Quantum Computing David Dvorak CIS 492 Quantum Computing

Quantum Computing David Dvorak CIS 492

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

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

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 80 s, experiments in the 90 s

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 2 n numbers at any time – n qubits can store all 2 n numbers at once

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

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

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

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

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

Quantum Cryptography • Entangled atoms are like keys • Cannot be known to anyone else by laws of quantum physics – Has transmitted securely over 1 km – 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

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

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 – 1000 s of qubits would be ideal

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

References • www. qubit. org (Barneco and Ekert) – www. qubit. org/library/intros/comp. html – www. qubit. org/library/intros/crypt. html • www. pbs. org (Lloyd, Divincenzo, and Whaley) – www. pbs. org/kcet/closertotruth/transcripts/308_quantu mcomputers. pdf – www. pbs. org/kcet/closertotruth/explore/learn_08. html

The End Questions?