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Keeping the "noise" down

Physics professor covers new ground in quantum computation quest
Lorenza Viola
Lorenza Viola

Associate Professor of Physics and Astronomy Lorenza Viola is among a group of physicists throughout the nation and the world who are working to make highly-theoretical quantum-mechanical computers a reality. Quantum computation deals with the smallest of the small; information is measured on an atomic scale, and unlike classical computing in which every value is either a one or a zero, quantum bits ("qubits") are capable of existing in a continuous superposition of values, which makes the potential for error nearly infinite. That's why Viola's recent publication, "Experimental Implementation of a Concatenated Quantum Error-Correcting Code," published in the April issue of Physical Review Letters is an important step forward in the field.

Using computations and network maps that read like an alien language to non-physicists, Viola and her co-authors conducted an experiment on four spinning nuclei in a solution of crotonic acid. The nuclei are subject to undesired interference effects from external degrees of freedom, a phenomenon known as "quantum noise" in physics jargon. Viola's experiment attempted to counteract the effects of that noise by creating a "concatenated," or hierarchical error-correcting code, greatly reducing the impact of errors in the system.  According to Viola, concatenated codes can tolerate more realistic types of errors than standard ones and are regarded as a critical ingredient for realizing so-called "quantum fault-tolerance."

Ultimately, this strategy could point the way toward real-life quantum processing which will have profound implications for performing critical mathematical tasks, such as database searching and number factoring and for simulating complex quantum systems.

The experiment was carried out at the MIT Spatial NMR Laboratory, in collaboration with a team led by David G. Cory, Professor of Nuclear Engineering at MIT.

By GENEVIEVE HAAS

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Last Updated: 12/17/08