Chip-Integrated Broadband Multi-Photon Source for Wavelength-Multiplexed Quantum Networks

TL;DR

This paper demonstrates on-chip generation of broadband four-photon entanglement in the telecom band using lithium niobate waveguides, advancing scalable quantum networks with high fidelity and multiplexing capabilities.

Contribution

It introduces a broadband, integrated lithium niobate platform capable of generating multi-photon entanglement beyond photon pairs for quantum networks.

Findings

Achieved over 200 nm phase-matching bandwidth enabling multi-photon entanglement.

Measured two-photon entanglement fidelity of 0.874 with high brightness.

Demonstrated four-photon entanglement with improved rate and fidelity over previous platforms.

Abstract

Quantum networks based on wavelength-multiplexed entanglement enable parallel distribution of quantum correlations, increasing channel capacity for secure communication and distributed quantum information processing. However, broadband integrated sources capable of generating multipartite entanglement beyond photon pairs remain scarce. Here we report on-chip generation of telecom-band four-photon entanglement in a periodically poled thin-film lithium niobate on insulator (LNOI) waveguide. Type-0 spontaneous parametric down-conversion provides a phase-matching bandwidth exceeding 200 nm, enabling spectrally separable generation of multi-photon entanglement across the telecom band. The generated photons are encoded in time bins for robust fiber compatibility, and a coherent interface enabling reversible conversion between time-bin and polarization degrees of freedom allows complete quantum state tomography. We measure two-photon entanglement with a brightness of 6.7 MHz/mW/nm and a fidelity of $0.874 \pm 0.002$. At a pump power of 0.08 mW, the four-photon state exhibits a fourfold coincidence rate of 1 Hz and a fidelity of $0.74 \pm 0.01$, representing a threefold improvement over previous integrated platforms. Our results establish LNOI as a scalable platform for broadband multi-photon entanglement and provide a practical route toward dense wavelength-multiplexed quantum networks.