PolarisationCarrier

Polarisation encoding: misalignment from a frame rotation, not a knob

6/6 passed in 2ms

Test	What it does	Result
test_carrier_reduces	An undescribed frame has contrast exactly 1.0, pol_error returns the misalignment, and the polarisation link equals the plain one in rate, qber and gain.	✅ pass
test_contrast_composes	pol_error composes misalignment and frame rotation as contrasts, 1 - 2e = (1 - 2e_miss) C to 1e-14, not as summed error rates.	✅ pass
test_drift_link	Through q.Link a 50 mrad drift lifts the qber from 3.31% to 3.545% and keeps 0.898 of the key rate, reporting tracking, optics misalignment, derived misalignment and contrast as separate rows.	✅ pass
test_frame_guards	q.ReferenceFrame refuses an unknown model, a field the chosen tracking model does not consume, a free frame with no rate, and dispersion without a width.	✅ pass
test_pmd_link	PMD contrast is the field overlap sqrt(mode_overlap), not the intensity overlap, and the link scales DGD by sqrt(length) to 0.5 ps at 25 km and refuses PMD with no span.	✅ pass
test_tracking_matters	A 5 mrad tracked frame and a 0.1 rad/sqrt(s) free walk over 1 s differ over 100x in error rate, and free-walk contrast decays from 1 to 0 with the interval.	✅ pass