Add from_openfermion function for fermionic operators

[ddhawan11]

Context:
Added function to convert openfermion fermionic operator to pennylane fermionic operators

Description of the Change:
This function converts openfermion FermionOperator object to pennylane FermiWord and FermiSentence objects

Benefits:
Easier integration between pennylane and openfermion

Possible Drawbacks:

Related GitHub Issues:

[ddhawan11]

[sc-62839]

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.67%. Comparing base (cdc36bc) to head (762e112).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5808      +/-   ##
==========================================
- Coverage   99.68%   99.67%   -0.01%     
==========================================
  Files         420      421       +1     
  Lines       40170    39893     -277     
==========================================
- Hits        40042    39763     -279     
- Misses        128      130       +2     

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[trbromley]

Thanks @ddhawan11, this looks great!

One question, could we make the functionality available at the top level? qml.from_openfermion()?

[trbromley]

Are we waiting on this PR before we finalize #5773?

[soranjh]

Are we waiting on this PR before we finalize #5773?

No, these two PRs are independent, but complement each other.

[soranjh]

Thanks @ddhawan11, looks good overall. Can we directly construct the objects as I suggested in the code?

[trbromley]

Thanks @ddhawan11, looks good overall. Can we directly construct the objects as I suggested in the code?

@soranjh I asked this because I see both PRs working on from_openfermion functions. But is the subtlety that #5773 works on qml.from_openfermion and this PR works on qml.qchem.from_openfermion? I'm wondering if this makes sense, and whether it could work to have the same qml.from_openfermion function work for both usecases.

[ddhawan11]

Thanks @ddhawan11, looks good overall. Can we directly construct the objects as I suggested in the code?

@soranjh I asked this because I see both PRs working on from_openfermion functions. But is the subtlety that #5773 works on qml.from_openfermion and this PR works on qml.qchem.from_openfermion? I'm wondering if this makes sense, and whether it could work to have the same qml.from_openfermion function work for both usecases.

@trbromley The difference between two functions is that this one converts Openfermion fermionic operator to PennyLane operators whereas the other PR works on converting openfermion qubit operators to PennyLane operators. I hope this helps.

[soranjh]

Thanks @ddhawan11, looks good overall. Can we directly construct the objects as I suggested in the code?

@soranjh I asked this because I see both PRs working on from_openfermion functions. But is the subtlety that #5773 works on qml.from_openfermion and this PR works on qml.qchem.from_openfermion? I'm wondering if this makes sense, and whether it could work to have the same qml.from_openfermion function work for both usecases.

@trbromley We should have two functions qml.from_openfermion and qml.to_openfermion. I will make sure both PRs work this way. Just a note that the functionality in these PRs are NOT duplicated; what we have here is not added there.

[Jaybsoni]

Nice work 💯! Looks good to me, just a few comments to address

[trbromley]

Thanks @ddhawan11, looks good overall. Can we directly construct the objects as I suggested in the code?

@soranjh I asked this because I see both PRs working on from_openfermion functions. But is the subtlety that #5773 works on qml.from_openfermion and this PR works on qml.qchem.from_openfermion? I'm wondering if this makes sense, and whether it could work to have the same qml.from_openfermion function work for both usecases.

@trbromley We should have two functions qml.from_openfermion and qml.to_openfermion. I will make sure both PRs work this way. Just a note that the functionality in these PRs are NOT duplicated; what we have here is not added there.

Thanks! Ok, I'll hold off on reviewing this PR until it's ready.

[soranjh]

Thanks @ddhawan11, looks good overall. Can we directly construct the objects as I suggested in the code?

@soranjh I asked this because I see both PRs working on from_openfermion functions. But is the subtlety that #5773 works on qml.from_openfermion and this PR works on qml.qchem.from_openfermion? I'm wondering if this makes sense, and whether it could work to have the same qml.from_openfermion function work for both usecases.

@trbromley We should have two functions qml.from_openfermion and qml.to_openfermion. I will make sure both PRs work this way. Just a note that the functionality in these PRs are NOT duplicated; what we have here is not added there.

Thanks! Ok, I'll hold off on reviewing this PR until it's ready.

@trbromley This PR (5808) is ready for your review right now.

[soranjh]

Thanks @ddhawan11, one minor comment on using a full name for openfermion_op and then good from my side.