an outgrowth of older p/n junctions and newer research
in nano and quantum scale effects. Processors and
devices that rely on p/n junctions (nearly all modern
electronics) are based on quantum effects - including
the mighty transistor, the building block for all computers.
What's being discovered is it may be possible to
engineer 'virtual atoms', and these in turn may prove
to have as many uses as the transistor.
See these pages for a good overview of quantum dots,
with a few animations:
http://www.evidenttech.com/qdot-definit ... uction.php
Tiny groups or balls of atoms, usually less than 10-20
nanometers in diameter, are small enough to demonstrate
quantum effects (not the 'bulk' effects that large
groups of atoms display). At this scale the wave-like
nature of matter dominates, and the entire group of
atoms beahaves like a single entity. This can make
it hard to predict ahead of time how these things will
behave. The atoms in a quantum dot can not be considered
separate from one another. On the quantum scale they
are all 'entangled' to a certain degree and only
by considering the dot as a single quantum mechanical
system can its behavior be predicted.
Another problem is actually constructing these tiny
devices. Most modern processors use a process known
as lithography to create the tiny circuits on the
die. This technique currently is just knocking
on the door of the quantum realm - the smallest feature
size is currently around 40-100 nanometers. So to create
quantum dots entirely new fabrication techniques are
being developed using chemical and 'self-assembly'
techniques.
As a related example, see this page for an animation
of the construction of a blue diode laser, which
are going to be used in the next generation of
digital recording devices. You can see the exquisite
control that's needed to construct these tiny
devices.
http://mrsec.wisc.edu/Edetc/LED/LEDprep.htm
Using a process known as 'metal oxide chemical vapor
deposition' (MOCVD) thin layers of materials are
stacked on top of each other. Note the quantum well
where the lasing action occurs is only 50 nanometers
thick.
See also this interview with Shuji Nakamura, the creator
of the first blue/violet diode lasers (and LEDs):
http://www.sciencewatch.com/jan-feb2000 ... _page4.htm
Practical uses for quantum dots are just starting to
appear.
{energy technology}
Nanosolar claims to be perfecting a printing press technique
to manufactor PV arrays at a fraction of the cost of conventional
silicon solar cells, with similar efficiencies (10-15 %)
This technique relies on quantum dots
http://www.nanosolar.com/ThirdWaveSolarPower.htm
In addition, it may now be possible to use quantum dots
to increase the fundamental efficiency of PV cells by
releasing more than one electron per photon absorbed
by the material (as has already been discussed).
Probably the most speculative and exciting uses for
quantum dots are in the field of computer science.
nano and molecular sized transistors may represent
the ultimate in size and switch times, being orders
of magnitude faster than current transistors. There's
even talk of using quantum superposition interference
effects to do many computations in parallel and quantum
dots could be used as computer memory. In theory, again using
superposition, it may possible to create a memory with
2^1000 bits (enormous beyond reckoning) using one
atom per bit (1000 atoms).
Some theorists (david deutsch) have asserted that
quantum computing proves the 'multiverse' interpretation
of quantum mechanics. This mind blowing theory posits
every time a 'condition' occurs the universe 'splits'
and we actually inhabit a seething 'multiverse' He
uses this to explain the classic two-slit diffraction
experiment, as well a certain forms of quantum computing
(his book _the fabric of reality_ is worth a read, though
I do think he goes off the deep end at times).
from:
http://en.wikipedia.org/wiki/David_Deutsch
$this->bbcode_second_pass_quote('', '
')Deutsch: "To those who still cling to a single-universe world-view,
I issue this challenge: explain how Shor's algorithm works." The challenge
is meant to imply that a Turing machine is incapable in principle of
doing what a quantum computer can do, since the latter's operations in
executing Shor's algorithm require computational resources from other
worlds. And generally, a quantum computer's operations include computational
steps in other worlds that are not present in any Turing-machine's tape
(in this world). Deutsch thinks this has implications for proof theory,
which must abandon the model of an inspectable list of premises leading
to a conclusion, in favor of a model of a process in which the relationship
between premises and conclusion may be mediated by computations that are not
inspectable (in this world).
