Quantum Computing

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Quantum Computing

• David Dvorak
• CIS 492

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Quantum Computing Overview

• What is it?
• How does it work?
• The basics
• Clarifying with examples
• Factoring
• Quantum Cryptography
• Why should we care?
• Societal implications
• Bugs to work out
• How will it affect the future?
• References

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One analogy
A quantum computer is to a regular computer,
what a laser is to a lightbulb. --Seth Lloyd,
MIT
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What is Quantum Computing?

• Currently, computer chips are filled with gates
  only fractions of a micron wide
• Gates will move to the atomic level
• At an atomic level matter obeys different rules
• Quantum Mechanics
• Allows completely new algorithms
• Better than cramming more gates on a chip
• Theoretical beginnings in the 80s, experiments in
  the 90s

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The Basics of Quantum Computing

• An atom, not an electron, is the physical bit
• An electron is 0 or 1
• Quantum mechanics at atom is 0, 1, or both
• coherent superposition
• The bit in quantum mechanics is a qubit
• Whats the difference?
• n bits can store one of 2n numbers at any time
• n qubits can store all 2n numbers at once

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The advantage of qubits

• Adding qubits increases storage exponentially
• Can do operations on all superpositionslike
  parallel computation
• One math operation on 2n numbers encoded with n
  bits requires 2n steps or 2n parallel processors
• The same operation on 2n numbers encoded by n
  qubits takes 1 step
• This makes complex problems much easier

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Example Factoring

• Factoring takes longer as digits increase
• Increasing CPU speed only increases calculation
  linearly, need exponentially
• Factoring 1000 digit number classically would
  take longer than estimated life of universe
• Quantum computers do this in minutes

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Other uses of Quantum Computing

• Modeling large complex systems
• the brain
• the universe
• Can describe an atom with a few bits
• Takes 100 bits to describe atoms interacting
• 2100 or 10100 bits, 1090 particles in whole
  universe
• Few 100 qubits easily solves this problem
• physics or chemistry

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Cryptography

• RSA cryptography relies on the difficulty of
  factoring large numbers to be secure

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Quantum Cryptography

• To break RSA a hacker would need a large scale
  quantum computer (10,000 qubits)
• Quantum computing offers new possibilities for
  secure communication
• entanglement
• two quantum bits correlated stronger than
  possible in regular physics
• teleportation
• two entangled objects can only be known by their
  ownersprivacy implications

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Quantum Cryptography

• Entangled atoms are like keys
• Cannot be known to anyone else by laws of quantum
  physics
• Has transmitted securely over 1km
• Bank of England wants to use it locally
• However, transmissions easily interrupted
• Denial of service
• However, eavesdroppers are easily detected
• Can intercept and retransmit, but it will be know

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Societal implications

• Has increased thinking, quantum computing opens a
  world of possibilities
• Common language between the sciences math,
  physics, chemistry, computers
• Thinking of complex problems to solve
• Secure communication
• Biggest advance yetchanges the way we think of
  the universe, ie, Schroedingers cat

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Kinks to work out

• Must reduce decoherence
• Computation spreads beyond local components,
  effects other qubits
• Qubits must only interact with themselves, not
  their environment
• Must control quantum phenomenon
• Make quantum computers scalable
• Current quantum computers have 10 or so qubits
• 1000s of qubits would be ideal

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The future of quantum computing

• In 100 years quantum computers will be boring
• Maybe not in all households, but common
• Molecular computers in households?
• Developing better cryptography
• Think up more problems to solvewont be able to
  solve them quite yet

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References

• www.qubit.org (Barneco and Ekert)
• www.qubit.org/library/intros/comp/comp.html
• www.qubit.org/library/intros/crypt.html
• www.pbs.org (Lloyd, Divincenzo, and Whaley)
• www.pbs.org/kcet/closertotruth/transcripts/308_qua
  ntumcomputers.pdf
• www.pbs.org/kcet/closertotruth/explore/learn_08.ht
  ml

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The End

• Questions?