Physicists at the National Institute of Standards and Technology (NIST)have used charged atoms (ions) to demonstrate a quantum physics versionof computer memory lasting longer than 10 seconds--more than 100,000times longer than in previous experiments on the same ions. The advanceimproves prospects for making practical, reliable quantum computers(which make use of the properties of quantum systems rather thantransistors for performing calculations or storing information).Quantum computers, if they can be built, could break today's bestencryption systems, accelerate database searching, develop novelproducts such as fraud-proof digital signatures or simulate complexbiological 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 longerperiods of time by using a different pair of the ions' internal energylevels to represent 1 and 0 than was used in the group's previousquantum computing experiments. This new set of quantum states isunaffected by slight variations in magnetic fields, which previouslycaused memory losses in ions stored in electromagnetic traps.
Quantum memory must be able to store "superpositions," an unusualproperty of quantum physics in which a quantum bit (qubit) such as anion represents both 0 and 1 at the same time. The new approach enablesqubits to maintain superpositions over 1 million times longer thanmight be needed to carry out the information processing steps in afuture quantum computer. The advance is, therefore, an important steptoward the goal of designing a "fault tolerant" quantum computerbecause it significantly reduces the computing resources needed tocorrect memory errors.
In related experiments also described in the paper, NIST scientistsdemonstrated that pairs of "entangled" ions can retain their quantumstates for up to about 7 seconds. Entanglement is another unusualproperty of quantum physics that correlates the behavior of physicallyseparated ions. Superposition and entanglement are the two keyproperties expected to give quantum computers great power.
The research was supportedby the Advanced Research and Development Activity/National SecurityAgency. More information about NIST's quantum computing research isavailable 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).
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