Abstract
The boundary-defined null connection (BDNC) framework identifies unsorted-marginal stability as the diagnostic location where any predictively distinct extension of standard quantum mechanics would have to depart, but stops short of supplying a BDNC-specific predictive law: a generic future-state weighting ansatz amounts to a no-signaling violation rather than a BDNC-specific signature. This paper supplies one candidate.
We propose the Null-Boundary Response postulate: in experiments with multiple coherent null alternatives and a future absorber boundary that partitions the channels, the joint source-absorber probability differs from standard quantum mechanics by a small response term proportional to the boundary-sensitive imaginary coherence between alternatives, antisymmetric across complementary absorber channels. The antisymmetry forces by construction, so no-signaling is preserved exactly: BDNC predicts no raw marginal violation.
We derive that the imaginary-coherence form falls out of a first-order expansion under a future-boundary-dependent path-dependent phase twist, and that the natural distinguishability window from the marker-induced reduction is , peaking at .
The experimental signature is a small in-quadrature phase-shift residual in the coincidence-difference fringe pattern of a phase-scanned delayed-choice quantum eraser, antisymmetric across complementary post-selection channels and invisible in the unsorted marginal. The signature carries a six-feature fingerprint that distinguishes it from generic no-signaling violation, ordinary decoherence, detector bias, and standard two-state-vector imaginary weak values.
We sketch the experimental protocol, identify basis-calibration as the principal systematic, and discuss what would constitute genuine confirmation versus confounding.