Researchers from the University of Twente
in the Netherlands have showed that the spacing of a photonic crystal
can be used to control the timing of light emitted by a quantum dot.
Photonic crystals are lattice-like materials made from solids
perforated with holes or from regularly-spaced rods or spheres. A quantum
dot is a minuscule speck of semiconductor material.
The method could be used to make smaller, more efficient miniature
lasers and light-emitting diodes by accelerating light emission, and more
efficient solar cells by slowing emission, according to the researchers.
And it could eventually be used to shield the fragile quantum information
contained in quantum computers.
The researchers placed 4.5-nanometer cadmium selenide quantum
dots inside photonic crystal cavities that were 240 to 650 nanometers
across and excited the quantum dots with laser pulses that lasted only
a few trillionths of a second. The laser energy caused the quantum dots
to emit light at a rate that depended on the spacing of the photonic crystals,
with wider spacings yielding higher-intensity emissions. A nanometer is
one millionth of a millimeter.
Photonic crystals can simultaneously control many light wavelengths,
The researchers are working on a photonic crystal laser. A prototype
is possible within a year, and commercial lasers could be ready in five
years, according to the researchers. It will be five to ten years before
the method can be used in solar cells, according to the researchers. Researchers
generally agree that quantum computers are 10 to 20 years away.
The work appeared in the August 5, 2004 issue of Nature.
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