Multiple-Antenna Continuous-Variable Quantum Cryptography

Continuous-variable (CV) quantum key distribution (QKD) in optical multiple-antenna settings can be useful in harsh channel conditions despite the presence of cross-talk between channels. This is, for instance, relevant to satellite-based QKD with multiple transmitting antennas on the satellite and multiple ground stations. In such a case, each transmitter independently exchanges data with its intended receiver, where the received signal may contain components from other transmitters. In particular, for a 2×2 multiple-input multiple-output (MIMO) setting with Gaussian encoding and heterodyne detection, preliminary key rate analysis has recently been presented and compared with single-mode and multiplexed CV-QKD scenarios. In this work, we study the effect of different MIMO channels on the performance by accounting for the cross-talk parameter in slow fading channels.