Fix behavior of n_local calling circuits for num_qubits=1

[trigpolynom]

Summary

Fixes #13480.

When circuits that construct n_local were passed num_qubits = 1, an error would be thrown because the default entangling gate, "cx", requires at least 2. The fix involved just checking for num_qubits and setting to an empty array if num_qubits is not greater than 1.

Details and comments

The fix had to be applied to efficient_su2, excitation_preserving, and real_amplitudes. Test methods were added for each changed function.

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[Cryoris]

This approach looks good! I left some small comments, but you can do the same approach for the other functions (like real_amplitudes, ...) 🙂

[qiskit-bot]

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[Cryoris]

Thanks! There's also pauli_two_design which has the same issue 🙂

[trigpolynom]

Thanks! There's also pauli_two_design which has the same issue 🙂

oh shoot did not catch that sorry! Will put in fix tonight!

[Cryoris]

Thanks for the updates! The CI seems to be complaining the black should be run, otherwise this LGTM 👍🏻

[trigpolynom]

Thanks for the updates! The CI seems to be complaining the black should be run, otherwise this LGTM 👍🏻

should be good to go!

[qiskit-bot]

Thank you for opening a new pull request.

Before your PR can be merged it will first need to pass continuous integration tests and be reviewed. Sometimes the review process can be slow, so please be patient.

While you're waiting, please feel free to review other open PRs. While only a subset of people are authorized to approve pull requests for merging, everyone is encouraged to review open pull requests. Doing reviews helps reduce the burden on the core team and helps make the project's code better for everyone.

One or more of the following people are relevant to this code:

• @Cryoris
• @Qiskit/terra-core
• @ajavadia

[coveralls]

Pull Request Test Coverage Report for Build 12366380330

Details

• 12 of 12 (100.0%) changed or added relevant lines in 4 files are covered.
• 6 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.006%) to 88.967%

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Files with Coverage Reduction	New Missed Lines	%
crates/qasm2/src/lex.rs	6	92.98%

Totals
Change from base Build 12356117829:	0.006%
Covered Lines:	79436
Relevant Lines:	89287

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💛 - Coveralls

[Cryoris]

LGTM, thanks for the fix @trigpolynom!