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Fig. 15.11. An illustration of a carbon
nanotube transistor. IBM has built chips
with more than ten thousand nanotube
transistors.
Fig. 15.12. New electronic components called memristors have the potential to transform the market for solid-
state memory devices. A memristor has resistance to electrical current, but the resistance changes as the
current changes. When the current is removed, the memristor preserves the memory of its last resistance. In
this image, each of the white spots is a memristor only fifty nanometers in diameter.
Quantum computing
The study of the limits imposed by quantum mechanics on computers prob-
ably became respectable as an academic field after physicist Richard Feynman
gave a keynote talk at a conference on the “Physics of Computation” at MIT in
1981. In his speech, Feynman talked about the problem of performing a com-
puter simulation of physics:
I'm not happy with all the analyses that go with just the classical theory,
because Nature isn't classical, dammit, and if you want to make a simulation
of Nature, you'd better make it quantum mechanical, and by golly it's a
wonderful problem, because it doesn't look so easy. 13
Feynman proposed building a computer out of elements that obey quantum
mechanical laws:
Can you do it [simulate quantum mechanics] with a new kind of computer - a
quantum computer? … It's not a Turing machine, but a machine of a different
kind. 14
B.15.8. Stan Williams received a
doctorate in physical chemistry
from Berkeley. He is director of the
Memristor Research Group at HP
Labs in Palo Alto. In 2000, Williams
was awarded the Feynman Prize in
Nanotechnology.
As we have seen, the basic principles of a Turing machine - that simple, theo-
retical computational device devised by Alan Turing in 1936 - underlie the oper-
ation of all conventional computers. Yet, as Feynman pointed out, a computer
operating according to the laws of quantum mechanics would be a new kind
 
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