Physicists Create First Long-Distance Quantum Link_Featured_, Quantum Physics, Technology Monday, April 16th, 2012
(Wired) For more than a decade, physicists have been developing quantum mechanical methods to pass secret messages without fear that they could be intercepted. But they still haven’t created a true quantum network — the fully quantum-mechanical analog to an ordinary telecommunications network in which an uncrackable connection can be forged between any two stations or “nodes” in a network. Now, a team of researchers in Germany has built the first true quantum link using two widely separate atoms. A complete network could be constructed by combining many such links, the researchers say.
“These results are a remarkable achievement”, says Andrew Shields, applied physicist and assistant managing director at Toshiba Research Europe Ltd. in Cambridge, U.K., who was not involved in the work. “In the past we have built networks that can communicate quantum information, but convert it into classical form at the network switching points. [The researchers] report preliminary experiments towards forming a network in which the information remains in quantum form.”
Quantum communications schemes generally take advantage of the fact that, according to quantum theory, it’s impossible to measure the condition or “state” of a quantum particle without disturbing the particle. For example, suppose Alice wants to send Bob a secret message. She can do the encrypting in a traditional way, by writing out the message in the form of a long binary number and zippering it together in a certain mathematical way with a “key,” another long stream of random 0s and 1s. Bob can then use the same key to unscramble the message.
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Image: Andreas Neuzner/Max Planck Institute of Quantum Optics