On 8/7/2019 2:56 PM, Philip Thrift wrote:
On Wednesday, August 7, 2019 at 2:59:04 PM UTC-5, Brent wrote:
On 8/7/2019 11:15 AM, Philip Thrift wrote:
On Wednesday, August 7, 2019 at 1:03:44 PM UTC-5, Brent wrote:
On 8/7/2019 1:08 AM, Philip Thrift wrote:
On Tuesday, August 6, 2019 at 5:29:04 PM UTC-5, Brent wrote:
On 8/6/2019 11:25 AM, Philip Thrift wrote:
On Tuesday, August 6, 2019 at 1:00:23 PM UTC-5, Brent
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.
Yet this is the kind of algorithm that Deutsch
cites as proving there must be many worlds.
Brent
That there is a multiplicity of /somethings/
https://en.wikipedia.org/wiki/Multiple_histories
<https://en.wikipedia.org/wiki/Multiple_histories>
is the basis for all semantics of quantum computing (by
computer scientists) that I have ever seen.
Same for classical computation...there are lots of
states or functions. Did anyone think there had to be
multiple worlds for the computer to work?
Brent
There is classical parallel hardware, e.g. made with
multiple processors.
Parallelism in quantum computers is achieved by parallel
"worlds" or "paths":
Quantum Path Computing
- https://arxiv.org/abs/1709.00735
<https://www.google.com/url?q=https%3A%2F%2Farxiv.org%2Fabs%2F1709.00735&sa=D&sntz=1&usg=AFQjCNFru47zPN3LturOmKgNuixbWCjlHg>
Quantum circuit dynamics via path integrals: Is there a
classical action for discrete-time paths?
-
https://iopscience.iop.org/article/10.1088/1367-2630/aa61ba
<https://iopscience.iop.org/article/10.1088/1367-2630/aa61ba>
But as you note with scare quotes, calling those "worlds" or
"paths" is just metaphorical. They are not worlds you can
visit or paths you can take. They are aspects of mathematical
abstractions.
Brent
A “problem of time” in the multiplicative scheme for the
n-site hopper
Fay Dowker, Vojtˇech Havlicek, Cyprian Lewandowski, and
Henry Wilkes
-
https://pdfs.semanticscholar.org/39d9/11e25b835ce8d34910c0a9e02f22ef8d4c41.pdf
<https://pdfs.semanticscholar.org/39d9/11e25b835ce8d34910c0a9e02f22ef8d4c41.pdf>
"Quantum Measure Theory (QMT*) is an approach to quantum
mechanics,
based on the path integral, in which quantum theory is
conceived of as a generalized stochastic process."
*
https://pdfs.semanticscholar.org/bfda/1caa5afbbd9e2d6dcff5456325b60b64b909.pdf
<https://pdfs.semanticscholar.org/bfda/1caa5afbbd9e2d6dcff5456325b60b64b909.pdf>
The sum-over-histories formulation of quantum computing
- https://arxiv.org/abs/quant-ph/0607151
<https://arxiv.org/abs/quant-ph/0607151>
@philipthrift
If a multiplicity of somethings isn't present in a quantum
computer, then how does the speedup occur?
By not decohering at every bit flip and keeping the single state
rotating.
Brent
Then how does an answer come out?
By decoherence at the end.
Like in the solution here: https://arxiv.org/abs/1709.00735
QPC solves specific instances of simultaneous Diophantine
approximation problem (NP-hard) as an important application.
QPC does not explicitly require exponential complexity of resources by
combining tensor product space of path histories inherently existing
in the physical set-up and path integrals naturally including histories.
Interesting, but looks more aspirational than proven. It reminds me of
attempts to solve NP-hard problems using some analog schemes.
Brent
more here: https://faculty.ozyegin.edu.tr/burhangulbahar/publications/
@philipthrift
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