Background.md draft

[johnzl-777]

This is admittedly sparser than I would hope and should certainly go under further revisions but there are two things I'm thinking of adding:

1. @plquera has done a lot of work explaining similar things in his qbook. I'm inclined to provide links to the relevant sections for any newcomers who want a deeper explanation.
2. I don't really have any code examples and I'm uncertain if this is the right place to put them. Would the docstrings of things like .rydberg and .rabi be a better place?

I also had a talk with @weinbe58 and he thought it best not to really mention .hyperfine considering it's not very actively shown/talked about.

[github-actions[bot]]

PR Preview Action v1.4.7 :---: Preview removed because the pull request was closed. 2024-05-30 15:45 UTC

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 89.91%. Comparing base (d627b19) to head (3efdb29).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #962 +/- ## ======================================= Coverage 89.91% 89.91% ======================================= Files 110 110 Lines 8129 8129 ======================================= Hits 7309 7309 Misses 820 820 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[Roger-luo]

This sounds good to me; we don't need to be very detailed here; we can direct things to @plquera's book in the background section. All we need is a quick explanation of the acronyms and equations (e.g., what we are simulating/running).

PS. I forgot to mention that the main purpose of this is to give a quick explanation when a user sees a physics acronym in other parts of the documentation. So ideally, we want to cover a wider range of concepts but not go into the details here. Then you can guide people to read the book (or other references) for more explanation

[johnzl-777]

Sounds good! I think the topics the background covers so far are the ones that we expect to link back to the revised index.md and quick_start.md. More than willing to add more if you think these topics are currently not enough.

I went ahead and put references towards the qbook. In the spirit of keeping things short in the background I imagine the docstrings, (when we get to revising them) will provide more detail as to how exactly to accomplish what's defined in the background (e.g. non-uniform local control).

[Roger-luo]

are we adding the links to background in quick start in this PR or next PR? the content itself LGTM

[johnzl-777]

I'll add the links in this PR (: I don't think that will cause the PR to be too large for reasonable review