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Excited Atoms Advance Quantum Computing

By National Science Foundation

March 3, 2009

The dream of quantum computing has come a step closer to reality through National Science Foundation-funded research into atomic manipulation. Scientists led by University of Wisconsin-Madison professor Mark Saffman say they have demonstrated the use of a single atom to control another atom. They plan to use this technique to produce working logic devices that could eventually be incorporated into a quantum computer.

Saffman sought to create a CNOT gate that works with quantum bits (qubits), and he and colleague Thad Walker chose two neutral rubidium atoms to serve as qubits by cooling and trapping them 10 micrometers apart using a pair of laser beams. The atoms were then struck with laser pulses to "transition" electrons to high energy states, and these electrons can interact with each other across long distances, according to quantum mechanical theory.

"When two nearby Rydberg atoms get close enough, they affect each other," Saffman says. "This strong interaction changes their energy levels, preventing more than one atom at a time from being in a Rydberg state. So if one atom gets there first, no other atoms can join it." Saffman says this rule was proven by the experiment, and the next step will be to demonstrate an actual CNOT gate using the Rydberg blockade principle, and then scale up the system to work with a greater number of qubits.

From National Science Foundation
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