Alice and Bob are finally splitsville. After years of sending encrypted messages to each other, they're getting a divorce. They've moved away from each other and only communicate electronically, but this creates a problem. "They want to decide who's going to keep the dog, so they toss a coin," says Alipasha Vaziri, a physicist at the National Institute of Standards and Technology in Gaithersburg, Maryland. How to do a fair coin flip over a telephone wire? Physicists have now shown how, using quantum computers. In an upcoming issue of Physical Review Letters, Vaziri and his colleagues describe an experiment in which Alice and Bob perform a fair coin flip quantum-mechanically; if one party tries to cheat, the deception is quickly revealed, something that scientists don't know how to guarantee with classical computers.
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