at the National Institute of Standards and Technology
(NIST) have used charged atoms (ions) to demonstrate
a quantum physics version of computer memory lasting
longer than 10 seconds—more than 100,000
times longer than in previous experiments on the
same ions. The advance improves prospects for making
practical, reliable quantum computers (which make
use of the properties of quantum systems rather than
transistors for performing calculations or storing
information). Quantum computers, if they can be built,
could break today's best encryption systems, accelerate
database searching, develop novel products such as
fraud-proof digital signatures or simulate complex
biological systems to help design new drugs.
As described in the Aug. 5, 2005, issue of Physical
Review Letters ,* NIST scientists stored information
in single beryllium ions for longer periods of time
by using a different pair of the ions' internal energy
levels to represent 1 and 0 than was used in the
group's previous quantum computing experiments. This
new set of quantum states is unaffected by slight
variations in magnetic fields, which previously caused
memory losses in ions stored in electromagnetic traps.
memory must be able to store “superpositions,” an
unusual property of quantum physics in which a quantum
bit (qubit) such as an ion represents both 0 and
1 at the same time. The new approach enables qubits
to maintain superpositions over 1 million times longer
than might be needed to carry out the information
processing steps in a future quantum computer. The
advance is, therefore, an important step toward the
goal of designing a “fault tolerant” quantum computer
because it significantly reduces the computing resources
needed to correct memory errors.
related experiments also described in the paper,
NIST scientists demonstrated that pairs of “entangled” ions
can retain their quantum states for up to about 7
seconds. Entanglement is another unusual property
of quantum physics that correlates the behavior of
physically separated ions. Superposition and entanglement
are the two key properties expected to give quantum
computers great power.
The research was supported by the Advanced Research
and Development Activity/National Security Agency.
More information about NIST's quantum computing research
is available at http://qubit.nist.gov .
* C. Langer, R. Ozeri, J.D. Jost, J. Chiaverini,
B. DeMarco, A. Ben-Kish, R.B. Blakestad, J. Britton,
D.B. Hume, W.M. Itano, D. Leibfried, R. Reichle,
T. Rosenband, T. Schaetz, P.O. Schmidt and D. J.
Wineland. Long-lived qubit memory using atomic ions.
Physical Review Letters , 95, 060502 (2005).
Laura Ost, email@example.com , (301)