Differential Phase Encoded Plug-and-Play Measurement-Device-Independent Quantum Key Distribution

Measurement-device-independent quantum key distribution (MDI-QKD) enhances security by removing vulnerabilities associated with detector side channels. Real-world implementations ofMDI-QKD face practical challenges, such as channel asymmetry and physical imperfections, which degrade the visibility of Hong&#x2013;Ou&#x2013;Mandel interference, an essential factor in determining the secure key rate. In this work, we evaluate the performance of differential phase encoded (DPE) MDI-QKD under realistic, asymmetric conditions. We analyze the effects of polarization and pulsewidth mismatches caused by channel asymmetry and identify tolerable limits for secure key generation. We introduce a plug-and-play DPE-MDI-QKD architecture that mitigates polarization fluctuations using Faraday mirrors and also compensates for pulsewidth mismatches. Furthermore, we propose an improved sifting scheme that raises the sifting efficiency from <inline-formula><tex-math notation="LaTeX">$\frac{4}{9}$</tex-math></inline-formula> to <inline-formula><tex-math notation="LaTeX">$\frac{2}{3}$</tex-math></inline-formula>, improving the secure key generation rates by 50&#x0025; and making it especially suitable for plug-and-play systems. These results offer practical insights into enhancing the robustness and efficiency of DPE-MDI-QKD, enabling more secure quantum communication over imperfect and asymmetric quantum channels.