Efficient anomaly detection in a quantum network

A quantum network enables the execution of advanced protocols, such as distributed quantum computing, quantum metrology, quantum cryptography, and long-distance quantum communication. Anomalous nodes pose significant threats to these protocols, as they are notoriously difficult to detect and can cause severe disruption. In this work, we introduce a quantum-walk-based protocol for detecting such anomalies. The protocol exploits the sensitivity of coherent quantum transport to local perturbations of the network Hamiltonian. In particular, anomalous on-site potentials or modified hopping amplitudes alter the quantum walker's interference pattern, thereby shifting the time-averaged arrival probability between two trusted end points and offering the detection signal. We develop the protocol for one-dimensional quantum networks, derive spectral criteria for detectability, and discuss how the resulting ideas may extend to more general graph topologies.