Distributing Entanglement Over Quantum Networks for Sensing Applications

Abstract

Quantum networks enable the distribution of entangled states across spatially separated nodes, enabling cutting-edge technologies such as quantum communication, distributed quantum sensing, and computation. As these networks mature, it becomes increasingly important to understand how entanglement can be delivered and used most efficiently under realistic physical constraints. This thesis investigates the end-to-end utility of entanglement distributed by quantum networks, with a focus on sensing applications, bridging network-level protocol design with application-specific performance metrics. We introduce a multi-path entanglement routing protocol leveraging time-multiplexed repeaters with local knowledge. We employ simulations across various network topologies to characterize how consumer placement and contention influence the utility of dynamic distance based and static path based routing strategies. Our results determine the optimal duration of allocated time slots depending on the quantum memory coherence time. We next evaluate the benefit of entangled states for parameter estimation. We introduce immediate sensing, fixed-block, and variable-block length multiplexing protocols for preparing and using entangled probe states and compare the average quantum Fisher information (QFI) of each. We identify fidelity thresholds above which GHZ-state-based strategies outperform product states and show how distillation can amplify this advantage. We also design a practical measurement strategy that preserves the advantage of entanglement without requiring expensive global measurements. We then analyze the impact of entanglement in hypothesis-testing settings. In the ideal regime, GHZ entangled states offer a linear advantage in time-to-discrimination with the number of sensors. Under realistic noise models, we derive performance bounds using the Helstrom and Chernoff distances and identify operating regimes where entanglement provides a tangible advantage. We characterize the performance interplay of fidelity, exposure time, and qubit coherence time. We show that entangled states can help systems suffering from decoherence by reducing the necessary exposure time of qubits. Our findings highlight that entanglement is not universally beneficial. Its utility depends on the interaction between network noise, resource constraints, and application. By combining insights from entanglement distribution and quantum sensing, this work provides a foundation for optimizing the deployment and management of quantum resources in future quantum networks.