Discord-Enhanced Quantum Key Distribution in Noisy Mixed-State Channels

Quantum key distribution (QKD) facilitates secure communication by harnessing non-classical correlations within quantum systems. Although entanglement is fundamental to many QKD protocols, it is highly susceptible to noise and decoherence effects. In this work, we analyze the performance of Werner and Bell-diagonal states within commonly used QKD protocols such as BB84, Six-state, and their device-independent variants, considering realistic noise environments and eavesdropping strategies. Employing a Qiskit-based simulation toolkit , we assess critical performance metrics including quantum bit error rate (QBER), fidelity, concurrence, quantum discord, violations of the CHSH inequality, and Devetak, Winter key rates. Our findings emphasize the resilience of quantum discord as a resource in scenarios where entanglement is diminished, and reveal that Bell-diagonal states may exhibit superior performance compared to Werner states under certain noise conditions. We further discuss practical consequences for secure key generation and propose directions for extending this work toward physical device implementation and machine learning–enhanced detection of eavesdropping attempts. These results shed light on the robustness of QKD protocols that utilize mixed quantum states and the significant role quantum discord can play in secure quantum communication.