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Hi all!

I have an idea for a series of 3 posts on quantum community detection:

- Quantum superposition vs statistical mixtures (draft here + some notes on the next parts)
- Community detection in (classical) complex networks
- Quantum community detection

First two topic are standalone, general introduction to these topics. And I believe that they are of the general interest and benefit of the readers. The third one is about a paper arXiv:1310.6638, in which we are trying to predict the scale of quantum effects in a light-harvesting complex of green plants. It is an investigation in the same team (Jake Biamonte, Tomi Johnson and Mauro Faccin, Ville Bergholm and me) as the previous quantum network posts:

John, what do you think about it?

That is, is the concept of these blog post nice? Do you like the introduction to quantum superposition?

## Comments

I'm happy to help edit your posts if John is happy to let us invade his amazing blog with quantum physics! The quantum bio stuff fits in and probably people want to know more about quantum stuff in general, which is why your first article on quantum states would likely be well received.

Just a side comment (LHCII is for you only a special application for your methods, so this is probably not so interesting for you):

Some community detection for you: There is another community mostly located in Arizona, which used serial time resolved investigations with femtosecond X-ray lasers of PSI. I don't have access to all those papers from them and [28] from the Fleming group and frankly also not the time to study them in detail, but it might be that there are still discussions about the concrete topology of the involved electron transfer channels. That is I was in particular irritated by one image (which is now shunned from public access), which somehow suggested another interpretation of the role of chlorophyll a. That is in the image it looked (if I remember correctly) as if chlorophyll a is sort of parallel to P680 (they seem to operate in different wavelengths (do they?)) in the transfer chain to pheophytin, however Wikipedia writes that

unfortunately Wikipedia contradicts itself by claiming also (a bit down the page) that chlorophyll a IS P680, which seems wrong since P680 is a dimer and it looks as if chlorophyll a is not (?)

Links to the article and similar research here

Hi!

Piotr wrote:

That sounds like a nice series! Please go ahead and write these posts... and please get Jacob Biamonte to edit the English, as I just did here. Then I'll edit his English, and by the end it will be okay.

There will be some people interested in learning about quantum superpositions, and others who know quantum mechanics interested in hearing how it's important in photosynthesis, so you'll have a fun challenge writing to multiple audiences. One good trick is to make sure the beginning of each post is easy, but then, if there's more advanced stuff, include it at the end with some warning like "Experts might be interested to hear that..."

Quantum mechanics is not really one of the main foci of Azimuth, but it's fun. Photosynthesis and the capture of solar energy really

dofit into the main focus of Azimuth, so the more you can say about those topics, the better!Hi John,

it is great to hear that you like it!

English - sure. When I read my stuff a few days after writing it, I can spot so many mistakes (except for articles, which are still a bit tricky for me).

With quantum mechanics - I know it is not the main focus of Azimuth, so my biggest doubt is what should be the level. Do you think that, as of now, it is OK?

Hi Piotr,

I don't think there's any description of how to read quantum circuit diagrams on the Azimuth wiki. I'd need one :).

Hi Jim,

quantum circuits are another (and fascinating!) story. If there is need, I can write such (though, there are many much more competent persons to write it).

In general, there is an interesting notation of Penrose for tensors, which is often used (sometimes implicitly) in quantum many-body systems.

I think that formalising and explaining as many useful diagramming conventions as possible is an Azimuth goal. Do you know any good descriptions of quantum circuit diagrams, The Wikipedia entry is cursory and searching didn't come up with anything useful. How these relate to the Penrose notation which I could just about grasp in the Emperor's new clothes. I don't think that there's a guide to ladder diagrams which had struck me as another omission which I'm not the best person to write either.

I guess it's also off topic wrt. clustering techniques but I'd also like to know about how you specify applications for use with QIT?

Thanks for the reminder that Penrose notation exists.

Cheers

Piotr wrote:

The big challenge of science writing is to carefully imagine a class of readers and always make sure what you write is comprehensible to that class. It doesn't matter so much what the class is, as long as it's much larger than "me, myself, and I".

Can you tell me what class of readers you are trying to be comprehensible to?

Let's see if I can guess from what you write. You write:

$$ |\psi\rangle = \alpha |1\rangle + \beta |2\rangle \equiv \begin{bmatrix} \alpha \ \beta \end{bmatrix} $$ Someone who has taken a first course in quantum mechanics will understand the bra-ket notation here. Are you writing to that class of people? Or are you hoping that this equation will explain that notation to someone who has never seen it? That would be overoptimistic, I think.

A mathematically sophisticated reader might see that $\equiv$ sign, realize you're defining $|1 \rangle$ and $|2 \rangle$ by this equation, and take the vertical line and angle bracket in $1 \rangle$ to be undefined primitives. But most mathematicians who haven't seen bra-ket notation will wonder why you're writing things like $| 1 \rangle$ instead of $e_1$ for the standard basis vectors. They will have trouble believing that this vertical line and angle bracket are undefined primitives; they'll want to know the rules governing them. And later you spring the notation $|\psi \rangle$ on the reader, whose meaning cannot be guessed by knowing

$$ |1 \rangle = \begin{bmatrix} 1 \ 0 \end{bmatrix} $$ Quantum mechanics typically takes a year to learn and is considered difficult. So, almost nobody will be able to learn it from a single blog post. Maybe your audience is people who have taken a course on it, or tried to read a book on it, but need more practice?

Will this audience be able to understand the next posts in the series?

Often people overestimate the ability of others to keep up with a rapid ascent from basics to more advanced material. To avoid this problem, sometimes it can be better to choose a fairly sophisticated audience from the start, and write to them. But the main thing is to make a clear choice. It can be very good to say at the start of a post

who your intended audience is. If the second post is a lot harder than the first, say that. In a blog post you can do this in a jokey way, likeI do this kind of thing sometimes. It may sound cruel but it's less cruel than suddenly increasing the prerequisites without admitting it.

Hi John,

thank you for your remarks. A few times I thought quantum mechanics from scratch (http://migdal.wikidot.com/en:quantum-outlines), but you are right that even braket notation needs some time, before one understands it and get used to it. And if 'decypher my mathematical notation' is a puzzle, then it is not the most enjoyable kind of puzzle.

Braket - I will delete it (or elaborate carefully).

For other stuff - my goal is explain off-diagonal elements in density matrix. Within this constraint, I want to make it as accessible as possible. Some matrix calculus is necessary. Popular-science level of quantum mechanics as well. It

mightbe useful to be after some introduction to quantum mechanics, but I think it is not a requirement.In any case, I will change some stuff and test it on some smart friends, who are not physicists.