MIMO Terahertz Quantum Key Distribution
This work addresses the challenge of secure wireless communications for beyond fifth-generation systems by enabling QKD at terahertz frequencies, though it appears incremental as it adapts classical MIMO techniques to quantum channels.
The paper tackles the problem of high free-space path loss in terahertz quantum key distribution (QKD) by proposing a MIMO scheme with transmit-receive beamforming, demonstrating performance improvements such as increased secret key rates and extended transmission distances, with positive key rates achievable in the 10-30 THz frequency range.
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.