Implements a reverse_map() method for JordanWignerMapper().

[MarcoBarroca]

Summary

This implements a reverse_map() method in the JordanWignerMapper(). It allows users to go back from qubit operators into fermionic operators. Completes issue #255.

Also included a unit test.

Details and comments

Instead of using the implementation linked in issue #255 I modified it to use the FermionicOp object for the mapping. Seemed like it would be easier for anyone to understand the code. Both implementations are equivalent.

[CLAassistant]

All committers have signed the CLA.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[woodsp-ibm]

I see there are failures which are not of this change but due to a newly released pylint version - I created #1346 as this needs fixing outside of this PR to get CI running again and passing on the code that is already in main here.

[MarcoBarroca]

Sure, I'll fix the mypy error by pushing the complex inside FermionicOp.

[MarcoBarroca]

Included the pylint fixes in this PR. Hope that's'okay. Should fix #1346

[woodsp-ibm]

Included the pylint fixes in this PR. Hope that's'okay.

Would it be too much to ask if you could do them in a separate PR. I think we will need to get the same fixes onto the stable branch so would want to backport the PR. Given this PR introduces a new feature its not something we would backport - that is more for critical fixes where we can do a bug fix release to address things.

Of course once such a separate PR was merged, and the branch here updated, it would all pass.

[woodsp-ibm]

I'll let this run so we can check things anyway if you like. (Once you have a PR that has been merged here it will not longer need a maintainers approval to run - its just on the first PR)

[coveralls]

Pull Request Test Coverage Report for Build 8665226229

Details

• 38 of 40 (95.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.04%) to 86.795%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
qiskit_nature/second_q/mappers/jordan_wigner_mapper.py	38	40	95.0%
<!--	Total:	38	40	95.0%	-->

Totals
Change from base Build 8662422324:	0.04%
Covered Lines:	8821
Relevant Lines:	10163

---

💛 - Coveralls

[woodsp-ibm]

Sorry my bad in the suggestion, if you did not correct it was

:class:`JordanWignerMapper

should have been

:class:`.JordanWignerMapper` where it was a . not a second `

[MarcoBarroca]

@woodsp-ibm Let me know if you think the note is okay when you can.

[woodsp-ibm]

@mrossinek Can I get you to take a look at this too.

[MarcoBarroca]

Hey, just wanted an update here. Is there anything I should do about this still?

[woodsp-ibm]

The build errors with mypy are fixed by #1362, which is still open. As far as progressing this hopefully @mrossinek can take a look.