[Walther]

Thank you for feedback! Going to read the paper to improve my understanding. I'm writing this blog series in part to learn more - both about quantum computing as well as Rust. As some people say, teaching is a great way to learn (or at least check your knowledge).

What do you think would be a good correction or disclaimer to add? Would it be sufficient to e.g. say that in this first part, we only implement a two-component ket? Generalizing the ket type to an arbitrary-size vector while keeping type constraints, perhaps briefly mentioning const generics (an upcoming language feature), etc could easily make for another part in this series. Making the ket into an actual vector could then give way to doing proper linear algebra on them, cleaning up some of the manually implemented operations here, as their teaching purpose has been fulfilled already.

Thoughts?

[reikonomusha]

I would say you’ve implemented a state vector for a single qubit (when the norm = 1 and when equality is defined to be phase invariant, i.e., x and y are equal whenever there’s an ‘a’ such that e^(ia)x = y.), which can be written down notationally with a ket:

|s> = p|0> + q|1>

where p and q are complex, and |p|^2 + |q|^2 = 1. The ket is the notation |s>, |1>, and |0>, which could also be written purely as column vectors.

At the end it all depends on what you want to present. What will be the climax? Unitary evolution of a pure state? Superoperators on a mixed state? An introduction to linear algebra used in quantum computation and its notation?

In any case I’d present what a quantum state is on N qubits, which requires 2^N-element complex vectors that satisfy a few properties.

[eigenloss]

Having "quantum computing" in the title makes this genuine clickbait when the body lacks any explanation of what a state is or what a ket is. Energy or momentum or spin states are rarely (never, in reality) just numbers.

You made no attempt to explain what the two different states in a single ket mean: hint, it's superposition. Never provided even a trivial justification for why normalization is important; where is the actual physics?

Using Rust here is also quite pointless when you're just doing linear algebra... where is the actual benefit over Python or even Haskell?

You've written a very cute and inefficient math library, but calling this QC is just false advertising.

[Walther]

Thank you for your feedback!

You're right, the essay needs a better explanation on what a ket and a quantum state is. I'll figure something out.

Excellent point with the superposition, I'll add that in! Same with the normalization - while adding the `is_valid` method to the struct makes sense programming story -wise, it'd be great to justify its origins and implications.

As for using Rust being pointless - I am writing this blog post series for three reasons: learning more Rust by doing, learning more quantum computing by doing, and sharing my journey as a tutorial. Using Rust for the sake of learning (and hopefully helping others learn) Rust is in my opinion a perfect reason to use Rust.

As for calling this QC - I'd clarify that this code does not intend to be a production-grade QC library, and the blog post series does not intend to be an exact, axioms-and-proofs type of an university level course that prepares you for the industry in one go. I'd think of it more as a Todo MVC app building journey with a quantum flavor - or something. That being said, I do plan to add more QC features in the next posts of the series, and incrementally add to the accuracy as much as I feasibly can. All this feedback here and links to more materials are helping me immensely, I want to learn more about this stuff!

Thank you for calling it very cute - I really appreciate that! ️

[eigenloss]

McIntyre or Griffiths' QM might be useful.