Enhancing Entanglement Distribution by Pre- and Post-Processing

Accomplishing many quantum information processing tasks requires the distribution of high-quality entangled states. Typically, this is done by distributing entangled photons to participating parties via optical fibers. However, such transmission necessarily introduces noise to the sent photons. Therefore, it is crucial to investigate strategies that enhance the quality of distributed entangled states. In this work, we propose an entanglement distribution protocol based on pre- and post-processing. Specifically, we theoretically benchmark the maximal entanglement fidelity achievable by sending Bell states through Pauli channels. Then we show that a GHZ encoding and post-selection based on parity measurements can achieve fidelity beyond the benchmark. To demonstrate the practicality of our protocol, we perform process tomography on single-mode fibers and compare the fidelities achievable with Bell states and with GHZ states. This demonstrates an efficient and simpler solution compared to other existing methods for dispersion compensation that is crucial to implement quantum networks in fiber.