Artificial atoms or Quantum dots.
Artificial atom is an object that has bound, discrete electronic states, as is the case with naturally occurring atoms. Semiconductor
quantum dots are the most common example of artificial atoms, and are analogies for real atoms. Artificial atoms are made up of more than
one atom, but are like single atoms in one important way: when you
provide the right amount (or quanta) of energy, they will give off
coloured light.
Programmable matter refers to matter which has the ability to change its physical properties (shape, density,
moduli,
optical properties, etc.) in a programmable fashion, based upon user
input or autonomous sensing. Programmable matter is thus linked to the
concept of a material which inherently has the ability to perform
information processing.
.
Programmable matter is a term originally coined in 1991 by Toffoli and Margolus to refer to an ensemble of fine-grained computing elements arranged in space. Their paper describes a computing substrate
that is composed of fine-grained compute nodes distributed throughout
space which communicate using only nearest neighbor interactions. In
this context, programmable matter refers to compute models similar to cellular automata and Lattice Gas Automata. The CAM-8 architecture is an example hardware realization of this model. This function is also known as "digital referenced areas" (DRA) in some forms of self-replicating machine science.
1. The programming could be external to the material and might be achieved
by the "
application of light, voltage, electric or magnetic fields, etc.". For example, in this school of thought, a
liquid crystal display is a form of programmable matter.
2. The individual units of the ensemble can compute and the result of
their computation is a change in the ensemble's physical properties.
3. Scale is one key differentiator between different forms of programmable matter. Nano - cm, and even bigger. At the nanoscale end of the spectrum there are a tremendous number of
different bases for programmable matter, ranging from shape changing
molecules
to
quantum dots or artificial atoms. In the
micrometer to sub-millimeter range examples include claytronics,
MEMS-based units, cells created using
synthetic biology, and the
utility fog concept.
"Simple" programmable matter see also Smart material.
Materials that can change their properties based on some input, but do
not have the ability to do complex computation by themselves.
1. The physical properties of several
complex fluids can be modified by applying a current or voltage, as is the case with
liquid crystals.
2.
Metamaterials are artificial
composites
that can be controlled to react in ways that do not occur in nature.
One example developed by David Smith and then by John Pendry and David
Schuri is of a material that can have its
index of refraction tuned so that it can have a different index of refraction at different points in the material.
3.
Molecules that can change (mechanostereochemistry) their shape, as well as other properties, in response to external stimuli. Can be used individually or en masse, ex, molecules that can
change their electrical properties as mechanized molecules, mechanically-interlocked molecular architectures such as
molecular Borromean rings,
catenanes and
rotaxanes utilizing
molecular recognition and
molecular self-assembly
processes. These topologies can be employed as
molecular switches and as motor-molecules, and even applied
these structures in the fabrication of nanoelectronic devices and
nanoelectromechanical systems (NEMS).
π–stack charachters have been applied to the DNA structure too, as reductive electron-transport system, and its oxidative hairpins for hole transfer through DNA. These interactions are important in base stacking of DNA nucleotides,
protein folding and protein chrystal formation, template-directed synthesis, materials science, and
molecular recognition, Despite intense experimental and theoretical interest, there is no
unified description of the factors that contribute to pi stacking
interactions. There are compelling computational evidence for the importance of direct interaction in pi stacking. It seems that the relative contributions of electrostatics,
dispersion, and direct interactions to the substituent effects seen in
pi stacking interactions
are highly dependent on geometry and
experimental design. The
chromophore has also a special role, and it has been linked to quantum biology. see
Mechanisms for DNA charge transport..
Self-Reconfiguring Modular Robotics is a field of robotics in which a
group of basic robot modules work together to dynamically form shapes
and create behaviours suitable for many tasks. Like Programmable matter
SRCMR aims to offer significant improvement to any kind of objects or
system by introducing many new possibilities for example:
1. Most
important is the incredible flexibility that comes from the ability to
change the physical structure and behavior of a solution by changing the
software that controls modules.
2. The ability to self-repair by
automatically replacing a broken module will make SRCMR solution
incredibly resilient.
3. Reducing the environmental foot print by
reusing the same modules in many different solutions.
Claytronics, nanoscale robots ('claytronic
atoms', or
catoms) designed to form much larger scale
machines
or mechanisms. The catoms will be sub-millimeter computers that will
eventually have the ability to move around, communicate with other
computers, change color, and
electrostatically connect to other catoms to form different shapes.
Quantum wells, a
potential well with only discrete energy values, can hold one or more electrons. Those electrons behave like
artificial atoms which, like real atoms, can form
covalent bonds, but these are extremely weak. Because of their larger sizes, other properties are also widely different. One way to create
quantization is to confine particles, which were originally
free to move in three dimensions, to two dimensions, forcing them to
occupy a planar region. The effects of
quantum confinement take place when the quantum well thickness becomes comparable to the
de Broglie wavelength of the carriers (generally
electrons and
holes), leading to energy levels called "energy subbands", i.e., the carriers can only have discrete energy values. Quantum wells are formed in semiconductors by having a material, like
gallium arsenide sandwiched between two layers of a material with a wider
bandgap, like
aluminium arsenide. These structures can be grown by
molecular beam epitaxy or
chemical vapor deposition with control of the layer thickness down to
monolayers. Thin metal films can also support quantum well states, in particular,
metallic thin overlayers grown in metal and semiconductor surfaces. The
electron (or hole) is confined by the vacuum-metal interface in one
side, and in general, by an absolute gap with semiconductor substrates,
or by a projected band gap with metal substrates.
Synthetic biology aims to engineer cells with "novel biological functions." Such cells are
usually used to create larger systems (e.g., biofilms) which can be
"programmed" utilizing synthetic gene networks such as
genetic toggle switches, to change their color, shape, etc.
Protocells and other minimal solutions.
Construction of a chemical system capable of replication and evolution,
fed only by small molecule nutrients, is now conceivable. This could be
achieved by stepwise integration of decades of work on the
reconstitution of DNA, RNA and protein syntheses from pure components.
Such a minimal cell project would initially define the components
sufficient for each subsystem, allow detailed kinetic analyses and lead
to improved in vitro methods for synthesis of biopolymers,
therapeutics and biosensors. Completion would yield a functionally and
structurally understood self-replicating biosystem. Safety concerns for
synthetic life will be alleviated by extreme dependence on elaborate
laboratory reagents and conditions for viability. Our proposed minimal
genome is 113 kbp long and contains 151 genes. We detail building blocks
already in place and major hurdles to overcome for completion.
A minimal cell containing biological macromolecules and pathways proposed to be
necessary and sufficient for replication from small molecule nutrients.
See also
Quantum dots are like man-made, detected 1980,
artificial atoms that are described by discrete states.
It is a portion of matter (e.g.,
semiconductor) whose
excitons are
confined in all three
spatial dimensions.
Consequently, such materials have electronic properties intermediate
between those of bulk semiconductors and those of discrete
molecules. They could only be used in low temperature settings earlie, but this new technology described in
Science Daily does not. Quantum dots have previously ranged in size from 2-10 nanometers in
diameter. While typically composed of several thousand atoms, all the
atoms pool their electrons to “sing with one voice”, that is, the
electrons are shared and coordinated as if there is only one atomic
nucleus at the centre.
As with any crystalline semiconductor, a quantum dot's electronic
wave functions extend over the
crystal lattice. Similar to a molecule, a quantum dot has both a
quantized energy
spectrum and a quantized
density of electronic states near the edge of the band gap. The quantum dot absorption features correspond to transitions between discrete,three-dimensional
particle in a box states of the
electron and the hole, both confined to the same
nanometer-size box.These discrete transitions are reminiscent of atomic spectra and have resulted in quantum dots also being called
artificial atoms.
Its electronic characteristics are closely related to the size and shape of
the individual crystal. Generally, the smaller the size of the crystal,
the larger the
band gap, the greater the difference in energy between the highest
valence band and the lowest
conduction band
becomes, therefore more energy is needed to excite the dot, and
concurrently, more energy is released when the crystal returns to its
resting state. A main advantage with quantum dots is that, because of the high level
of control possible over the size of the crystals produced, it is
possible to have very precise control over the conductive properties of
the material.
Quantum dots of different sizes can be assembled into a
gradient multi-layer nanofilm.
The National Institute of Nanotechnology at the University of Alberta announced that they created the smallest quantum dot, 2009. From
What's the spin on quantum dots.
In a semiconductor crystal lattice, the electrons are squeezed together,
since no two nearby electrons can share exactly the same energy level
according to
Pauli exclusion principle, leading to
quantum confinement. The energy level can then be modeled using
particle in a box,
which leads to the conclusion that the energy levels of the quantum dot
is dependent on its size. When the size of the quantum dot is smaller
than the critical characteristic length called the
Exciton Bohr radius,
the electrons crowding lead to the splitting of the original energy
levels into smaller ones with smaller gaps between each successive
level. The Exciton Bohr radius is larger than the Bohr radius due to the
effect of dielectric screening and the influence of periodic lattice
structure of the crystal. The quantum dots that have radii larger than
the Exciton Bohr radius are said to be in the 'weak confinement regime'
and the ones that have radii smaller than the Exciton Bohr radius are
said to be in the 'strong confinement regime'. Thus, if the size of the
quantum dot is small enough that the quantum confinement effects
dominate(typically less than 10 nm), the electronic and optical
properties change, and the fluorescent wavelength is determined by the
size.
3D confined electron wave functions in a quantum dot. Here, rectangular
and triangular-shaped quantum dots are shown. Energy states in
rectangular dots are more s-type and p-type. However, in a triangular dot the wave functions are mixed due to confinement symmetry.
Besides confinement in all three dimensions (i.e., a quantum dot), other quantum confined semiconductors include:
- Quantum wires, which confine electrons or holes in two spatial dimensions and allow free propagation in the third.
- Quantum wells, which confine electrons or holes in one dimension and allow free propagation in two dimensions. Wells can be of many kinds.
Different sized quantum dots emit different color light due to quantum confinement.
The images in
this series represent
the electron densities in a quantum dot artificial
atom.
Quantum Dot Wave Function (
Image 1)
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The visuals were generated by the nanoelectronic modeling tool called
NENO 3-D, and were visualized on the nanoVIS rendering service at
www.nanoHUB.org, a rich, Web-based resource for research, education and
collaboration in nanotechnology.
NanoHUB.org was created by the National Science Foundation (NSF)-funded
Network for Computational Nanotechnology (NCN), a network of
universities with a vision to pioneer the development of nanotechnology,
from science to manufacturing, through innovative theory, exploratory
simulation and novel cyberinfrastructure. NCN students, staff and
faculty are developing the NanoHUB science gateway, while making use of
it in their own research and education. Collaborators and partners
across the world have joined NCN in this effort.
NanoHUB hosts over 790 resources to help users learn about
nanotechnology, including online presentations, courses, learning
modules, podcasts, animations, teaching materials and more. Most
importantly, NanoHUB offers simulation tools that can be accessed from
your Web browser, so you can not only learn about, but also simulate
nanotechnology devices. NanoHUB also provides collaboration environment
via Workspaces, online meetings and user groups.
(Date of Image: May 2006) Image 2.
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|
Image 3
Credit:
Wei Qiao, David Ebert, Marek Korkusinski, Gerhard Klimeck; Network for Computational Nanotechnology, Purdue University
Download the high-resolution JPG version of the image. (399 KB |
Use your mouse to right-click (Mac users may need to
Ctrl-click) the link above and choose the option that will save the file
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Synthetic chrystals.
Element Six, the world leader in synthetic
diamond supermaterials, working in partnership with academics in Harvard
University, California Institute of Technology and Max-Planck-Institut
für Quantenoptik, has used its Element Six single crystal synthetic diamond grown by chemical vapour deposition (CVD) to demonstrate the
capability of quantum bit memory to exceed one second at room
temperature.
Using synthetic diamond, Element Six and Harvard University have set a
new room temperature quantum information storage record of more than one
second – a thousand times longer than previously recorded.
It proved the ability of synthetic diamond to
provide the read-out of a quantum bit which had preserved its spin
polarisation for several minutes and its memory coherence for over a
second. This is the first time that such long memory times have been
reported for a material at room temperature, giving synthetic diamond a
significant advantage over rival materials and technologies that require
complex infrastructure which necessitates, for example, cryogenic
cooling.
The versatility, robustness, and potential scalability of
this synthetic diamond system may allow for new applications in quantum
information science and quantum based sensors used, for example, in
nano-scale imaging of chemical/biological processes.
Steve Coe, Element Six Group Innovation Director,
explained the success of the collaboration:
"The field of
synthetic diamond science is moving very quickly and is requiring
Element Six to develop synthesis processes with impurity control at the
level of parts per trillion – real nano-engineering control of CVD
diamond synthesis. We have been working closely with Professor Lukin's
team in Harvard for three years - this result published in Science is an
example of how successful this collaboration has been."
Professor Mikhail Lukin of Harvard University's Department of Physics described the significance of the research findings:
"Element Six's unique and engineered synthetic diamond material has
been at the heart of these important developments. The demonstration of a
single qubit quantum memory with seconds of storage time at room
temperature is a very exciting development, which combines the four key
requirements of initialisation, memory, control and measurement. These
findings might one day lead to novel quantum communication and
computation technologies, but in the nearer term may enable a range of
novel and disruptive quantum sensor technologies, such as those being
targeted to image magnetic fields on the nano-scale for use in imaging
chemical and biological processes."
The findings represent the
latest developments in quantum information processing, which involves
manipulating individual atomic sized impurities in synthetic diamond and
exploiting the quantum property spin of an individual electron, with superposition so this quantum spin (qubit) can be both 0 and 1
simultaneously. It is this property that provides a framework for
quantum computing, but also for more immediate applications such as
novel magnetic sensing technologies.
See also
About protons and atoms.