High-fidelity transmission of polarization encoded qubits from an entangled source over 100 km of fiber

TL;DR

This paper demonstrates the transmission of polarization-entangled photon pairs over 100 km of fiber with high fidelity and visibility, enabling secure quantum communication.

Contribution

It presents a practical implementation of long-distance quantum communication using polarization-entangled photons at different wavelengths with minimal state degradation.

Findings

Raw visibility of 89% after 100 km fiber

State negativity decreases from 0.99 to 0.93 after transmission

Secure quantum cryptography is feasible over 100 km fiber

Abstract

We demonstrate non-degenerate down-conversion at 810 and 1550 nm for long-distance fiber based quantum communication using polarization entangled photon pairs. Measurements of the two-photon visibility, without dark count subtraction, have shown that the quantum correlations (raw visibility 89%) allow secure quantum cryptography after 100 km of non-zero dispersion shifted fiber using commercially available single photon detectors. In addition, quantum state tomography has revealed little degradation of state negativity, decreasing from 0.99 at the source to 0.93 after 100 km, indicating minimal loss in fidelity during the transmission.