Impact of Entanglement Distillation on the Secret Key Rate of QKD Beyond Fidelity Enhancement

We examine how the structural characteristics of entangled quantum states impact the achievable rates in entanglement-based quantum key distribution (QKD). Focusing on the performance differences between entangled states produced by entanglement distillation protocols and Werner states, we show that the structured nature of distilled states can yield significantly higher secure key rates, even when their fidelity matches that of Werner states. This suggests that while converting arbitrary entangled states into Werner states (through twirling) simplifies the analysis of protocol performance, it also limits potential secret key rates. Our findings underscore the potential of entanglement distillation protocols to enhance QKD performance by additionally improving the structure of entangled states, thus, broadening their utility beyond simple fidelity enhancement.