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- Brief History
- Explanation of Concept
- Understanding the Concept
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- First explored in the 1970's and early 1980's
- Scientists were pondering the fundamental limits of computation
- Moore's Law
- The continually shrinking size of circuitry packed onto silicon chips
would eventually reach a point where individual elements would be no
larger than a few atoms
- Raised the question of whether a new kind of computer could be devis=
ed
based on the principles of quantum physics
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- Quantum technology can offer much more than cramming more and more b=
its
to silicon and multiplying the clock-speed of microprocessors.
- It can support entirely new kind of computation with new algorithms
based on quantum principles!
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- An algorithm is a precise set of instructions used by computers that=
can
be mechanically applied to yield the solution to any given instance =
of a
problem.
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- A light source emits a photon along a path towards a half-silvered
mirror. This mirror splits the light, reflecting half toward
detector 1 and transmitting half toward detector 2. A photon,
however, is a single quantized packet of light and cannot be split, =
so
it is detected with equal probability at either A or B. Intuit=
ion
would say that the photon randomly leaves the mirror in either
direction. However, quantum mechanics predicts that the photon actua=
lly
travels both paths simultaneously!
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- Here, the photon first encounters a half-silvered mirror, then a ful=
ly
silvered mirror, and finally another half-silvered mirror before
reaching a detector, where each half-silvered mirror introduces the
probability of the photon traveling down one path or the other.
Once a photon strikes the mirror along either of the two paths after=
the
first beam splitter, the arrangement is identical to that in figure =
a,
and so one might hypothesize that the photon will reach either detec=
tor
1 or detector 2 with equal probability. However, experiment sh=
ows
that in reality this arrangement causes detector A to register 100% =
of
the time, and never at detector B!
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- It seems inescapable that the photon must, in some sense, have actua=
lly
traveled both routes at once for if an absorbing screen is placed in=
the
way of either of the two routes, then it becomes equally probable th=
at
detector 1 or 2 is reached.
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- In other words, a classical computer would be able to do anything a
quantum computer can.
- So why bother with quantum computers?
- Although a classical computer can theoretically simulate a quantum
computer, it is incredibly inefficient, so much so that a classical
computer is effectively incapable of performing many tasks that a
quantum computer could perform with ease.
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- http://www.qubit.org/library/intros/comp/comp.html
- http://www.cs.caltech.edu/~westside/quantum-intro.html
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