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

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.


More information:

Media contacts:

— Fred Chong, Computer Science, 530-754-9510,