Stanford University physicist Thaddeus Ladd clarifies misconceptions about quantum computers: The futuristic devices will actually be slower than today’s transistor-based computers. They will have less storage capacity and will probably never be used as PCs. So what’s the big deal with quantum computers?

"Their promise is that they are able to perform algorithms that classical computers simply cannot perform," says Ladd. "Superpositions [of 0’s and 1’s] could allow a quantum computer to beat IBM’s Blue Gene and other supercomputers at certain problems, such as factoring large numbers, because it ‘cheats’ in the race, or takes a shortcut."

Ladd, who also works at the National Institute of Informatics in Tokyo, is a member of a team led by Yoshihisa Yamamoto that recently designed a potentially scalable quantum computing scheme in which many quantum bits, or qubits, can be added at once. In its "loop qubus," a laser changes the spin of electrons (which act as qubits) held in a loop of quantum dots. For schemes with more than a few bits, the qubus is the fastest design to date.

"The qubus scheme is a way of ‘busing’ information from one qubit to another—thus the name qubit-bus, shortened to qubus—using a pulse of light," explains Susan M. Clark, lead author of the team’s recent paper in Physical Review Letters ( 2007).

The team expects to publish ideas soon about how the technology might actually be implemented, with real numbers for speed and cost.

See a diagram on how quantum computing works.