an invisible technology
a scientific pursuit, the search for a viable successor to silicon computer technology
has garnered considerable curiosity in the last decade. The latest idea, and one
of the most intriguing, is known as molecular computers, or moletronics, in which
single molecules serve as switches, "quantum wires" a few atoms thick
serve as wiring, and the hardware is synthesized chemically from the bottom up.
central thesis of moletronics is that almost any chemically stable structure that
is not specifically disallowed by the laws of physics can in fact be built. The
possibility of building things atom by atom was first introduced by Richard Feynman
"assembler", which is little more than a submicroscopic robotic arm
can be built and be controlled. We can use it to secure and position compounds
in order to direct the precise location at which chemical reactions occur. This
general approach allows the construction of large, atomically precise objects
by initiating a sequence of controlled chemical reactions. In order for this to
function as we wish, each assembler requires a process for receiving and executing
the instruction set that will dictate its actions. In time, molecular machines
might even have onboard, high speed RAM and slower but more permanent storage.
They would have communications capability and power supply.
is expected to touch almost every aspect of our lives, right down to the water
we drink and the air we breathe. Experimental work has already resulted in the
production of molecular tweezers, a carbon nanotube transistor, and logic gates.
Theoretical work is progressing as well. James M. Tour of Rice University is working
on the construction of a molecular computer. Researchers at Zyvex have proposed
an Exponential Assembly Process that might improve the creation of assemblers
and products, before they are even simulated in the lab. We have even seen researchers
create an artificial muscle using nanotubes, which may have medical applications
in the nearer term.
computer has the capacity to perform 1012 operations in one seconds but it has
220,000 hardware defects and still has performed some tasks 100 times faster than
single-processor .The defect-tolerant computer architecture and its implications
for moletronics is the latest in this technology. So the very fact that this machine
worked suggested that we ought to take some time and learn about it.
a 'defect-tolerant' architecture through moletronics could bridge the gap between
the current generation of microchips and the next generation of molecular-scale
The interaction between cells is Coulombic, and provides
the necessary computing power. No current flows between cells and no power or
information is delivered to individual internal cells. Local interconnections
between cells are provided by the physics of cell-cell interaction. The links
below describes the QCA cell and the process of building up useful computational
elements from it. The discussion is mostly qualitative and based on the intuitively
clear behavior of electrons in the cell.
Aspects of QCA
A QCA cell consists of 4 quantum dots positioned at the
vertices of a square and contains 2 extra electrons. The configuration of these
electrons is used to encode binary information. The 2 electrons sitting on diagonal
sites of the square from left to right and right to left are used to represent
the binary "1" and "0" states respectively. For an isolated
cell these 2 states will have the same energy. However for an array of cells,
the state of each cell is determined by its interaction with neighboring cells
through the Coulomb interaction.
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