Внятная статья о квантовых эффектах в "Wall Street Journal" (англ.)

[wayter]

http://online.wsj.com/article/SB124147752556985009.html


Last year, Dr. Gisin and colleagues at Geneva University described how they had entangled a pair of photons in their lab. They then fired them, along fiber-optic cables of exactly equal length, to two Swiss villages some 11 miles apart.

During the journey, when one photon switched to a slightly higher energy level, its twin instantly switched to a slightly lower one. But the sum of the energies stayed constant, proving that the photons remained entangled.

More important, the team couldn't detect any time difference in the changes. "If there was any communication, it would have to have been at least 10,000 times the speed of light," says Dr. Gisin. "Because this is such an unlikely speed, the conclusion is there couldn't have been communication and so there is non-locality."

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In 1990, the English physicist Lucien Hardy devised a thought experiment. The common view was that when a particle met its antiparticle, the pair destroyed each other in an explosion. But Mr. Hardy noted that in some cases when the particles' interaction wasn't observed, they wouldn't annihilate each other. The paradox: Because the interaction had to remain unseen, it couldn't be confirmed.

In a striking achievement, scientists from Osaka University have resolved the paradox. They used extremely weak measurements -- the equivalent of a sidelong glance, as it were -- that didn't disturb the photons' state. By doing the experiment multiple times and pooling those weak measurements, they got enough good data to show that the particles didn't annihilate. The conclusion: When the particles weren't observed, they behaved differently.

In a paper published in the New Journal of Physics in March, the Japanese team acknowledged that their result was "preposterous." Yet, they noted, it "gives us new insights into the spooky nature of quantum mechanics." A team from the University of Toronto published similar results in January.

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When encrypting sensitive data such as a bank transfer, both the sending party and the receiving party must have the same key. The sender needs the key to hide the message and the receiver to reveal it. Since it isn't always practical to exchange keys in person, the key must be sent electronically, too. This means the key (and the messages) may be intercepted and read by an eavesdropper.

An electronic key is usually written in the computer binary code of "ones" and "zeros." Quantum physics permits a more sophisticated approach. The same "ones" and "zeros" can now be encoded by using the properties of photons, like spin. If someone intercepts a photon-based message, the spins change. The receiver then knows the key has been compromised.


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Because of its bizarre implications, quantum theory has been used to investigate everything from free will and the paranormal to the enigma of consciousness.