On Saturday, September 21, 2019 at 7:29:08 AM UTC-5, Alan Grayson wrote:
>
>
>
> On Saturday, September 21, 2019 at 6:23:18 AM UTC-6, John Clark wrote:
>>
>> There is a rumor that a team of researchers at Google led by John
>> Martinis have performed a calculation on a Quantum Computer in three
>> minutes and 20 seconds that would have taken Summit, the most powerful
>> conventional supercomputer in the world, 10,000 years to perform. The rumor
>> started when a paper stating that was posted by the Google team, apparently
>> accidentally, on a NASA website and then quickly taken down. It's not clear
>> exactly what the calculation was about, they just said it “marks the first
>> computation that can only be performed on a quantum processor". My guess is
>> it was probably a weird function of some sort that would not be of much use
>> to a scientist or engineer, but even so if true it would be a first
>> proof of concept and be earthsharing. I suppose they want to check and
>> recheck their work before they make a official announcement this important
>> and that's why they took the article down.
>>
>
> What I don't understand is why a computer programmed to assume a
> superposition, say of two states, represents a system in both states
> simultaneously (which I find to be false for reasons previously stated),
> would speed up any calculation. Can anyone answer this question? AG
>
>>
>>
>> John K Clark
>>
>
Since quantum computers are in a superposition of various states a search
down a branching tree, say a search along a maze, can be done in a
superposition of states. This would appear to argue that a quantum computer
can do an NP, nondeterministic polynomial or non-polynomial, problem in P
time and space. Not quite, for in order to read the outcome there must be
classical signals transmitted on state preparations and so forth. This
means quantum computers are polynomial, but considered to be "bounded
quantum polynomial." This means they are a considerable speed up, but not
exponentially so.
What has me a little mystified is now they computed something for 3 minutes
and 20 seconds. It would be an astounding breakthrough if the quantum
computer ran continuously for that time. Decoherence will usually demolish
a qubit within 10^{-5}sec, unless this employs some sort of quantum error
correction code of a novel form. I suspect it ran the algorithms in time
steps, where it ran for 10^{-6}sec, transferred to classical data that was
used to prepare quantum states for the next quantum iteration and so forth.
LC
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