figures out how to protect music with quantum DRM. You get to listen to a song ONCE, then it doesn't exist anymore.
They will charge PER listening.
- For the complete works of Shakespeare: cat
Because
/you/ havn't a clue but cant stand someone else did or tried to.
A) I'm Dutch so I wrote foton, not really thinking about it. I'm sorry that's wrong, but please... that's under no condition a reason to question someones intellect.
B) having actually done an experiment together with my prof on the subject (I was a first year physicsstudent back then).
C) The no cloning theorem: when we measure a photon (see what I did there?) its state known and its state can be changed. It doesn't matter what its state is going to be, because we discard it, as long as we give the new photon the correct properties.
D) Physisists can be extremely enthousisatic too and don't check for loopholes (wiretapping is still impossible, just sitting in between (which most of the time is impracticle but very much possible isn't). Above all they sometimes forget about the practicle problems of engineering such a device.
E) My prof confirmed my suspicions on the subject.
So, if I'm wrong, please correct me, but spare me the "these are physisists and you havnt even read the wiki"-talk. That just makes me feel
If you create an acct, (as I have) you can set it to the old version in your prefs. I hate the new layout as well.
My Babylon
People have been bouncing single photon's off of the Moon for almost 40 years, using Lunar Laser Ranging, or LLR.
Typically, with LLR a dense "pancake" of photons (maybe 1 meter across and a few mm deep) is shot at the LLR site on the Moon, and one photon returns per shot.
Ajisai is a relatively large Japanese satellite intended for Satellite Laser Ranging (SLR). Even though the SLR return is typically many photons, not just one, the ratio of (photons received back / photons sent) is still extremely tiny, and I rather doubt that they are sending one photon up to get one back.
So, this sounds more like a press release than an actual advance.
Most Expensive Disco Ball...Ever!
Hi,
I am a theoretical particle physicist, and I understand what you are trying to say, and I understand what the replies are saying as well.
You are correct that the 'basic' quantum cryptography that is taught can be hacked. This is just because a simplified version is used in books, because it's confusing enough.
Others who point out the no cloning principle are exactly right. You cannot read and then reemit a photon with the same polarization (for example). Basically the way it work is like this:
Alice picks one of four polarizations at random, out of vertically polarised (0 degrees, say), horizontally polarised 90 degrees), or polarised at 45 degrees, or at -45 degrees.
Bob then picks, at random, whether to measure the polarization horizontally/vertically or to rotate his polariser 45 degrees and measure at 45 degrees or at -45 degrees.
If Bob chooses the 'wrong' direction, he'll get a random result. If he chooses the 'right' direction, then he'll get the correct result. After this is done, Alice tells Bob how she sent it, and Bob can discard all the measurements in which he chose the wrong direction to measure in. If Bob tells Alice the same results that Alice sent, then they know there was no interference.
There is no way to measure the 'true' polarization of the light that Alice sent, because you have to have your polariser either measuring horizontal/vertical, or measuring at 45/-45. You can't have it do both. So noone can monitor and then reemit a photon with the same polarization.
Would make for an interesting game of pong!
I misread both the title and the summary. I got:
....
Simpletons bounced off orbiting satellite.
at the University of Vienna and colleagues have taken an important step fowards by bouncing this individual Anton Zeilinger off the Ajisai geodetic satellite
...
It's been a long Monday.
GP meant quantum encryption is still vulnerable to man in the middle attacks.
http://en.wikipedia.org/wiki/Quantum_encryption#Man_in_the_middle_attack
Ok, I can buy this.
I think we are talking about two different parts of the HUP. While you did a fine job describing the "state" of the photon, I guess I was referring to specifying the "position" of the photon. If specified tight enough to hit the mirror, the HUP effect on momentum was enough to make the error cone bigger than the mirror.
But I was also taught that the Universe was going to re-collapse and that moon craters were volcanos.
Now, either get off my lawn or help me with this Beowulf Cluster of XBox 360s!
Quantum cryptography isn't actually cryptography. It's a tamper-resistant method of transmission. In other words, it will tell you when someone is reading your message enroute. It does not encrypt the message. You do that with the same old cryptography routines, quite likely prime number based. As you pointed out, these are quite crackable. The difference is, you KNOW when someone read your message.
Nobody has yet proven that you can do non-trivial things with quantum computing that you can't do with normal computing, or even that you can do the same old stuff faster. There's considerable well founded doubt that its even theoretically possible, never mind practical. Simulating quantum systems with quantum systems, while useful, is not a non-trivial computation task. That's like me saying that I can achieve nearly instantaneous raytracing performance by taking photographs of a scene.
Others have created quantum crypto systems that take the possibility of cloning into account, http://w3.antd.nist.gov/pubs/Mink-SPIE-One-Time-Pad-6244_22.pdf
'basic' quantum cryptography that is taught can be hacked This is true but I think not for the reasons you believe. Basic quantum crypto provides confidentiality only. To keep from being hacked, you must provide authentication as well (Alice must be able to prove she is communicating with Bob and not Eve). I haven't heard of a way to do this without falling back onto more conventional cryptographic techniques such as RSA signatures - at least when doing quantum crypto over fiber. Maybe sending photons through the atmosphere means you can actually just see if somebody is acting as a man-in-the-middle.Hemisphere-wide disco dance party everybody!!!!
\o|>
I agree with the parent that QC certainly provides incentive for researchers to get that big fat check, but would like to mention the IMO the main benefit of QC is not security but speed. "Spooky action at a distance" is also instantaneous action at a distance. If we can get an entangled pair (or eventually an entangled set) of photons, electrons, or whatever particle to exist such that one exists at NASA HQ and one in the space station then the communication delay is effectively zero. NASA can pick up the phone, so to speak, and talk to astronauts in real time with zero delay as if they were standing in the same room. Also since the delay is zero the only bottleneck in the processing time to decode the state change to determine the next bit or qubit or whatever they decided to call it in quantum computers. In theory, this is also zero in a fully quantum computer, that is to say the change is 'noticed' by the receiving quantum computer instantly so the bottleneck becomes displaying this change for the user to see which is equivalent to the minimum of the bandwidth of the GPU and the refresh rate of the display. If these can ever be made into quantum electronics (which if the quantum computer ever exists, surely they can) then the only limitation is our eye (for a graphical display of the communication) which means we will perceive instant communication for any distance and further that a single entangled pair has effectively infinite bandwidth since data is computed/displayed as a quantum process which is so fast we as humans will never see any delay.
I quit smoking, thus I have no sig.
Except that practically, you can stop people from intercepting the communications, by the very aspect you point out.
While the connection is sending data merrily along its way, upon the first bit being intercepted, both ends know this, thus naturally should be programmed to stop communicating at that point.
Once communication is stopped, the interception of useful data has been prevented.
Granted, this is vulnerable to a pretty bad DoS attack, but that was never its goal to prevent, only to prevent interception.
you cant use (only) a quantum communication channel to communicate, because you cant control what values are sent. they're random. you have to use a classical communication channel together with it. the data sent through quantum entanglement is meaningless until you compare it to data sent via the classical channel.
so there is no speed increase. you cant communicate faster than the speed of light.
This is the impossible part. It can't be done. and Charlie can transmit the very same fotons he just recieved, Again, there is no physical way in quantum mechanics to do this, it is impossible. he can intercept the message succesfully without Alice or Bob ever noticing (perhaps a lag because Charlie has to do some work before he transmits). Yes, if he can do two things prevented by the laws of physics, then he can do a lot more than just intercept messages, he could travel millions of times faster than the speed of light too (since that is equally impossible) and go back in time and [insert favorite scifi plot here]
Saying that quantum crypto is unbreakable is a bit overstating the facts. The current suggestion is that quantum crypto should replace public key crypto for key exchanges. After the exchange, the data stream would likely just proceed with a typical AES (or whatever symmetric algorithm seems strong at the time) session.
Quantum crypto can be used for the entire session, but the overhead is enormous.
Also, keep in mind that quantum crypto does not prevent people from intercepting the messages, it just makes sure that when the messages are intercepted, it is detectable.
W3 h4v3 ur ph070n. F u 3v3r w4n7 70 s33 17 4g41n, u mus7 ...
Who would win this election: Andrew Weiner vs Andrew Weiner's weiner.
It isn't that quantum encryption is unbreakable, it's that a one-time random pad cipher is unbreakable, mathematically. Quantum encryption is a way to securely transmit a one time random pad, which is effectively 100% secure if implemented correctly. In the standard protocol, there is roughly a 1/2^n chance of an Eve guessing correctly how to intercept the message, and you can send lots of test bits to make sure that this essentially never happens). This also, as others mentioned, lets you see if anyone is listening, so long as you design a protocol that checks for this. Again, unless Eve makes n correct 50/50 guesses for arbitrary n. (The randomness comes from the quantum randomness that happens from when you project a pure basis polarization state onto another basis that is 45 degrees rotated from the first one. It's the most fundamentally random process known to philosophy.) Quantum encryption protocols will probably be broken when someone finds a flaw in a sloppy implementation, or in the random number generators generating the bits being sent or bases being chosen, or something of that nature. It's very unlikely the physics of the transmission will be exploited, as quantum mechanics and its children are probably the best-tested and most closely scrutinized scientific theories in human history.
Yes, I made that analogy intentionally. Newtonian gravity is, of course, slightly wrong, but it's good enough most of the time. Whatever correction to QM we may have in the future, I think it is unlikely it will alter it in such a way as to make quantum cryptography breakable.
> Hmm. I think you meant you cannot read and reemit with 100% fidelity. http://www.icfo.es/images/publications/J05-055.pdf
I did not know about this - very interesting.
> This is true but I think not for the reasons you believe. Basic quantum crypto provides confidentiality only. To keep from being hacked, you must provide authentication as well (Alice must be able to prove she is communicating with Bob and not Eve)
That is the reason that I was thinking of.
The funny thing is, quickly factoring large numbers becomes useless as soon as it is possible. The only use is in public key encryption, and if everyone stops using public key encryption, then that application of quantum computers dies.
All theoretically of course.
And only with a passive MITM attack. There's nothing to stop the man in the middle from having his own receiver and transmitter, and acting like A to B and B to A, sending photons of his own in reply to each (an active MITM attack); at least not unless the parties have exchanged a short password beforehand.
Nah, you'd use a symmetric block cipher. RSA was invented to solve the key distribution problem, but if you have a quantum crypto link to exchange key material, you don't have a key distribution problem.
Note to ACs: I usually delete AC replies without reading them. If you want to talk to me, log in.
Good point.
I wonder what the lost photon rate is. If the photons tend to get lost then you'll have to frequently send replacements. I suspect that would change your eavesdropping detection rate from 100% to something lower.
Dear theoretical particle physicist,
I've read many claims by physicists that these "quantum entangled" particles need not be transmitted at all, but that by simply changing a particle at one location the other half of the entangled pair instantly changes too; even if one particle is on earth and the other on Pluto. They use this to argument as a supposed proof that causal law does not work the way it has been traditionally understood.
Now I read that we must transmit the entangled particles (just as we do with the ordinary ones). And that such transmissions can be intercepted. What's next, will I be told that the quantum computer can't output answers before the question has been input?
In most quantum protocols a one-time-key is sent using quantum mechanics and not the actual message. After you know that no one has tapped into the transmission of the key, you can send the encrypted text using any classical means. So there is no worry that you have to stop transmitting quickly to keep them from getting the message.
So yes, the quantum aspect only tells you if someone has tapped in, but that is enough to allow us to send completely secure messages.
(That isn't quite true. Quantum protocols assume you have another communication channel that is able to pass around authenticated but not secret messages (authenticated = the message sent is the message received and is from who it says it is; not secret = others might have overheard it). However, authentication is in general a lot easier to arrange. Quantum cryptography is basically takes an insecure quantum channel and an authenticated classical channel and turns them into a guaranteed secrecy key-distribution channel that is subject to DoS attacks. From guaranteed secrecy you can build most other things that crypo people are interested in.)
It is proven (Bell's inequality) that either one of the following two statements is false:
1. Objects have a definite state
2. The effect of changing something can't travel faster than the speed of light.
Quantum entanglement does show that the particles communicate faster than the speed of light (and thus have no regard for causality). However the catch is that information can't travel faster than speed of light. Information meaning information that we, as big classical beings, have access to. We are prevented from accessing this quantum information. We can't communicate to someone else faster than the speed of light. So causality in the 'big' classical world is never broken.
No you haven't violated the HUP. Your experiment has something to do with observer effect but I have no clue what it is supposed to prove. However, you haven't measured the position and velocity of the particle, so you havn't violated uncertainty principle.
What if Tetris was invented by Nazis?
The observer effect is a direct result of the connection between position and velocity.
My design has determined the position of an object (within the box) without effecting the speed whatso ever since I haven't interacted with it.
Most people confuse the difficulty of measurement with the uncertainty principle. The difficulty of measurement has to do with the fact that you can't measure something without affecting it. The uncertainty principle is actually a direct consequence of the fundamental postulates of quantum mechanics. You cannot, even in principle, even as a thought experiment, construct a quantum mechanical state which violates the uncertainty principle (or any of the uncertainty principles). This is a mathematical certainty; it follows using pure logic from the postulates of quantum mechanics.
The difficulty of measurement is merely a mechanism by which the uncertainty principle is "enforced". If the postulates of quantum mechanics are correct (ie, if they are physical "law"), then the various uncertainty principles are correct (physical "law").
You might read the relevant wikipedia section for more clarification. Also, get yourself a copy of David J. Griffiths An Introduction to Quantum Mechanics, and be prepared to work through a decent bit of math. It will improve your understanding of quantum mechanics greatly.
SIGSEGV caught, terminating
wait... not that kind of sig.
The FCC is already making plans to auction off the entire spectrum of quantum communications for billions of dollars.
I will continue to follow this with interest.
LedgerSMB: Open source Accounting/ERP
Say you create a polarized single photon. Any measurement of that photon will destroy it, and no single measurement will allow you to fully characterize it's polarization state. This is the foundation of Quantum Key Distribution (QKD). If somebody were to try to eavesdrop, she would have to intercept single photons and measure them, thereby destroying them. She could send new photons to replace the ones she measured, but enough would differ from what was originally being sent that the people trying to create a secure key would know there was an eavesdropper.
The experiment in the linked article operates by sending pulses containing on the order of 10^16 photons, all in the same state. An eavesdropper could simply intercept some of those photons and pick up the key without anyone knowing. In order for this setup to work with QKD, they would have to *send* single photons from the very beginning.
They claim 4.6 clicks per second in this experiment. If they sent single photons, that would come out to around 4.6 * 10^-16 clicks per second. This would be nigh undetectable with the dark counts they have, but let's assume dark counts weren't an issue. Pulsing at 17KHz would mean they could get 7.82 * 10^-11 bits of key per second. That translates to around 500 000 years to exchange a 128-bit key. That's not very practical.
Now, I really don't mean to bash them. Just aligning a satellite and getting any results at all is impressive. While what they have is not practical for actual QKD, the seed of innovation is there. Exciting stuff!
Oh wait ...
Gentoo Linux - another day, another USE flag.
Does this particular box also contain a cat?
Finally a novel use of the word 'Ping' We pinged the moon. Of course a trace route is trival since its basically line of sight.
Of course Richard Feynman thought of light as nothing more than particles, that behaived as summations of particle paths called path integrals. Q.E.D. is based upon that.
Take out a CD. Look at the rainbow. Q.E.D. proved.
I knew Einstien personally...er.. Hans... his son.
...for some brief entanglement and possible spooky action. Strangeness and charm a definate plus. Let's take a spin and hit the disco ball together. Must accept me for who I am - interfering observers need not apply. Will give you my specifics when you give me yours.
[The scientists couldn't send paired photons; they're too intimately entangled.]
The Wolfpack Project: BitCoin + Crowdfunding = Political Accountability
Actually, if you review the uncertainty principle, you find that uncertainty includes more than just position and velocity but in the quantum world it also includes entanglement with the environment. Having entangled particles adds a great deal of uncertainty since you don't know what the other particel in the pair is experienceing.
This is actually Bohr's solution to one of Einstein's thought experiments, although phrased differently. (Read up on the light in the box)
Therefore, you are partially correct. I was clumbsy with my terminology. The HUP allows for an elimination of the observer effect. Therefore you can determine both the position AND velocity to an arbitraily high percision by increasingly entangling it with the universe.
In this way, my device COMPENSATES for the HEISENBERG uncertainty principle. It is a Heisenberg Compensator.
What does this mean? Honestly I don't know. I first ran across this experimental design in a Scientific American article about 15 years ago. I have seen references to it since then but never researched it more extensivly. With my 2 years of college physics and a healthy interest in applies quantum phsyics hobbies, I would guess that after measurment the particle will have an increase in the level of randomness. In addition, the amount of energy will increase exponentially, increasing the entropy in the universe to compensate.
But IANAP and my guess should be taken with a large grain of salt.
Instead of wasting time developing this quantum nonsense, we need to find a way to send an avian carriers around the globe in the time it takes a photon to bounce off a satellite.