On 8/7/2019 2:31 AM, Bruno Marchal wrote:
On 7 Aug 2019, at 00:37, Bruce Kellett <[email protected]
<mailto:[email protected]>> wrote:
On Wed, Aug 7, 2019 at 4:00 AM 'Brent Meeker' via Everything List
<[email protected]
<mailto:[email protected]>> wrote:
On 8/6/2019 6:38 AM, Bruno Marchal wrote:
If the QC does its task effectively, the output basis qbits
will be put into definite states,
Relatively to the observer, but in the global state, the
observer will inherit the superposition state, by linearity of
the tensor products and of the evolution.
In something like Shor's algorithm there is only one final state
with non-vanishing probability.
Exactly. So there are no other components in superposition. Bruno
wants to characterize this as a collapse. But without this
happening, the QC would be unreliable -- there would be some finite
probability that you would get the wrong result. As I understand it,
there are some QC algorithms that do not lead to definite results, so
you have to run them several times to reduce the probability of a
wrong answer to some acceptable level.
As usual, Bruno is introducing irrelevancies in order to distract
attention from the fact that he cannot answer the central contention
of my argument -- which is that quantum computer do not provide any
evidence for the existence of parallel worlds. They can work
perfectly well in just one world -- without any collapse whatsoever.
I can’t explain even just the two slits without superposition.
“Parallel worlds/histories” are just a popular name to describe a
superposition. Then nothing in the QM linear evolution can explain how
the superposition disappear, although the decoherence theory explain
why it is hard to see a macro-superposition.
Shor algorithm does not make them disappear, even if it manages to get
the result with high probability in the branch we are situated in.
It gets the result with the same high probability (/and by the same
means/) that a classical computer, or a mathematician with pencil and
paper get the answer.
Brent
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