Monday, July 18, 2005

The Quantum Computer Condition

This looks like just what I want to read.

I'm a sceptic when it comes to quantum computers. Given a real quantum system, I expect it to diverge from an idealised mathematical description of it exponentially fast. The rate of divergence comes from the difference between the real and idealised Hamiltonians. This is generally pretty damn fast. There are lots of error correction schemes out there but they always assume the Hamiltonian has a special ideal form . Real Hamiltonians don't look like this so I expect the error correction merely to retard the exponential divergence. So I have grave doubts about whether quantum computers can do the kinds of things that many people would like them to do. I've a feeling quantum computers will eventally find a use, but it won't be anything like current researchers are doing. I don't see a rosy future for binary qubit machines outside of implementing (and not breaking) cryptography.

The above paper looks interesting as it apparently gives precise conditions for a quantum computer to function effectively in the presence of decoherence. That will help me to sharpen up (or even demolish) my arguments.

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