quantum-capacity

Exact quantum capacities under partial environmental observation and joint-register degradation. Includes optimal photon counting over all predetermined individual helper measurements in a qubit loss model, a strict collective-measurement rate advantage, and energy limits for vacuum optical splitting.

Proofs and reproducible certificates for geometric conditions that yield zero optimized single-use coherent information but positive quantum capacity in flagged qubit channels with noisy measurement records, including a certified eight-use witness.