Short answer: Silicon photonic chips can generate entangled photon pairs for quantum communication in a compact, integrated form. Published experiments report a telecom-band chip with built-in pump filtering, a chip source that links visible and telecom wavelengths, and a hyper-entangled source exceeding 10^9 pairs per second. These are laboratory sources, and the figures are the authors' own.
What the chips are for
A 2020 npj Quantum Information paper says that combining quantum and integrated photonics promises to produce, manipulate and detect quantum states of light with compact, scalable systems. Photon pair sources are fundamental building blocks for quantum entanglement and communication, as a 2018 Nature Physics paper puts it, and silicon photonics has shown promising characteristics in the telecom band, including sub-milliwatt optical pump power, high spectral brightness and high photon purity.
Filtering the pump on the chip, 2020
The 2020 paper notes that putting everything needed for high-quality telecom-band entanglement on one chip has been hard, mainly because of the limited performance of on-chip filters that reject the pump light. The authors report a stand-alone, telecom-compliant device that integrates a nonlinear photon-pair generator and a passive pump-rejection filter on one substrate. Using standard channel-grid fibre demultiplexers, they report the first entanglement qualification of such an integrated circuit, with the highest raw quantum interference visibility for time-energy entangled photons over two telecom bands, and say pure, maximally entangled states can be generated.
Bridging visible and telecom wavelengths, 2018
The 2018 paper points out that most quantum systems suited to local operations such as storage and computation have optical transitions in the visible or short near-infrared, where silica fibre loses more light than at telecom wavelengths. This limits the distance over which fibre-based communication between such nodes can run. The paper describes a chip-integrated photon pair source with one photon in the visible and one in the telecom band, as one approach to connecting those systems over fibre.
A high-rate hyper-entangled source, 2025
A 2025 npj Nanophotonics paper addresses optical loss and environmental noise over long distances. One strategy is to raise the emission rate as far as possible, and another is hyper-entanglement, meaning entanglement over several degrees of freedom, to resist decoherence. The authors demonstrate a silicon-integrated device that does both, emitting spectrally multiplexed, hyper-entangled photon pairs at a rate exceeding 10^9 pairs per second.
Limits
The papers measure source quality in the laboratory, using their own metrics such as interference visibility and pair rate. They do not report a deployed link, and the designs differ, so the numbers are not a ranking.
How to compare them
The three sources aim at different problems. The 2020 device is about purity and filtering in one telecom-compatible chip. The 2018 device is about matching the wavelengths of local quantum systems to those of long-distance fibre. The 2025 device is about brightness and robustness through hyper-entanglement. A reader should look at which problem each paper reports solving, and treat the metrics, such as visibility, pair rate and purity, as specific to that design and measurement.
FAQ
What is a photon pair source?
A device that emits photons in entangled pairs, used as a building block for quantum communication.
Why integrate the pump filter on the chip?
Rejecting the pump light is needed for pure entangled states, and on-chip filters have limited performance.
What is hyper-entanglement?
Entanglement across more than one degree of freedom of the photons.
How fast was the fastest source?
The 2025 paper reports more than 10^9 pairs per second.
Is this in use in networks today?
These papers report laboratory sources only.
All field notes