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#1 DK3250   User is offline

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Do anyone explain Quantum Computing - at intermediate level?

Posted 04 November 2019 - 06:02 AM

There is currently much hype about Quantum Computing.
But what is it really?

I think I do understand superposition, but I cannot bridge the gap from simple Quantum systems to computing.
Can anyone explain how a quantum computer works?
Or point to a book or an article explaining this?

The explanation needs to go beyond the Wikipedia explanation and provide a firm understanding of not only the basic quantum principles but also how this is utilized in practical computing. On the other hand it should be simple enough to avoid the excessive math provided in the link by macosxnerd101.

Thank you in advance.

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#2 modi123_1   User is offline

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Re: Do anyone explain Quantum Computing - at intermediate level?

Posted 04 November 2019 - 08:45 AM

Oddly, Microsoft has a good swath of information on this topic including an 'QDK'. It may help you narrow in on a more technical level.

https://www.microsof.../en-us/quantum/
https://www.microsof...development-kit
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#3 jon.kiparsky   User is online

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Re: Do anyone explain Quantum Computing - at intermediate level?

Posted 04 November 2019 - 08:49 AM

Maybe start here? https://www.smbc-com...omic/the-talk-3
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#4 macosxnerd101   User is offline

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Re: Do anyone explain Quantum Computing - at intermediate level?

Posted 04 November 2019 - 08:58 AM

Quote

but also how this is utilized in practical computing


Quantum computing is not practical. Any quantum computer that exists is in a lab, and it is definitely not factoring integers.

There are several areas in quantum computing, including quantum algorithms, quantum cryptography, quantum coding theory, and quantum information. Out of all of these, quantum algorithms is an area that is considered a dead end. We really aren't any further along than we were in the 90s with the development of Shor's algorithm and Grover's algorithm. Any algorithms developed since then are minor variations of these two.

Practically, this means that you shouldn't expect to develop your own (useful) quantum algorithm.


Quote

On the other hand it should be simple enough to avoid the excessive math provided in the link by macosxnerd101.


The key idea in quantum computing is as follows. Consider a three-dimensional sphere of radius one. Quantum states are points on this sphere. A quantum algorithm works by preparing an initial state, rotating the sphere, doing work, then rotating back. We then read off the new state and draw conclusions about it. This is the primary trick in quantum computing. Quantum random walks are also a thing, but I am unsure of how successful they have been in yielding new algorithms. Using classical random walks to design classical algorithms is a standard technique, so generalizing it to the quantum setting is a natural approach.

The math behind this is a lot of algebraic geometry. We can get away by phrasing it in the language of linear algebra and complex variables. That said, the linear algebra can be a barrier for those not in math or theory. The one class on Quantum Computing that I took spent about a month developing the linear algebra and complex variables so that we could talk about quantum computing. It was a month before we defined a qubit (as a two-dimensional Hilbert space). I don't think Quantum Computing is an approachable subject, personally. There is a lot of background material.


On the other hand, if you are interested in general information on the recent buzz around Google's quantum computing breakthrough, Scott Aaronson has an FAQ (https://www.scottaaronson.com/blog/?p=4372). He is one of the top people in this field.

This post has been edited by macosxnerd101: 04 November 2019 - 09:00 AM

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#5 DK3250   User is offline

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Re: Do anyone explain Quantum Computing - at intermediate level?

Posted 04 November 2019 - 02:48 PM

modi123_1, jon.kiparsky and macosxnerd101:
You are all my heroes.
Thank you for great links, great insight and your great spirit. :bananaman:/>

I've up-voted you all, - wish I could double it.
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#6 jon.kiparsky   User is online

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Re: Do anyone explain Quantum Computing - at intermediate level?

Posted 05 November 2019 - 01:51 PM

I came across an interesting SO thread about this
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