Vqe setup

[teaguetomesh]

Added a README to the Z2-VQE directory to help document where the code that implements certain functions can be found. I listed out the main components we will need for the full VQE experiment and tried to reference where the relevant functions are currently living. (Can iterate on this and update it later if we restructure the code).

Also added a function to resource.py for measuring O_{n,n'} but waiting on fully implementing it until its been debugged. The debugging and testing can be found in Z2LGT_BQ_VQE.ipynb.

Side note: how would you (@tjstavenger-pnnl and @EllaCrane) prefer code to be merged into main? Should I continue making PRs from my personal fork? Additionally, if I am only touching code in tutorials/Z2-lattice-gauge-theory perhaps it might make sense to split the VQE project into its own repo? Happy to hear your thoughts.

[tjstavenger-pnnl]

My answer will be a bit vague, but I think the choice of PR into c2qa-qiskit vs maintaining your own repo/fork comes to if you think others in the community would make use of your work. If it should be shared independent of your work, then I say put it in c2qa-qiskit. If it is dependent on your work and not likely usable outside of what you are doing, then your own repo or fork may be best.

Right now I'd lean towards using the PR you've submitted and merging it into c2qa-qiskit. We don't have a large community yet and the library is still pretty small, so any additions can help us along.

Maybe if your work seems separate from the Z2 lattice surgery effort it may be better in its own Python notebook?

[teaguetomesh]

Thanks for the helpful comments @tjstavenger-pnnl, I think for this code the most important thing is that it's in a shared place for @EllaCrane and I. Happy to contribute the c2qa-qiskit if that's the easiest route.

Would you prefer that I merge these PRs myself, or wait till you've had a look and confirm the merge?

[tjstavenger-pnnl]

I fixed the (another?) resource.py compile error this morning in the main branch that was causing a build error here: https://github.com/C2QA/c2qa-qiskit/runs/6408017686?check_suite_focus=true

It looks like we have merge conflicts though (not from the resource.py).

[teaguetomesh]

Closing this since all of its changes were merged in #38