Adaptive Entanglement Purification for Real–Time Quantum Noise Mitigation in Fiber–Optic Qubit Channels

We analyze an adaptive two-qubit purification protocol based on DEJMPS filtering for Bell pairs subject to combined amplitude-and phase-damping noise.A precomputed lookup table selects the optimal purification depth d and filter strength according to real-time single-qubit channel estimates ( , p).Monte Carlo simulations (T = 500 trials per (, p) grid point) over a 20 20 noise parameter sweep reveal that adaptivity yields nonzero fidelity gains F > 0 at a few, with an average positive F 0.83 at those points.These fidelity improvements occur in highly localized "islands" of moderate to high noise, and always incur a half-yield penalty Y = 0.5.We present 3D surfaces and 2D contour maps of F(, p) and Y (, p), alongside a representative table of the (, p) pairs with F = 0. Our results demonstrate that adaptivity provides significant fidelity boosts only in select noise regimes, informing when to trigger adaptive purification in practical quantum repeater and QKD deployments.