Haven for Quantum Computation

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Science  01 Sep 2000:
Vol. 289, Issue 5484, pp. 1433
DOI: 10.1126/science.289.5484.1433b

Their potential for solving difficult problems that classical computers cannot, and doing so more quickly, has generated much interest in the development of quantum computers. Just as a noisy environment can break our train of thought, the manipulation of a quantum state can result in its being disturbed or lost during interactions with its own environment—a process known as decoherence. Quantum error correction, in which code words placed in the message tell us how much the system has been distorted, works well for recovering the lost information but exacts a heavy computational cost.

In a decoherence-free subspace (DFS), fragile quantum states are protected from noisy surroundings. However, it was thought that useful calculations requiring manipulation of the quantum state would require moving out of this protected environment. Now, two approaches have been proposed that show that quantum calculations can be performed without the need to leave the DFS. Bacon et al. describe a scheme for performing a calculation while staying within the DFS. Beige et al. utilize the Zeno effect, the quantum-mechanical equivalent to soccer's juggling the ball, to maintain the system in a DFS while the calculation takes place. Both approaches should be particularly useful for solid-state implementations of quantum computers. — ISO

Phys. Rev. Lett.85, 1758 (2000); Phys. Rev. Lett.85, 1762 (2000).

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