
Shor's Quantum Factoring Algorithm (2017) - sjcsjc
https://algassert.com/post/1718
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shagie
Another explanation (that I’m fond of) is in Shor, I’ll do it :
[https://www.scottaaronson.com/blog/?p=208](https://www.scottaaronson.com/blog/?p=208)

> I’ve been talking a lot recently about how quantum algorithms don’t work.
> But last week JR Minkel, an editor at Scientific American, asked me to write
> a brief essay about how quantum algorithms do work, which he could then link
> to from SciAm‘s website.”OK!” I replied, momentarily forgetting about the
> 10^10^5000 quantum algorithm tutorials that are already on the web. So,
> here’s the task I’ve set for myself: to explain Shor’s algorithm without
> using a single ket sign, or for that matter any math beyond arithmetic.

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andreareina
Clicking through to the post about Grover's Algorithm[1] is the mental model
of all the quantum stuff that works best for me: "Like probability theory, but
over the complex numbers".

[1][http://twistedoakstudios.com/blog/Post2644_grovers-
quantum-s...](http://twistedoakstudios.com/blog/Post2644_grovers-quantum-
search-algorithm)

~~~
all2
> "Like probability theory, but over the complex numbers".

I'm a probability novice. How would this work? Are we talking vector fields
representing multidimensional probabilities? Or just probabilities that happen
to depend on more than one variable?

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kirrent
Just that if you have a quantum system, such as a qubit consisting of the |0>
state and |1> state with a combination over the two (called a superposition)
represented by a|0> \+ b|1> then a and b can be complex. This is in contrast
to classical mechanics where, for example, pr(heads) and pr(tails) must both
be real.

It's only once it comes to actually making a measurement that you need to get
real again.

~~~
Y_Y
Probabilities are also always real in quantum mechanics.

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osamagirl69
Really a well written summary! A good, but not overwhelming, about of depth.

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gregoronio
Damn, this must be old. It has a Code Monkey reference. That's some dusty
lore.

