MIMO Terahertz Quantum Key Distribution

TL;DR

This paper introduces a MIMO quantum key distribution scheme for terahertz frequencies that enhances secret key rates and transmission distances, suitable for secure wireless communications at room temperature.

Contribution

It proposes a novel MIMO QKD scheme with beamforming that transforms the channel into multiple parallel lossy quantum channels, improving performance over single-antenna systems.

Findings

MIMO QKD outperforms single-antenna schemes in key rate and distance.

Multiple antennas are essential to counteract high THz free-space loss.

Positive key rates are achievable in the 10-30 THz frequency range.

Abstract

We propose a multiple-input multiple-output (MIMO) quantum key distribution (QKD) scheme for terahertz (THz) frequency applications operating at room temperature. Motivated by classical MIMO communications, a transmit-receive beamforming scheme is proposed that converts the rank-$r$ MIMO channel between Alice and Bob into $r$ parallel lossy quantum channels. Compared with existing single-antenna QKD schemes, we demonstrate that the MIMO QKD scheme leads to performance improvements by increasing the secret key rate and extending the transmission distance. Our simulation results show that multiple antennas are necessary to overcome the high free-space path loss at THz frequencies. We demonstrate a non-monotonic relation between performance and frequency, and reveal that positive key rates are achievable in the $10-30$ THz frequency range. The proposed scheme can be used for both indoor and outdoor QKD applications for beyond fifth-generation ultra-secure wireless communications systems.