Working version of the old tomography tutorial

[gadial]

Summary

This PR returns to qiskit-tutorials the tomography tutorial that was once part of it, but was removed due to run failures.

Details and comments

This version should work with the most up-to-date version of Qiskit, given a correct installation of cvxpy, which means it was correctly linked with blas and lapack; othewise running will result in an error about the SCS engine being unable to solve SDP's.

[nonhermitian]

Seems like the original issue still occurs here as it is failing with a SCS error.

[gadial]

Seems like the original issue still occurs here as it is failing with a SCS error.

Unfortunately that's not the original issue (which was state_fidelity failing due to missing validate=False argument) but something new and much more troublesome which affects Ingis in general.

[chriseclectic]

You need to install cvxopt in the doc build environment (@mtreinish)

[nonhermitian]

There are some formatting issues in the rendered docs:

Also not sure about this:

[gadial]

There are some formatting issues in the rendered docs:

I fixed the rendering issue. As to the "FATAL: cannot solve SDP", sadly this is the expected behavior - currently Ignis performs a test run to check whether some engine can be used; if it cannot, it uses another, but in the process this "FATAL" message is sent. We need to fix this inside Ignis itself.

[nonhermitian]

It seems that the PR includes changes to 21 different files. Can this be trimmed down to include only the tomography tutorial. Otherwise, a list of changes to the other files should be given as well. Otherwise, the tomo one looks good to go.

[gadial]

It seems that the PR includes changes to 21 different files. Can this be trimmed down to include only the tomography tutorial. Otherwise, a list of changes to the other files should be given as well. Otherwise, the tomo one looks good to go.

This is due to some rebase problem I couldn't fix. I think I'll have to create a new PR with the fixed notebook.