Qiskit integration in C3 optimal control workflows

[lazyoracle]

What

Further integration of qiskit interface with the c3 optimal control workflows

Why

Closes #166

How

• Provide user access to get and set the experiment object used inside the c3.qiskit backend for running physics simulations
• Add examples and documentation on typical usage of qiskit circuits for visualisations during optimal control workflows

Remarks

Please check the notebooks in examples/, specifically the two_qubit_entangling_gate.ipynb for a detailed demonstration of how one can run qiskit circuits while optimizing gates.

Checklist

Please include and complete the following checklist. Your Pull Request is (in most cases) not ready for review until the following have been completed. You can create a draft PR while you are still completing the checklist. Check the Contribution Guidelines for more details. You can mark an item as complete with the - [x] prefix

• [x] Tests - Added unit tests for new code, regression tests for bugs and updated the integration tests if required
• [x] Formatting & Linting - black and flake8 have been used to ensure styling guidelines are met
• [x] Type Annotations - All new code has been type annotated in the function signatures using type hints
• [x] Docstrings - Docstrings have been provided for functions in the numpydoc style
• [x] Documentation - The tutorial style documentation has been updated to explain changes & new features
• [x] Notebooks - Example notebooks have been updated to incorporate changes and new features
• [x] Changelog - A short note on this PR has been added to the Upcoming Release section

[codecov[bot]]

Codecov Report

Merging #169 (ee7597c) into dev (e2e7add) will increase coverage by 0.08%. The diff coverage is 93.93%.

@@            Coverage Diff             @@
##              dev     #169      +/-   ##
==========================================
+ Coverage   72.48%   72.57%   +0.08%     
==========================================
  Files          37       37              
  Lines        5531     5556      +25     
==========================================
+ Hits         4009     4032      +23     
- Misses       1522     1524       +2     

Impacted Files	Coverage Δ
c3/libraries/constants.py	100.00% <ø> (ø)
c3/qiskit/c3_backend.py	90.04% <93.93%> (+0.26%)	:arrow_up:

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[lgtm-com[bot]]

This pull request fixes 1 alert when merging ee7597c2bbb01eece9fc1de2cb312b2f791c5896 into e2e7adddaded6111640f57d2d9f23bee00d03378 - view on LGTM.com

fixed alerts:

• 1 for Unused local variable