Resurrecting Coherence: An Open-Source Pipeline for Zero-Noise Extrapolation and Dynamical Decoupling

I applied gate‑level XY4 after the entanglement. The immediate observation was that the parity signal stayed positive for slightly larger qubit counts—the DD was doing something. However, the overall fidelity improvement was minimal: at best a 1% absolute increase for 4 and 8 qubits, and no gain for 16 qubits and above. The DD simply cannot combat the dominant error: two‑qubit gate noise. Every CNOT gate introduces an error of around 1–2%, and for an 80‑qubit GHZ state, there are 79 CNOTs in series. The cumulative error overwhelms any phase‑refocusing benefit.