The strange world of quantum computing

[zengrifter]

A detour into the strange world
of quantum computing

2/12/2007 12:16:26 PM, by John Timmer
Copyright © 1998-2006 Ars Technica

On Tuesday, a startup company called D-Wave is going to publicly demonstrate a quantum computing system that they call Orion. Is this the dawn of a new era of computing or simply an exercise in hype? It's hard to say prior to the announcement, but my guess is a little of both. To fully appreciate why, we'll have to take a detour into the strange world of quantum computing.

Speeding calculations through superposition

In what passes for normal in the quantum world, a properly prepared quantum object kept in isolation from the environment will actually exist in all possible states (be they energy, spin, etc.) at once—it exists as a superposition of states. Depending on the inputs to the system, a single state will be the most probable one occupied; repeated measurements of the same, freshly-prepared system can identify this most probable state. If you think of that object as a bit, it's easy to see how calculations can be done: set it in a ground state, perform a calculation by providing an input that influences its state, and then read it. Repeat the process a few times to get the probabilities sorted, and you've done a 1-bit calculation with a quantum bit, or qubit.

Needless to say, such a computer would badly underperform whatever is currently running your cell phone. But in the quantum world, two objects can be entangled; the state of one is linked to the state of another. Thanks to the combination of superposition and entanglement, this two-particle system will simultaneously exist in 22 states, but with only one probable state, influenced by experimental inputs. As more entangled particles are added, the system can simultaneously explore 2n possible answers, where n is the number of qubits.

...more - http://arstechnica.com/news.ars/post/20070212-8818.html