How to build a super fast computer that uses the bizarre properties of quantum physics is the aim of a project by computer scientists Fred Chong of the University of California, Davis, Isaac Chuang at MIT and John Kubiatowicz at UC Berkeley. The five-year project is supported by a grant of $3 million from the Defense Advanced Research Projects Agency. The grant will establish a Quantum Architecture Research Center between MIT, UC Davis and UC Berkeley.
A quantum computer could solve problems in a few months that would take conventional computers millions of years, Chong said.
Quantum physics describes the special rules that apply to atoms and subatomic particles. One principle is that when you observe a particle, you change it. If a particle can be in one of two states, for example "up" or "down," it only settles on one state when you look at it. Before you look at it, it can be in both states at the same time.
Conventional computers process information as "bits." A bit can be a one or a zero. A string of eight bits can represent a single number from zero (00000000) to 255 (11111111). In a quantum computer, bits can be both one and zero at the same time. A string of eight bits can therefore represent all of the numbers between zero and 255 at the same time.
Quantum computers would be able to do some types of calculations much faster than conventional computers, said Chong. For example, public key encryption, widely used on the Internet, creates codes by multiplying two prime numbers together. Multiplying two primes is easy, but working backward from the product to the two prime numbers is extremely hard. That makes the codes very hard to break.
For a large key, a conventional computer could take millions of years to work through all the possible solutions to find the right one, Chong said. A quantum computer would solve it in about a month, because it can look at many solutions at the same time.
Quantum computers could also take advantage of another quantum property, teleportation. Teleportation allows information about one particle to be transmitted to another particle some distance away. A quantum computer could use teleportation instead of wires to move bits around inside itself.
Simple quantum computers have already been built, for example by Chuang and Neil Gershenfeld at MIT. Their machine uses molecules in solution to carry bits of information and uses a nuclear magnetic resonance (NMR) machine to manipulate them and read out the results. The DARPA project would focus on working out the design principles of more powerful computers, Chong said.
The center also plans to collaborate with the Quantum Science Research Group at Hewlett-Packard, Chong said.
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