An Introduction to Quantum Computation and （介绍量子计算和）.pdf
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An Introduction
to
Quantum Computation
and
Quantum Communication
Rob Pike
Bell Labs
Lucent Technologies
rob@
June 23, 2000
Introduction
1
An analogy:
Newtonian physics is an approximation to Einsteinian physics
(general relativity).
Classical physics is an approximation to quantum mechanics.
Classical information is an approximation to quantum
information.
In each case, the approximation excludes important details but
serves well for many purposes.
In each case, removing the approximation requires deeper
understanding and harder math, but results in a truer picture of
Nature and may enable new technologies.
Yes, Nature: we’re beginning to understand that information is
a physical concept.
What approximation do we remove?
2
Relativity: we remove (among others) the approximation that
we are traveling much slower than light.
Quantum mechanics: we remove (among others) the
approximation that we are manipulating things much larger
than atoms.
Quantum computation: we remove (among others) the
approximation that the elements of information are
independently manipulable.
Why would we care?
3
That approximation means that we can look at one bit in a
register without affecting the other bits.
Why remove that approximation? Because it limits the power
of the computer. (Keep in mind the analogies.)
Also, getting ahead of ourselves, that approximation turns out
to be troublesome in representing information quantum
mechanically.
Why would we do that?
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