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.
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