Fix inverse() on circuits containing initialize() to raise CircuitError early

[macatizm]

Fixes #15595

Previously, calling inverse() on a circuit containing initialize() would crash with a misleading internal error about invalid param types when trying to construct the inverse gate. This happened because Initialize has a definition (via _define()), so it passed the base Instruction.inverse() check, but then failed later during gate construction.

Now, Initialize.inverse() explicitly raises CircuitError early with a clear message, similar to how reset() behaves. This provides a better user experience with an informative error message instead of an internal error.

The fix adds an inverse() method to the Initialize class that immediately raises CircuitError, explaining that initialize is a non-unitary instruction and cannot be inverted.

Changes

• Added inverse() method to Initialize class that raises CircuitError early
• Added import for CircuitError exception
• Error message follows the same pattern as other non-invertible instructions (e.g., PauliProductMeasurement)

Testing

The fix prevents the following error:

CircuitError: "Invalid param type <class 'complex'> for gate initialize_dg."

And instead raises:

CircuitError: "inverse() not implemented for initialize. initialize is a non-unitary instruction and cannot be inverted."

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

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

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
1 out of 2 committers have signed the CLA.

✅ macatizm
❌ Gittensor Miner

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[Cryoris]

Thanks for the contribution! Could you add a test and a release note (under fixes) for this?

[macatizm]

Hi, @Cryoris
I updated initializer.py file and added test and release note.

[coveralls]

Pull Request Test Coverage Report for Build 21386925525

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

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• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 3 of 3 (100.0%) changed or added relevant lines in 1 file are covered.
• 15 unchanged lines in 5 files lost coverage.
• Overall coverage decreased (-0.008%) to 87.982%

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Files with Coverage Reduction	New Missed Lines	%
crates/circuit/src/parameter/parameter_expression.rs	1	87.17%
crates/transpiler/src/passes/unitary_synthesis/decomposers.rs	1	96.02%
crates/circuit/src/parameter/symbol_expr.rs	2	73.24%
crates/qasm2/src/lex.rs	5	91.77%
crates/qasm2/src/parse.rs	6	97.63%

Totals
Change from base Build 21365885240:	-0.008%
Covered Lines:	100086
Relevant Lines:	113757

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💛 - Coveralls

[ShellyGarion]

thanks for your contribution to qiskit @macatizm
any idea why the CLA has not been properly signed? #15607 (comment)

[ShellyGarion]

The CLA was not signed properly since the commits were made by Gittensor Miner.

[jakelishman]

I believe this may have been LLM generated without attribution. Please confirm the model used, and that the PR was tested and checked by a human before submission.

I also see that this is being done for some sort of bug bounty. Qiskit did not sign up for this bug bounty and does not endorse it. We welcome quality contributions from humans, but not externally incentivised AI spam.