On 12/30/2013 3:09 AM, Bruno Marchal wrote:

But that's essentially everything, since everything is (presumably) quantum. Butnotice the limitation of quantum computers, if it has N qubits it takes 2^N complexnumbers to specify its state, BUT you can only retrieve N bits of information from it(c.f. Holevo's theorem). So it doesn't really act like 2^N parallel computers.## Advertising

OK, but nobody pretended the contrary. You can still extract N bits depending on the2^N results, by doing some Fourier transfrom on all results obtained in "paralleluniverses". This means that the 2^N computations have to occur in *some* sense.

`But they pretend that the number 2^N is so large that it cannot exist in whole universe,`

`much less in that little quantum computer and therefore there must be other worlds which`

`contain these enormous number of bits. What Holevo's theorem shows is the one can regard`

`all those interference terms as mere calculation fictions in going from N bit inputs to N`

`bit outputs. It is conceptually no different than doing a calculation in ordinary`

`probability theory: I start with some initial conditions and I introduce a probability`

`distribution and compute a probability for some event. In that intermediate step I`

`introduced a continuous probability distribution which implies an *infinite* number of`

`bits. Nobody thinks this requires an infinite number of worlds.`

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