High-fidelity entanglement swapping and generation of three-qubit GHZ state using asynchronous telecom photon pair sources

TL;DR

This paper demonstrates high-fidelity entanglement swapping and GHZ state generation using asynchronous telecom photon sources, employing time-resolved detection to achieve indistinguishability without active synchronization.

Contribution

It introduces a method for entanglement swapping and GHZ state creation with asynchronous sources using time-resolved detection, eliminating the need for active timing synchronization.

Findings

Fidelities of 0.84 for entanglement swapping and 0.70 for GHZ state generation.

Use of fiber-based Bragg gratings and superconducting nanowire detectors for high-quality photon detection.

Successful demonstration of asynchronous photon source compatibility with quantum communication protocols.

Abstract

We experimentally demonstrate a high-fidelity entanglement swapping and a generation of the Greenberger-Horne-Zeilinger~(GHZ) state using polarization-entangled photon pairs at telecommunication wavelength produced by spontaneous parametric down conversion with continuous-wave pump light. While spatially separated sources asynchronously emit photon pairs, the time-resolved photon detection guarantees the temporal indistinguishability of photons without active timing synchronizations of pump lasers and/or adjustment of optical paths. In the experiment, photons are sufficiently narrowed by fiber-based Bragg gratings with the central wavelengths of 1541~nm and 1580~nm, and detected by superconducting nanowire single-photon detectors with low timing jitters. Observed fidelities are 0.84 \pm 0.04 and 0.70 \pm 0.05 for the entanglement swapping and generation of the GHZ state, respectively.