An Interactive Introduction to Quantum Computing | Hacker News Reader

An Interactive Introduction to Quantum Computing

davidbkemp.github.io

254 pointskevlened22 comments

Interesting in this regard might also be the talk that Robert Smith of Rigetti Computing recently gave: 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

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...

Shor's algorithm: https://en.wikipedia.org/wiki/Shor%27s_algorithm

Grover's 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.)

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

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

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

> 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.

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.

> 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.

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.

The best introduction to this kind of computation that I've seen is Eric Johnston's SIGGRAPH 2016 talk[1], and the associated interactive simulator[2]. In the talk uses quantum superposition to implement a type of "quantum supersampling[3]".

[1] https://vimeo.com/180284417

[2] http://qcengine.com/

[3] https://en.wikipedia.org/wiki/Supersampling

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

In the second part and not explaining the principle.

I thought this was a pretty good introduction to quantum computing:

http://thinkingofutils.com/2017/12/quantum-computers/

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

You mean https://en.m.wikipedia.org/wiki/Quantum_machine_learning

why Hadamard of 1 is diffrent from Hadmard of 0?

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.

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.

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.

> 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.

From https://en.wikipedia.org/wiki/Spin_(physics):

>In quantum mechanics and particle physics, spin is an intrinsic form of angular momentum carried by elementary particles

And

>In some ways, spin is like a vector quantity; it has a definite magnitude, and it has a "direction" (but quantization makes this "direction" different from the direction of an ordinary vector).

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.

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.

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