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Quantum Computing

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  1. Quantum Computing David Dvorak CIS 492

  2. 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

  3. One analogy… “A quantum computer is to a regular computer, what a laser is to a lightbulb.” --Seth Lloyd, MIT

  4. 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

  5. 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 • What’s the difference? • n bits can store one of 2n numbers at any time • n qubits can store all 2n numbers at once

  6. The advantage of qubits • Adding qubits increases storage exponentially • Can do operations on all superpositions…like 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

  7. 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

  8. 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

  9. Cryptography RSA cryptography relies on the difficulty of factoring large numbers to be secure…

  10. 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 “owners”…privacy implications

  11. 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

  12. 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 yet…changes the way we think of the universe, ie, Schroedinger’s cat

  13. 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

  14. 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 solve…won’t be able to solve them quite yet

  15. 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_quantumcomputers.pdf • www.pbs.org/kcet/closertotruth/explore/learn_08.html

  16. The End Questions?

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