[anoncoder]

See http://arxiv.org/abs/1401.4356, a paper by Ross Anderson and Robert Brady. They've since expanded the theory greatly, with other papers on arxiv.

Also, check out this fascinating debate about these matters on Scott Aaronson's blog. Link is http://www.scottaaronson.com/blog/?p=1255

Brady and Anderson have many posts in this debate, and IMHO, wind up winning.

It's looking more and more like physics took a wrong turn with the Copenhagen interpretation of quantum mechanics.

[jeffsco]

I am biased as a Scott A. fan and as somebody who knows essentially nothing about QM. However I see no way to conclude that Anderson and Brady even know what they're talking about, much less that they win the debate on the linked Scott Aaronson page. I just read through it again to confirm my recollection (skipping the Motl and Sidles posts fwiw).

[anoncoder]

The main reason I felt Scott A. (and company) lost the debate is because he could not point to a single experiment that actually uses qubits to do a calculation above a very small threshold. There is much written about experiments that seem to show entanglement of multi qubit systems, but none of them actually do any calculations with the qubits.

Brady and Anderson's point is that it's not a qubit until you can calculate with it. And their theory suggests it will get exponentially harder for each qubit above 4 (I think), which throws out all of the interesting quantum algorithms.

I also felt Brady and Anderson silenced every objection. After one or more of their rebuttals, they were no longer challenged. The most recent post about Feynman is also interesting.

In any event, it is a fascinating blog post.