Physicists extend the quantum lifetime of electrons

November 17, 2008: Physicists in the USA and at the London Centre for Nanotechnology have found a way to extend the quantum lifetime of electrons by more than 5000%, as reported in the Nov. 14 edition of Physical Review Letters.

Electrons exhibit a property called ‘spin’ and work like tiny magnets which can point up, down or a quantum superposition of both. The state of the spin can be used to store information and so by extending their life the research provides a significant step towards building a usable quantum computer.

“Silicon has dominated the computing industry for decades,” says Dr. Gavin Morley, lead author of the paper. “The most sensitive way to see the quantum behavior of electrons held in silicon chips uses electrical currents. Unfortunately, the problem has always been that these currents damage the quantum features under study, degrading their usefulness.”

Marshall Stoneham, professor of physics at University College London (UCL), commented: “Getting the answer from a quantum computation isn’t easy. This new work takes us closer to solving the problem by showing how we might read out the state of electron spins in a silicon-based quantum computer.”

To achieve the record quantum lifetime the team used a magnetic field 25× stronger than those used in previous experiments. This powerful field also provided an additional advantage in the quest for practical quantum computing — it put the electron spins into a convenient starting state by aligning them all in one direction.

Microwaves are used to control the spin state of electrons held in silicon. This spin state can be watched in real time by measuring the electric current flowing between the (gray) electrodes. (Credit: UCL/London Centre for Nanotechnology)


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