Computers can become zillions of times faster

August 21st, 2008 - 3:57 pm ICT by IANS  

New York, Aug 21 (IANS) The fastest quantum computer bit or the qubit has been shown to be zillions of times faster than the conventional bit, potentially making computers that much faster. Scientists used lasers to create an initialised quantum state of this solid-state qubit at rates of about a gigahertz, or a billion times per second.

A conventional bit can be a 0 or a 1 but a qubit can be both at the same time. Until now, scientists couldn’t stabilise that duality.

Because of their ability to represent multiple states simultaneously, quantum computers could theoretically make calculations dramatically faster and with much smaller computers. Consequently, they could vastly improve computer security.

Duncan Steel, a physics professor, doctoral student Xiaodong Xu and their colleagues used lasers to trap the spin of one electron confined in a single semiconductor quantum dot. A quantum dot is like a transistor in a conventional computer.

“We are the first to show that you can do this to a single electron in a self-assembled quantum dot,” Steel said. “If you’re going to do quantum computing, you have to be able to work with one electron at a time.”

The scientists trapped the spin in a dark state where they can arbitrarily adjust the amount of 0 and 1 the qubit represents. They call this state “dark” because it does not absorb light. In other words, the light does not destabilise the qubit.

Spin is an intrinsic property of the electron which Steel compares with magnetic poles. Electrons are said to have spin up or down. In quantum computing, the up and down directions represent the 0s and 1s of conventional computing.

Steel’s approach to developing a quantum computer is to use ultrafast lasers to manipulate arrays of semiconductor quantum dots, each containing one electron. Quantum logic gates are formed by quantum mechanical interactions between the dots.

Previously in Steel’s lab, researchers have used a laser to produce an electron in a state representative of a 1 or a 0 and a small amount of the other state. Now, using two laser frequencies, they have trapped it as a 0 and a 1 at the same time, and they can adjust the amount of each.

“The National Security Agency has said that based on our present technology, we have about a 20-year window of security,” Steel said.

“That means if we sent up a satellite today, it would take somebody about 20 years to crack the code. Quantum computers will let you develop a code that would be impossible to crack with a conventional computer.”

These findings are scheduled for publication in Nature Physics and are available in the online edition.

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