Large quantum computers could in principle handle some of the toughest computing problems, such as factoring numbers to break encrypted messages--answering those questions in seconds instead of the centuries that today's computers would require. But quantum computers are extraordinarily difficult to build; they rely on exquisitely controlled interactions among fragile quantum states. Do they have to? Recently Ian A. Walmsley and his co-workers at the University of Rochester demonstrated that ordinary, classical light waves can perform as efficiently as one class of quantum computer.

The Rochester experiment searched a sorted 50-element database. An ordinary computer doing a binary search of such a database would need to query the database six times (enough to search 64 elements: 26 = 64). In 1997 Lov K. Grover of Bell Laboratories proved that a quantum computer only has to query once, no matter how large the database.

This article was originally published with the title Computing with Light.

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