ICTC 2026: Coherent Spatial Encoding for Crosstalk Mitigation in Free-Space Optical Quantum-MIMO Channels

Coherent Spatial Encoding for Crosstalk Mitigation in Free-Space Optical Quantum-MIMO Channels, by Shehbaz Tariq and Symeon Chatzinotas, will be presented at ICTC 2026, the 17th International Conference on ICT Convergence, held on 14–16 October 2026 on Jeju Island, Korea, and organized by the Korean Institute of Communications and Information Sciences (KICS).

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Abstract

Large-scale quantum communication over free-space optical (FSO) links is impaired by atmospheric turbulence, which induces spatial-mode coupling, aperture loss, and inter-rail crosstalk. In quantum multiple-input multiple-output (QuMIMO) systems, these effects simultaneously erase some photons by removing them from the collected modal subspace and redirect surviving quantum information from the intended receiver port to unintended ports, leading to an effective spatially correlated-erasure channel. The corresponding crosstalk and erasure statistics can be estimated from first-principles wave-optics simulations through the turbulent transfer matrix. Building on this channel characterization, this paper proposes a channel state information (CSI)-aware coherent spatial encoding scheme to improve correct-port transmission over turbulent QuMIMO links. The method encodes a polarization qubit into a rail superposition directed to one selected receiver port, using a principal eigenvector for fixed encoding or a matched filter for instantaneous CSI. The objective is to maximize the expected probability of arrival at the intended receiver port. The proposed scheme is benchmarked against best-rail transmission and approximate cloning. Numerical results from a passive phenomenological channel model show the benefit of instantaneous coherent spatial encoding under the specified receiver and fidelity conventions.