Toward Fault-Tolerant Quantum Mesh Networks

Abstract

We propose a decentralized mesh architecture for quantum key distribution (QKD) that tolerates node failure rates up to 34% without trusted relays, using entanglement swapping over redundant lattice paths. This paper describes the protocol, our simulation methodology, and preliminary benchmarks from a 12-node laboratory testbed.

1. Introduction

Quantum networks today depend on trusted relay nodes — a fundamental compromise. Each relay is a surveillance point, a failure domain, and a cost center. The architecture we describe here removes the trusted relay entirely, replacing it with a mesh of semi-honest nodes that route entanglement the way the internet routes packets.

The implications extend beyond cryptography. A fault-tolerant quantum mesh is a prerequisite for distributed quantum computing, blind quantum computation as a service, and verifiable delegated sensing.

2. Lattice Path Redundancy

The core insight is borrowed from percolation theory: in a sufficiently connected lattice, there is no single cut that partitions the network. We arrange nodes on a hexagonal lattice where each node maintains entanglement links with six neighbors.

When a node fails or is compromised, the routing layer recomputes entanglement-swap paths around the failure within two heartbeat intervals (approximately 400 ms in our testbed). Security does not degrade because no node ever holds enough information to reconstruct a key.

3. Simulation Results

We simulated 10,000 attack-and-failure scenarios across lattice sizes from 12 to 1,024 nodes. Key findings:

• Key generation throughput degrades gracefully: 50% node loss reduces throughput by only 61%, versus total collapse in trusted-relay topologies.
• The 34% failure tolerance threshold emerges sharply at lattice sizes above 48 nodes.
• Adversarial nodes contribute zero information gain beyond the quantum bit error rate baseline.

4. Laboratory Testbed

Our 12-node benchtop system uses spontaneous parametric down-conversion sources and superconducting nanowire detectors. Over 72 hours of continuous operation, the mesh sustained a secure key rate of 1.2 kbps with three nodes deliberately faulted.

5. Conclusion

Trusted relays were a scaffolding, not a foundation. Mesh-native quantum networking is practical with today's photonics, and the protocol described here is released into the public domain. Supporters of the TechNow fund directly finance the 64-node expansion planned for next year.

References

1. Elliott, C. Building the quantum network. New J. Phys. 4, 46 (2002).
2. Acín, A. et al. Device-independent security of quantum cryptography. Phys. Rev. Lett. 98, 230501 (2007).