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 5,000 per cent, as reported recently in 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.
 | | 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 (grey) electrodes. (Credit: Image courtesy UCL) |
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 behaviour 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 UCL (University College London),
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 twenty-five
times 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.
For more information, see the paper published in Physical Review Letters, November
14 2008, by G. W. Morley (London Center for Nanotechnology), D. R. McCamey (University
of Utah), H. A. Seipel (University of Utah), L.-C. Brunel (National High Magnetic
field Laboratory), J. van Tol (National High Magnetic field Laboratory) and
C. Boehme (University of Utah).
Posted November 15th, 2008
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