Scientists protect quantum information in a noiseless subsystem

Contact: Todd Hanson, tahanson@lanl.gov, (505) 665-2085

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LOS ALAMOS, N.M., Sept. 14, 2001 -- Theorists at the Department of Energy's Los Alamos National Laboratory, in collaboration with an experimental team at the Massachusetts Institute of Technology, have realized a general and efficient method for protecting quantum information against noise. The demonstration paves the way for the development of novel means for storing delicate quantum information and should, in turn, further the evolution of quantum computers. Quantum computers promise greatly increased computational speeds useful for performing critical mathematical tasks, such as database searching and number factoring, and for simulating complex quantum systems.

In a paper that appears in the today's issue of Science magazine, Los Alamos researcher Lorenza Viola, Evan M. Fortunato of MIT and their colleagues describe the encoding of quantum information in a physical degree of freedom protected against noise - something scientists call a "noiseless subsystem" - using nuclear magnetic resonance on molecules of the amino acid alanine. Achieving noise control is indispensable for quantum information processing. Noiseless subsystems are immune to certain types of information-corrupting "noise," which could otherwise disrupt computations that exploit fragile quantum states.

"Previous Los Alamos and MIT research has shown that noiseless subsystems exist whenever a symmetry occurs in the noise. Noiseless subsystems conceptually unify the ways we think of noise control. In addition, we know that it is possible in principle to perform quantum computations without leaving the noise-protected system," said Viola. "Our results are the first experimental step confirming that general theory, and will hopefully motivate other quantum researchers to explore practical implications of noiseless subsystems for quantum information storage and manipulation."

Los Alamos National Laboratory has been a leader in theoretical and experimental quantum computation since quantum computers were first proposed in the early 1990s.

Quantum researchers use qubits, or quantum bits, as a basic unit of information and the counterpart to the binary bit in classical computing. A three-qubit quantum device was demonstrated at Los Alamos in 1998 and in early 2000 researchers built the first seven-qubit device. This demonstration comes on the heels of last year's work by Knill, Laflamme, and Viola where the notion of a "noiseless subsystem" was first discovered.

Viola and her colleagues are part of a collective effort at Los Alamos working in areas of quantum information processing and related fields like quantum cryptography. Work on noiseless subsystems was funded by the Los Alamos postdoctoral program, Laboratory Directed Research and Development and the National Security Agency.

Besides Viola, the Los Alamos team included Emanuel Knill and Raymond Laflamme. The MIT team also included Marco A. Pravia and David G. Cory.

Los Alamos National Laboratory is operated by the University of California for the U.S. Department of Energy's National Nuclear Security Administration.