Quantum states prepared by realistic entanglement swapping

TL;DR

This paper provides a detailed theoretical analysis of the quantum states produced by realistic entanglement swapping, accounting for experimental imperfections, and compares predictions with experimental data.

Contribution

It introduces a closed-form solution for the states generated by entanglement swapping considering real-world inefficiencies and imperfections.

Findings

Realistic imperfections significantly affect entanglement quality.

Theoretical predictions align well with experimental results.

Implications for quantum communication protocols.

Abstract

Entanglement swapping between photon pairs is a fundamental building block in schemes using quantum relays or quantum repeaters to overcome the range limits of long-distance quantum key distribution. We develop a closed-form solution for the actual quantum states prepared by realistic entanglement swapping, which takes into account experimental deficiencies due to inefficient detectors, detector dark counts, and multiphoton-pair contributions of parametric down-conversion sources. We investigate how the entanglement present in the final state of the remaining modes is affected by the real-world imperfections. To test the predictions of our theory, comparison with previously published experimental entanglement swapping is provided.