
An Interactive Introduction to Quantum Computing - kevlened
http://davidbkemp.github.io/QuantumComputingArticle/
======
robertkrahn01
Interesting in this regard might also be the talk that Robert Smith of Rigetti
Computing recently gave:
[https://www.youtube.com/watch?v=f9vRcSAneiw](https://www.youtube.com/watch?v=f9vRcSAneiw)

Apart from praising Common Lisp he describes how they are building an
assembler-like language for quantum computing.

The HN thread:
[https://news.ycombinator.com/item?id=15880172](https://news.ycombinator.com/item?id=15880172)

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westurner
Part 2 mentions two quantum algorithms that could be used to break Bitcoin
(and SSH and SSL/TLS; and most modern cryptographic security systems): Shor's
algorithm for factorization and Grover's search algorithm.

Part 2:
[http://davidbkemp.github.io/QuantumComputingArticle/part2.ht...](http://davidbkemp.github.io/QuantumComputingArticle/part2.html)

Shor's algorithm:
[https://en.wikipedia.org/wiki/Shor%27s_algorithm](https://en.wikipedia.org/wiki/Shor%27s_algorithm)

Grover's algorithm:
[https://en.wikipedia.org/wiki/Grover%27s_algorithm](https://en.wikipedia.org/wiki/Grover%27s_algorithm)

I don't know what heading I'd suggest for something about how concentration of
quantum capabilities will create dangerous asymmetry. (That is why we need
post-quantum ("quantum resistant") hash, signature, and encryption algorithms
in the near future.)

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oneweekwonder
> Sorry, I but cannot assume you know nothing at all!

Make the witty text a hyperlink to
[https://en.wikipedia.org/wiki/Boolean_algebra](https://en.wikipedia.org/wiki/Boolean_algebra)
?

~~~
pcjedi
<irony>Great Suggestion! Let no humor remain in scientific
explanations!<\irony> Seriously.. don't you get the joke?

~~~
oneweekwonder
> Seriously.. don't you get the joke?

Unfortunately it was lost on me then. It was a blue question [?] next to a
assumption the author has of the reader.

I hoped the [?] marked gave some insight or info into the assumption,

But rather you got a witty response, hence my suggestion, to keep the witty
response but also help people not in the know.

~~~
pcjedi
So I guess an explanation has to be very careful with that then. I liked the
style. Good way to make clear that this isn't some uptight explanation, but
the attempt to experience a little with the explanation style. But it comes
with the risk to just confuse people.

~~~
oneweekwonder
> I liked the style

Same here, still consuming it, gonna take a couple of days.

But then I'm sharing it with bossman and my mother.

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avodonosov
Long talk about superpositions of probabilities, but almost no explanation
about how can that help in _computing_.

How can the probabilistic operations speedup computations? No explanation
given.

~~~
jcoffland
It does show how 2-bit quantum search is faster than conventional, requiring
only one evaluation of the oracle function instead of three.

~~~
avodonosov
In the second part and not explaining the principle.

------
mozumder
I feel like theres potential here for quantum computers to represent
perceptrons in neural networks, since they seem to both operate with rough
states.

~~~
davidwihl
You mean
[https://en.m.wikipedia.org/wiki/Quantum_machine_learning](https://en.m.wikipedia.org/wiki/Quantum_machine_learning)

------
zimzim
why Hadamard of 1 is diffrent from Hadmard of 0?

~~~
cosenal
that's like asking why NOT of 1 is different from NOT of 0? If it was the
same, it would be the identity gate.

~~~
zimzim
I meant, physically, what gives different? why after applying the gate once on
1 there is a 50% the spins flip but when applying to 0 no-chance of that.

~~~
cosenal
The states you get are H(|0>)=|0>+|1> and H(|1>)=|0>-|1>, _both_ of which have
50% probablity to end up as 0 or 1 once they are measured. The difference of
the "-" in the second state is only visible if you carry on the computation,
not if you measure.

------
dvt
> Qubits represent 0 and 1 using quantum phenomenon like the nuclear spin
> direction of individual atoms.

Not trying to be _that guy_ but this is so wrong/misleading, it hurts (and I'm
not even a physicist!). Spin isn't a "direction" and atoms don't "spin" \--
well, they might, but the quantum kind of spin has nothing to do with angular
momentum.

~~~
zimablue
Not a physicist but I did study a degree in it. Spin is absolutely a direction
and absolutely related to angular momentum, since it's basically the angular
momentum that you get when all the angular momentum we understand is removed.

There's a reason it's called spin! I think what you're trying to get at is
that it can't be understood in the traditional context of an object spinning,
but the way that you're saying it is wrong.

~~~
likelynew
No, ELECTRON spin is not exactly a direction, as in 3D vector. In every
direction, it can be +1 or -1. It follows different transformation than a
vector(wigner matrix for j=1/2 and 1). Expressions like direction |z> and |x>
are not independent in this case.

Photon spin is actually a vector, as with all spin 1 particle.

