Magazine article Science News

Starting Up Quick Quantum Searches

Magazine article Science News

Starting Up Quick Quantum Searches

Article excerpt

Searching a telephone directory's alphabetical listings to match a given number with a name can be an onerous task. If you were unlucky, you might end up having to check every entry.

Using a conventional computer would speed up such a massive search considerably, but the task would probably still take a huge number of steps. A computer based on quantum mechanical principles, however, offers the theoretical possibility of performing certain computations and searches in significantly fewer steps (SN: 1/14/95, p. 30).

Now, researchers have for the first time demonstrated experimentally the operation of a simple quantum computer that can perform an efficient search, going all the way from a given initial state to the final answer in one step.

Isaac L. Chuang of the IBM Almaden Research Center in San Jose, Calif., Mark Kubinec of the University of California, Berkeley, and Neil A. Gershenfeld of the Massachusetts Institute of Technology describe their feat in the April 13 Physical Review Letters.

In a conventional computer, information can be stored and processed as strings of bits, each of which has one of two values, 0 or 1. Quantum computers deal with qubits--the quantum analogs of ordinary bits. Unlike bits, qubits are not confined to two states but can exist in a combination, or superposition, of states. That makes it possible to perform several logic operations simultaneously.

Mathematicians and computer scientists have proved that a quantum computer would require fewer steps than a conventional computer to perform certain mathematical operations, such as factoring whole numbers (SN: 5/14/94, p. …

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