6G network requirements such as terabit rate, sub-millisecond latency and information-theoretic security beyond the current cryptographic level, with future development of quantum computers, necessitate a dedicated secure layer. Quantum Key Distribution (QKD) offers the promised physical security; however, the practical range for a direct-transmission QKD link is around 200km, after which fibre attenuation results in unusable key rates. In this paper, we present the Hybrid Quantum Repeater Network (HQRN)-a combination of rare earth doped Er: YSO quantum memory nodes and Low Earth Orbit (LEO) satellites to transmit cryptographic keys over 5000 km in the presence of no trusted node. Teleportation-based entanglement swapping over 50 km fibre segments is used to remove the trusted-relay requirement. Using simulations performed using QuTiP and calibrated against experimental values obtained at the KIT Coimbatore 5G testbed, we achieve a stable secret key rate of 1.5 kbps and entanglement fidelity >82% over ten repeater nodes and an end-to-end latency of 48ms under a 1000-node IoT load. Simulation source code and original simulation outputs can be downloaded from GitHub at (https://github.com/abimanivasgam129-design/hqrn-simulation-). The results presented here can serve as the backbone of the Indian National Quantum Mission and provide technical details of a quantum network layer for 3GPP Release 20. Key physical parameters are found to be robust through sensitivity analyses simulating realistic deployment variations. Details on a NISQ implementation of QAOA routing with prescribed depth and mapping are presented. A hybrid QKD/CRYSTALS-Kyber scheme showing synchronised keys and a satellite-to-fibre transfer are provided.

Quantum Key Distribution (QKD;Hybrid Quantum Repeater Network (HQRN);6G security