✨ Implement Steane 7 Qubit Code

[adnathanail]

Description

Add 7-qubit Steane code as a benchmark

Fixes #813

Checklist:

• The pull request only contains commits that are focused and relevant to this change.
• I have added appropriate tests that cover the new/changed functionality.
• I have updated the documentation to reflect these changes.
• I have added entries to the changelog for any noteworthy additions, changes, fixes, or removals.
• I have added migration instructions to the upgrade guide (if needed).
• The changes follow the project's style guidelines and introduce no new warnings.
• The changes are fully tested and pass the CI checks.
• I have reviewed my own code changes.

[adnathanail]

@coderabbitai full review

[coderabbitai]

✅ Actions performed

Full review triggered.

[coderabbitai]

📝 Walkthrough

Summary by CodeRabbit

Release Notes

• New Features

  • Added 7 Qubit Steane Code benchmark for quantum circuit benchmarking.

• Tests

  • Added validation tests for the new benchmark across multiple scales.

• Documentation

  • Updated changelog with new benchmark entry.

Walkthrough

Adds a new benchmark implementing the 7-qubit Steane code (encoding, syndrome extraction, correction, decoding), registers it, updates tests for circuit structure and invalid sizes, and documents the change in the changelog.

Changes

Cohort / File(s)	Summary
Changelog CHANGELOG.md	Add Unreleased → Added entry for "7 Qubit Steane Code benchmark" and PR #814 reference.
Benchmark Implementation src/mqt/bench/benchmarks/seven_qubit_steane_code.py	New benchmark module providing create_circuit(num_qubits) that builds per-logical-qubit circuits (encoding, 13-qubit syndrome extraction with ancillas, conditional X/Z corrections, decoding), validates num_qubits % 13 == 0, composes multiple logical-qubit blocks, and registers the benchmark.
Tests tests/test_bench.py	Update SPECIAL_QUBIT_COUNTS to include "seven_qubit_steane_code": 13; add test_seven_qubit_steane_code_circuit_structure and parametric tests for valid sizes (13, 26, 39, 52) and invalid-size error message expecting divisibility by 13.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Suggested labels

mqt.bench

Suggested reviewers

• burgholzer

Poem

🐰 I hopped through circuits late at night,
Seven qubits dressed in error-correcting light,
Syndromes whispered, ancillas in line,
Xs and Zs danced to make the state fine,
Hooray — a benchmark, crisp and bright! 🎉

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly describes the main change: implementing the 7-qubit Steane code as a quantum benchmark.
Description check	✅ Passed	The PR description includes a summary, fixes reference (#813), and all checklist items are marked complete indicating thorough documentation and testing.
Linked Issues check	✅ Passed	The implementation successfully addresses issue #813 by implementing the 7-qubit Steane code with encoding, decoding, syndrome extraction, error correction, and registration as a benchmark.
Out of Scope Changes check	✅ Passed	All changes are directly related to implementing the 7-qubit Steane code benchmark: the new benchmark module, tests for the implementation, and changelog documentation.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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[coderabbitai]

Actionable comments posted: 2

🤖 Fix all issues with AI agents

In `@CHANGELOG.md`:
- Line 20: The changelog entry contains a duplicate hyphen breaking the list
formatting; locate the line containing "- - ⬆️ Increase minimum Qiskit version
to 2.0.0 ([`#803`]) ([**@adnathanail**])" in CHANGELOG.md and remove the extra
leading hyphen so it becomes a single list item "- ⬆️ Increase minimum Qiskit
version to 2.0.0 ([`#803`]) ([**@adnathanail**])".
- Around line 14-15: Add a changelog line for the 7‑qubit Steane code benchmark
in CHANGELOG.md similar to the existing entries; insert a line like "✨ Add
7‑qubit Steane code benchmark ([`#814`]) ([**@adnathanail**])" alongside the
existing Shor's 9 Qubit Code entry so the PR `#814` and the Steane benchmark are
recorded.

[adnathanail]

@coderabbitai full review

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✅ Actions performed

Full review triggered.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[adnathanail]

https://github.com/coderabbitai full review

[adnathanail]

@burgholzer @flowerthrower

[burgholzer]

This looks extremely clean as well. Pretty much the same comments as for your other PR also apply here.
I'd have a preference to first get the other PR merged and this one rebased after that.
This should be pretty much ready though! Very nice.

[adnathanail]

@burgholzer should be ready to go now!

[burgholzer]

Indeed. Very nice 🎉