Dynamic RIS-Assisted THz Quantum Networks: Joint Optimization of Entanglement Generation and Fidelity under Channel Impairments

TL;DR

The paper tackles entanglement distribution over THz wireless links by introducing a dynamic RIS that switches between active and passive modes to counter THz impairments and misalignment. It develops a quantum-aware THz channel model and a joint optimization framework that selects RIS placement, initial entanglement generation rates, and RIS mode patterns to maximize end-to-end entanglement throughput while meeting fidelity and fairness constraints. Security considerations are integrated by analyzing side-channel leakage from dynamic RIS switching and proposing mitigations such as randomized RIS activation and secure QKD protocols. Simulation results show substantial fidelity and fairness improvements over static RIS baselines and demonstrate robustness under realistic THz channel conditions, underlining the practicality of dynamic RIS for scalable quantum communications.

Abstract

Quantum networks (QNs) supported by terahertz (THz) wireless links present a transformative alternative to fiber-based infrastructures, particularly in mobile and infrastructure-scarce environments. However, signal attenuation, molecular absorption, and severe propagation losses in THz channels pose significant challenges to reliable quantum state transmission and entanglement distribution. To overcome these limitations, we propose a dynamic reconfigurable intelligent surface (RIS)-assisted wireless QN architecture that leverages adaptive RIS elements capable of switching between active and passive modes based on the incident signal-to-noise ratio (SNR). These dynamic RIS elements enhance beamforming control over amplitude and phase, enabling robust redirection and compensation for THz-specific impairments. We develop a detailed analytical model that incorporates key physical layer phenomena in THz quantum links, including path loss, fading, thermal noise, and alignment variations. A secure optimization framework is formulated to jointly determine RIS placement and entanglement generation rate (EGR) allocation, while satisfying fidelity, security, and fairness constraints under diverse quality of service (QoS) demands. The model also includes an exploration of side-channel vulnerabilities arising from dynamic RIS switching patterns. Simulation results demonstrate that the proposed architecture yields up to 87\% fidelity enhancement and 65\% fairness improvement compared to static RIS baselines, while maintaining robustness under realistic THz channel conditions. These results underscore the promise of dynamic RIS technology in enabling scalable and adaptive quantum communications over wireless THz links.

Figures (6)

• Figure 1: System model.
• Figure 2: System-level diagram illustrating dynamic RIS-assisted quantum signal routing, where RIS adaptively switches modes based on signal strength to enhance fidelity and entanglement.
• Figure 3: Jain’s fairness index comparison among proposed, rate-maximizing, and log-rate maximizing schemes under three user placement scenarios.
• Figure 4: Impact of environmental turbulence on the total end-to-end sum rate for the dynamic RIS-assisted quantum network.
• Figure 5: Simulation results illustrating the impact of turbulence, THz fading, and dynamic RIS on E2E quantum network performance. (a)--(b): Rate loss under moderate/strong turbulence. (c): Tradeoff between fidelity and rate. (d): RIS element scaling benefits. (e): Distance-induced rate decay under THz. (f): Photon success vs. RIS height. (g): RIS mode comparison. (h)Quantum-aware THz capacity declines with range.