Quantum Computers

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Quantum Computers

• As if computers werent fast enough already

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Brief Outline

• Introduction What is a quantum computer?
• Differences from classical computers
• Power(speed,efficiency, etc.)
• History
• Problems
• Conclusion

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What is a quantum computer?

• Computer using the laws of quantum mechanics
• Utilizes physical phenomena
• Quantum interference
• Superposition
• May seem to defy logic
• Mostly theoretical many of the ideas cannot
  work due to quantum nature

Photon Split?
No!
-gt
Classical Idea
Quantum Idea
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The difference between classical and quantum
computers

• Classical
• Bits storage in 0s and 1s
• Uses Boolean logic gates to manipulate bits
• Macroscopic physical storage
• Charge, magnetization, etc.
• Governed by the same laws as everyday phenomena
• Can only manipulate one piece of data at a time
• Quantum
• Qubits storage in 0s, 1s, or a superposition
  of both.
• Executes quantum gates to act as unitary
  transformations on qubits
• Uses quantum laws which differ greatly from
  everyday phenomena
• Can manipulate many pieces of data at once

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Computing speed and efficiency

• Qubit can hold as many values at once as a bit
  has range to hold
• 3 bits can hold one number up to 8
• 3 qubits can hold 8 numbers up to 8
• Can perform many computations at the same time,
  as opposed to performing them one at a time
• Factoring, as an example
• Peter Shor, ATT Bell Laboratories, New Jersey

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History

• Idea developed from the idea of elements being
  small enough to behave on the quantum level
• 1982 Feynman comes up with idea for
  computations. Says quantum computers can be used
  for quantum simulations.
• 1985 Duetsch realized Feynmans assertion could
  lead to a general purpose computer and published
  a paper that showed how.
• 1994 Shor circulates a preprint of a paper
  showing how quantum computers could solve many
  mathematical problems many times faster than
  classical computers (namely factorization).
• 1995 Theory of quantum error correction
• 1998 Researchers at Los Alamos National
  Laboratory and MIT led by Raymond Laflamme spread
  a qubit across three nuclear spins in each
  molecule of a liquid solution of alanine or
  trichloroethylene molecules possible with NMR
  (nuclear magnetic resonance)
• Spread makes it harder to corrupt can
  indirectly measure decoherence and compare spin
  states
• Present - http//www.cs.berkeley.edu/vandam/homes
  .html

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Problems

• Decoherence tendancy of quantum computer to
  decay as it interacts (entangles) with the
  outside environment
• Qubits cannot be directly measured lose
  superposition and change to 0 or 1 when attempted
• May try to set up an algorithm to cycle through
  qubits after they are manipulated, narrowing down
  the possible answers, until the probability of
  the right answer showing up is close to 100
• Phase coherence may be used for error correction
• Architecture is too complicated, large, or
  expensive
• World is too dependent on current computer
  systems
• Ideas are fundamentally more difficult than
  classical computers

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Conclusion

• Quantum computer research is making breakthroughs
• We may someday have quantum computers for generic
  use
• Quantum computers could provide faster or better
  methods of doing most anything (encryption, as an
  example)
• There are too many problems for such
  breakthroughs to occur in the near future
• For those of you who have taken Quantum A B
  Quantum physics IS practical for something in our
  everyday lives your nights and weekends spent
  on homework were not spent in vain!

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References

• http//library.thinkquest.org/C008537/quantum/comp
  uters/computers.html
• http//www.cs.caltech.edu/westside/quantum-intro.
  html