Atom demo fixes quantum errors

Although quantum computers promise fantastic speed for certain types of very large problems, the logical components of quantum computers -- quantum bits -- are quite fragile, which makes for a large number of errors that must be corrected.

Researchers from the National Institute of Standards and Technology have demonstrated a way to correct errors in qubits of beryllium ions held in an electromagnetic trap. The ions represent a 1 or 0 of computer information in their spin, which can be pictured as the counterclockwise or clockwise spin of a top.

One way to carry out quantum computing is to take advantage of a weird trait of quantum particles -- they can become entangled, or linked, so that properties like spin remain in lockstep.

The researchers' prototype uses lasers to control the qubits' states and electrodes to move them together, which allows them to be entangled. The researchers set a primary qubit to a particular state and entangled it with two other qubits. They deliberately induced an error and then disentangled the qubits by separating them.

They measured the other two qubits to determine how the primary qubit needed to be corrected.

Quantum error correction schemes have been well explored theoretically, but the researchers' experiment was the first demonstration of a repeatable error-correction procedure and the first using trapped ions, which are a promising candidate for practical quantum computers.

Practical quantum computing is a decade or more away. The method could be used in quantum communications applications like quantum cryptography within a few years, according to the researchers. The work appeared in the December 2, 2004 issue of Nature.