Quantum Computing: A view from the enemy camp

SIGFPE writes "There seems to be an unthinking acceptance by many people that quantum computers are now on their unstoppable way up and before too long we'll be cracking RSA and simulating protein folding on complex quantum computers. However there is another point of view that considers quantum computers to be as difficult to make as perpetual motion machines - and for much the same reason: entropy. As an antidote to all the successes that have been reported on /. here is a just published and highly readable preprint by a sceptical mathematical physicist."

Comments

Re:parallel processing

[jvv62]

"If it is possible to utilize parallel processing then life would have had to evolve the ability to take advantage of that." - Perdo

Ummm....

While this sentence is taken out of context, it is still completely wrong. We use parallel processing all the time. The parallel computation part of quantum computing seems to work in both theory and in the lab as well.

Assume that there exists an efficient (classical) algorithm for calculating f(x) for a given x, however if n is large, say 1000, calculation for all x would take quite a lot of time. The quantum computer, in a certain sense, performs all these calculations much faster, during a time which is not exponential, but polynomial in n. (I note in passing, that the difficulty of building a quantum computer increases exponentially with n, which is a kind of Nature's revenge). -Dyakonov

The argument against QC is really much simpler than Perdo's convoluted logic requires. Dyakonov says that the problem isn't that a quantum computer couldn't do the calculations fast. The problem is that it would take nearly forever to build the computer in the first place.

Re:Achieveable accuracy

[superflex]

you're absolutely right about how atoms are in fact perpetual motion "machines". the whole idea of a "PMM" is a misnomer, because the idea behind it is not one of perpetual motion, but of perpetual work/energy. that's the part that isn't kosher, because it violates the first law of thermodynamics "energy cannot be created or destroyed".