Multimode non-Gaussian secure communication under mode-mismatch

In this paper, we analyse the role of non-Gaussianity in continuous-variable (CV) quantum key distribution (QKD) with multimode light under mode-mismatch. We consider entanglement-based protocol with non-Gaussian resources generated by single-photon-subtraction and zero-photon-catalysis on a two-mode squeezed vacuum state (TMSV). Our results indicate that, compared to the case of TMSV, these non-Gaussian resources reasonably enhances the performance of CV-QKD, even under the effect of noise arising due to mode-mismatch. To be specific, while in the case of TMSV the maximum transmission distance is limited to 47 Km, single-photon subtracted TMSV and zero-photon-catalysed TMSV yield much higher distance of 73 Km and 152 Km respectively. However, photon loss as a practical concern in zero-photon-catalysis setup limits the transmission distance for zero-photon-catalysed TMSV to 36 Km. This makes single-photon-subtraction on TMSV to be the best choice for entanglement-based CV-QKD in obtaining large transmission distance. Nonetheless, we note that the non-Gaussianity does not improve the robustness of entanglement-based CV-QKD scheme against detection inefficiency. We believe that our work provides a practical view of implementing CV-QKD with multimode light under realistic conditions.