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Friday, June 08, 2007 New Record for Quantum CryptographyResearchers take a big step toward their goal of spy-proof communications via satellites. By Neil Savage
European scientists have broken a distance record for sending quantum information from one place to another, paving the way for a system that relies on the laws of physics to provide communications that can't be tapped. If they can extend the reach of their signal a little further, they'll be able to use satellites to send perfectly secure data around the world. The team used principles of quantum mechanics to create an encryption key in two locations simultaneously: one in a lab on La Palma, in the Canary Islands, and the second in an observatory on the neighboring island of Tenerife, 144 kilometers away. Such an encryption key can be used to encode data that only the sender and the receiver can decode. "We want to see whether it is possible at all to establish worldwide quantum communication, worldwide quantum cryptography," says Anton Zeilinger, a professor of physics at the Institute for Experimental Physics at the University of Vienna, Austria. His team, along with a team led by Harald Weinfurter of the Max Planck Institute of Quantum Optics, in Garching, Germany, published its results online on June 3 in the journal Nature Physics. To create the key, the team first had to create pairs of entangled photons. Entanglement, which Albert Einstein called "spooky action at a distance," means that the fate of one photon is tied up with the fate of the other. Measuring any quantum mechanical property of one photon automatically changes that same property in its entangled partner, no matter the distance between them. In this case, the team measured polarization. Light can be polarized in any direction; it's a measure of which direction the light waves are fluctuating in--horizontal or vertical, for example. Researchers created entangled pairs of photons by firing a powerful laser beam through a crystal. For each photon that went in, two weaker, entangled photons came out. The researchers bounced one half of each pair off a mirror to a local light detector on La Palma. They sent the other photon through a lens and out across the water, where a telescope on Tenerife caught it and sent it to a second light detector. "I have these two photons, and if I measure them on both ends and I ask them, 'Are you horizontally or vertically polarized?'--a binary choice--they will give a random answer," says Zeilinger. "But because of the entanglement, both will give the same answer. On both sides you get a zero or on both sides you get a one." Every time the detectors registered a photon and measured its polarization, that counted as a bit. A photon polarized in one direction was a one, and a photon polarized in the opposite direction was a zero. Add enough bits together, and you get an encryption key. And it's impossible to steal that key without the users' knowing about it. If someone were to intercept the flying photons , he could measure them himself, then send them on to the receiver. But the act of measuring them would change their quantum mechanical properties, so he'd be immediately exposed. |
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Quantum Leap
07/17/2008
Comments
brunascle on 06/08/2007 at 9:48 AM
Web Developer
70
measuring your photon does not change the entangled photon, in the normal sense of the word "change". that might imply that the entangled photon was a 1 before, but since you measured a 0 on your photon, the other one just changed to 0 as well. that's not what's happening. either both are 1 or both or 0, but you dont know which is the case yet.
the only weird part about this is that, in quantum mechanics, both of those 2 cases really do exist together until a measurement is made. both are 1 and both are 0 at the same time. when the measurement is made, 1 of those cases dissappears into nonexistence. which of the two is truly random.
the best explanation i've heard of this is the many words theory. before the measurement, two words blur together: one in which both are 1 and one in which both are 0. when the measurement is made, those 2 worlds split and can never interact again.
brunascle on 06/08/2007 at 9:55 AM
Web Developer
70
jim-frank on 06/08/2007 at 10:17 AM
1
blunney on 06/08/2007 at 2:51 PM
15
Science Jim on 06/08/2007 at 9:20 PM
1
If I have the intelligence and dollars so that I can tap into the system and read it in the first place then I would argue that I also have the intelligence, dollars, and equipment to create from scratch that what I had just read. It's not about continuing to pass along what I had just read, but rather stop what I had just read from continuing, and then recreating that from scratch and then putting that back into the flow stream to the final destination.
It seems straightforward to me. Am I missing something here? I'm not yet convinced that it is 100% impossible to tap / crack into it.
Your responses genuinely appreciated.
Jim
71LesPaul on 06/10/2007 at 12:33 AM
1
But if it payrolls research, so be it.
brunascle on 06/11/2007 at 2:45 PM
Web Developer
70
i understand why intercepting the message would screw up the communication between point A and point B, but i dont see would you couldnt do a man-in-the-middle attack and set up a new communication between the attacker and point B.
brunascle on 06/11/2007 at 3:06 PM
Web Developer
70
more info: http://en.wikipedia.org/wiki/Quantum_cryptography
kujospam on 06/09/2007 at 4:32 AM
1
ms on 06/09/2007 at 3:23 PM
65