A metropolitan quantum-network testbed uses fibre with attenuation
PHYSICS · Multi-part · Fermi University Physics · Quantum Information & Technology · Quantum states, measurement and entanglement · Quantum information theory and communication
Quantum Information and Technology, Ch Entanglement as a resource
Problem
A metropolitan quantum-network testbed uses fibre with attenuation 0.25dBkm−1. Estimate the probability that a photon is delivered:
((a)) over a single direct link of length 120km;
((b)) over two 60km half-links used for entanglement swapping, when both halves must herald a photon in the same attempt. Comment on whether swapping alone, without any further trick, improves on the direct link.