Reduced radical-pair signed-mixing sensitivity QA — 2026-10-08

Baseline main: 6e8e08d60f91526ca2c003b5db25a14ef76b4534.

The reduced signed S/T₀ frequency Hamiltonian uses diagonal entries −J/(2h), +J/(2h), and signed projected off-diagonal term v(B)=v0+(13.99624555 MHz/mT) Δg B /2. This is a selected matrix element, not a scalar addition law for full hyperfine and Zeeman Hamiltonians.

The previous Δg range [0,0.02] and nonnegative v0 excluded destructive cancellation for positive B. The revised Δg range [-0.02,0.02] and dedicated cancellation preset B=100 mT, J/h=10 MHz, Δg=−0.005, v0=3.5 MHz gives v(B)=0.0009386 MHz, gap 10.00000018 MHz, and hybridization 0.000003524%. Exact cancellation occurs near 100.0268 mT; the example lies within a single 5 mT B step of it. The v0 slider step was refined to 0.1 MHz so the preset is exactly representable.

Independent formula sweep: B in [0,5,20,100,250,500,1000] mT, exchange in [-60,-10,0,10,60] MHz, Δg in [-0.02,-0.005,0,0.005,0.02], v0 in [0,1,3.5,10,20] MHz: 875 cases, zero nonfinite outputs and zero hybridization fraction out of [0,1]. At exact J=v=0 the code defines the displayed fraction as zero by convention; the degenerate eigenstate mixing is not uniquely defined physically.

This is targeted source-level numerical QA, not a complete 73-control numerical/browser audit.