Friday, July 2, 2010
Using a unique hybrid nanostructure, University of Maryland
researchers have shown a new type of light-matter interaction and
also demonstrated the first full quantum control of qubit spin
within very tiny colloidal nanostructures (a few nanometers), thus
taking a key step forward in efforts to create a quantum
computer.
Published in the July 1 issue of Nature,
their research builds on work by the same Maryland research team
published in March in the journal Science (3-26-10).
According to the authors and outside experts, the new findings
further advance the promise these new nanostructures hold for
quantum computing and for new, more efficient, energy generation
technologies (such as photovoltaic cells), as well as for other
technologies that are based on light-matter interactions like
biomarkers.
"The real breakthrough is that we use a new technology from
materials science to 'shed light' on light-matter interactions and
related quantum science in ways that we believe will have important
applications in many areas, particularly energy conversion and
storage and quantum computing," said lead researcher Min Ouyang, an
assistant professor in the department of physics and in the
university's Maryland NanoCenter. "In fact, our team already is
applying our new understanding of nanoscale light-matter
interactions and advancement of precise control of nanostructures
to the development of a new type of photovoltaic cell that we
expect to be significantly more efficient at converting light to
electricity than are current cells."
Ouyang and the other members of the University of Maryland team --
research scientist Jiatao Zhang, and students Kwan Lee and Yun Tang
-- have created a patent-pending process that uses chemical
thermodynamics to produce, in solution, a broad range of different
combination materials, each with a shell of structurally perfect
mono-crystal semiconductor around a metal core. In the research
published in this week's Nature, the researchers used hybrid
metal/semiconductor nanostructures developed through this process
to experimentally demonstrate "tunable resonant coupling" between a
plasmon (from metal core) and an exciton (from semiconductor
shell), with a resulting enhancement of the Optical Stark Effect.
This effect was discovered some 60 years ago in studies of the
interaction between light and atoms that showed light can be
applied to modify atomic quantum states.
Nanostructures, Large Advances
"Metal-semiconductor heteronanostructures have been investigated
intensely in the last few years with the metallic components used
as nanoscale antennas to couple light much more effectively into
and out of semiconductor nanoscale, light-emitters," said Garnett
W. Bryant, leader of the Quantum Processes and Metrology Group in
the Atomic Physics Division of the National Institute of Standards
and Technology (NIST). "The research led Min Ouyang shows that a
novel heteronanostructure with the semiconductor surrounding the
metallic nanoantenna can achieve the same goals. Such structures
are very simple and much easier to make than previously attempted,
greatly opening up possibilities for application. Most importantly,
they have demonstrated that the light/matter coupling can be
manipulated to achieve coherent quantum control of the
semiconductor nanoemitters, a key requirement for quantum
information processing," said Bryant, who is not involved with this
research. Bryant also is a scientist in the Joint Quantum
Institute, a leading center of quantum science research that is a
partnership between NIST and the University of Maryland.
Ouyang and his colleagues agree that their new findings were made
possible by their crystal-metal hybrid nanostructures, which offer
a number of benefits over the epitaxial structures used for
previous work. Epitaxy has been the principle way to create single
crystal semiconductors and related devices. The new research
highlights the new capabilities of these UM nanostructures, made
with a process that avoids two key constraints of epitaxy -- a
limit on deposition semiconductor layer thickness and a rigid
requirement for "lattice matching."
The Maryland scientists note that, in addition to the enhanced
capabilities of their hybrid nanostructures, the method for
producing them doesn't require a clean room facility and the
materials don't have to be formed in a vacuum, the way those made
by conventional epitaxy do. "Thus it also would be much simpler and
cheaper for companies to mass produce products based on our hybrid
nanostructures," Ouyang said.
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University of Maryland
Thanks to University of Maryland
for this article.