Quantum Computing with Ions; August 2008; Scientific American Magazine; by Christopher R. Monroe and David J. Wineland; 8 Page(s)

Over the past several decades technological advances have dramatically boosted the speed and reliability of computers. Modern computer chips pack almost a billion transistors in a mere square inch of silicon, and in the future computer elements will shrink even more, approaching the size of individual molecules. At this level and smaller, computers may begin to look fundamentally different because their workings will be governed by quantum mechanics, the physical laws that explain the behavior of atoms and subatomic particles. The great promise of quantum computers is that they may be able to perform certain crucial tasks considerably faster than conventional computers can.

Perhaps the best known of these tasks is factoring a large number that is the product of two primes. Multiplying two primes is a simple job for computers, even if the numbers are hundreds of digits long, but the reverse process¿deriving the prime factors¿is so extraordinarily difficult that it has become the basis for nearly all forms of data encryption in use today, from Internet commerce to the transmission of state secrets. In 1994 Peter Shor, then at Bell Laboratories, showed that a quantum computer, in theory, could crack these encryption codes easily because it could factor numbers exponentially faster than any known classical algorithm could. And, in 1997, Lov K. Grover, also at Bell Labs, showed that a quantum computer could significantly increase the speed of searching an unsorted database¿say, finding a name in a phone book when you have only the person¿s phone number.