{
  "artifact": "Density-matrix coherence laboratory",
  "chapter": "Density Matrices and Mixed States",
  "chapter_url": "https://www.steven-geller.com/playground/quantum/book/15-density-matrices-and-mixed-states/",
  "date_modified": "2026-08-14",
  "dependencies": [],
  "expected_exit_code": 0,
  "expected_stdout": "PASS: 15 density laboratory separates coherent/mixed X statistics by 0.500, tracks dephasing purities=[1.0000000000000004, 0.6250000000000002, 0.5000000000000002], and recovers Bell marginal purity=0.500\n",
  "fixture_sha256": "2f8230baacc2d1577dae0682d57834b8520f524282a8f4360925c00a4458fdfa",
  "manifest_test_command": "python3 tools/validate_briefs.py --briefs data/editorial_briefs_00_35.json --from 0 --through 35 --check-rewritten-sources --execute-artifacts",
  "pass_condition": "Fixtures compare coherent/mixed preparations in X and Z bases, verify PSD/trace, and recover maximally mixed marginals from a Bell state.",
  "python_requires": ">=3.11",
  "run_command": "python3 fixture.py",
  "schema_version": "1.1.0",
  "test_method": "Run the isolated fixture; require exit code 0 and exact stdout."
}