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"Quantum freeze" rescues world’s fastest computers

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21.08.2003

Whilst western Europe is feeling the effects of global warming, a “freeze” has come to the rescue of quantum computing.

Quantum Computers – computers so fast they could break any code devised for a digital computer – have a fatal flaw which has until now made it impossible to build really fast quantum computers. They make so many operations that very rare and tiny errors occur rapidly and are amplified, making them unable to function properly.

The Institute of Physics and German Physical Society journal New Journal of Physics today publishes a paper which describes a phenomenon which could eliminate the majority of these errors and allow these computers to operate at incredible speeds successfully.

Tomaz Prosen and Marko Znidaric, researchers from the University of Ljubljana in Slovenia, have successfully produced what they call a “quantum freeze of fidelity” which under certain conditions eliminates a whole set of errors. Their idea describes the stability of quantum dynamics in a general class of mathematical models. It is believed that the application of this idea in quantum computation will allow scientists to target the most dangerous errors and eliminate them, making super-fast quantum computers possible.

Dr. Prosen said: “The mechanism of the quantum freeze of fidelity, which drastically enhances the stability of quantum computation, is simple and yet has no analogue in classical physics. It is a kind of quantum demon at work. We hope it can be employed in a practical quantum computation.”

At present, quantum computers of about four qubits have been built. A qubit (or quantum bit) represents an arbitrary superposition of zero and one at the same time, e.g. 30% zero and 70% one. Two qubits represent an amplitude (or probability) for every possible two-bit number (e.g. 00, 01, 10, 11). Each additional qubit increases the number of possible numbers exponentially. So, twenty qubits represent every number from 0 to more than one million, 30 qubits represent every number from 0 to more than one billion, and 40 qubits represent every number from 0 to more than one trillion. A quantum computer acts on a set of particles by influencing the probabilities of the particles’’ spins (posing the problem) so that when the particles leave their quantum state the resulting spins represent a specific number (getting the answer).

Quantum computers have the potential to be a thousand times faster than today’s computers because they operate on all the particles - and thus all the possible numbers - simultaneously.

David Reid | Source: alphagalileo
Further information: stacks.iop.org/1367-2630/5/109

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