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Optical Fiber Communication Conference

Nationwide Entanglement Distribution with Silicon Nanophotonic Chip

Jinyi Du, Xingjian Zhang, En Teng Lim, George F. R. Chen, Hongwei Gao, Dawn T. H. Tan, Alexander Ling

Published Jan 1, 2025• 0 citations
Publisher

Abstract

We developed a silicon chip capable of producing and delivering a detected rate of 460,000 pairs of entangled photons with a fidelity of 97.90(3)% fidelity. The entangled photons were transmitted over 155 km of fiber deployed across Singapore (66 dB loss), demonstrating a major advance in the capability of silicon nanophotonics for powering future quantum networks.

DOI
10.1364/ofc.2025.m4e.1

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We developed a silicon chip capable of producing and delivering a detected rate of 460,000 pairs of entangled photons with a fidelity of 97.90(3)% fidelity. The entangled photons were transmitted over 155 km of fiber deployed across Singapore (66 dB loss), demonstrating a major advance in the capability of silicon nanophotonics for powering future quantum networks.
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Entanglement distribution is critical for quantum networks, enabling secure communication and distributed quantum computing. We demonstrate long-distance polarization-entangled photon pair distribution using a silicon nanophotonic chip and ultra-low-loss (ULL) fiber. The polarization-entangled photons from the silicon chip achieve a fidelity of 97.90% with a raw observed entangled photon rate of 460,000 pairs/s. The chip is efficiently coupled to optical fiber with losses as low as 0.64dB per facet. Leveraging ULL fiber (0.16dB/km), we extend the entanglement distribution distance to over 300km, surpassing the previous record of 155km using deployed fiber. Key advancements include optimized splicing (sub-0.01dB loss) and active polarization correction, ensuring stable entanglement over long distances. This work highlights the potential of silicon photonics and ULL fiber for scalable and practical quantum communication networks.
Long-range quantum entanglement is essential for building large-scale quantum networks and unconditionally secure cryptographic systems based on quantum key distribution (QKD). While photonic integrated circuits offer a highly scalable platform, the fragility of phase coherence between spatial modes has prevented the distribution of path-encoded entanglement over long distances. Here, we report chip-to-chip distribution of path-encoded entangled states over 80 km between fully integrated silicon photonic transmitter and receiver chips. Telecom-band entangled photon pairs are generated via spontaneous four-wave mixing in on-chip spiral waveguides and distributed between chips over a dual-core, actively stabilized fiber link. Upon distribution, we measure a Bell state fidelity of 85.7±0.2%85.7 \pm 0.2 \%85.7±0.2%. Implementing the BBM92 protocol with the same source, we obtain a secure key rate of 2.03 bit/s in the infinite-key regime. These results establish silicon photonic chips as a viable platform for long-distance path-encoded entanglement-based quantum key distribution, paving the way toward scalable, device-independent quantum networks.
Transmitting entangled states over long distances is crucial for developing quantum networks. Previous demonstrations using satellites or fibers relied on photon pairs generated from bulk crystal arrangements. Polarization entanglement distribution based on complementary metal-oxide-semiconductor (CMOS)-compatible silicon chips has long been restricted to lab-scale demonstrations spanning only a few meters due to the difficulty of achieving sufficient off-chip brightness. Here, we report a silicon chip platform that provides an off-chip entangled photon pair brightness ranging from 8,000 to 460,000 pairs per second, exceeding previous reports by 3 orders of magnitude. The entanglement fidelity reaches 99.85(6)% and 97.90(3)%, respectively. After addressing key challenges in long-distance entanglement distribution over deployed fiber, including phase drift and chromatic dispersion, entangled photons were successfully distributed over 155 km (66 dB loss). These results demonstrate that CMOS-compatible silicon chips can perform competitively with bulk crystal sources and represent an important step toward scalable, chip-based quantum networks.
Advances in quantum photonics have shown that chip-scale quantum devices are translating from the realm of basic research to applied technologies. Recent developments in integrated photonic circuits and single photon detectors indicate that the bottleneck for fidelity in quantum photonic processes will ultimately lie with the photon sources. We present and demonstrate a silicon nanophotonic chip capable of emitting telecommunication band photon pairs that exhibit the highest raw degree of time-energy entanglement from a micro/nanoscale source, to date. Biphotons are generated through cavity-enhanced spontaneous four-wave mixing (SFWM) in a high-Q silicon microdisk resonator, wherein the nature of the triply resonant generation process leads to a dramatic Purcell enhancement, resulting in highly efficient pair creation rates as well as extreme suppression of the photon noise background. The combination of the excellent photon source and a new phase locking technique allow for the observation of a nearly perfect coincidence visibility of (96.6 ± 1.1)%, without any background subtraction, at a large pair generation rate of (4.40 ± 0.07) × 10 5 pairs/s.