[PR] [Feature] Add S gate to QuMat [mahout]

["tingyu-patrick (via GitHub)" <gi...@apache.org>]

tingyu-patrick opened a new pull request, #1540:
URL: https://github.com/apache/mahout/pull/1540

   ### Related Issues
   Part of #1511
   
   ### Changes
   
   - [ ] Bug fix
   - [x] New feature
   - [ ] Refactoring
   - [x] Documentation
   - [x] Test
   - [ ] CI/CD pipeline
   - [ ] Other
   
   ### Why
   
   `QuMat` currently has no S gate (phase of π/2), which is common in textbook circuits and standard transpilation targets. Users have to drop down to the underlying SDK to use it. This PR adds the S gate as one of the gates tracked in #1511 (one gate per PR, as requested there).
   
   ### How
   
   - Added `QuMat.apply_s_gate` in `qumat/qumat.py`, following the pattern of `apply_t_gate`.
   - Implemented it in all three backends: Qiskit, Cirq and Amazon Braket.
   - Added tests in `testing/qumat/test_single_qubit_gates.py` that run on all backends: basis-state preservation, S² = Z, S⁴ = I (each H-sandwiched so the phase becomes measurable), and a sign check (H-S-T-T-H ends in |1⟩, which would fail if the gate were S† instead of S).
   - Added an S-Gate section and an Updates entry to `docs/qumat/basic-gates.md`.
   
   All tests in `testing/qumat/` pass locally on all backends, and ruff passes. The ty and Rust pre-commit hooks could not run in my Windows environment (`uv` and `cargo` were not found by the hooks), so I am relying on CI for those.
   
   AI assistance: I used Claude to help draft the tests and docs. I reviewed and ran all of it and can explain every change.
   
   ## Checklist
   
   - [x] Added or updated unit tests for all changes
   - [x] Added or updated documentation for all changes


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Re: [PR] [Feature] Add S gate to QuMat [mahout]

["tingyu-patrick (via GitHub)" <gi...@apache.org>]

tingyu-patrick commented on PR #1540:
URL: https://github.com/apache/mahout/pull/1540#issuecomment-6525083795

   Hi @400Ping , sorry to bother you. When you have some free time, could you please take a look at this PR? Any feedback would be greatly appreciated!


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