Synchronized distribution of quantum entanglement coexisting with high-rate, broadband classical optical communications over a real-world fiber link
Gina M. Talcott, Ahnnika I. Hess, Laura d'Avossa, Scott J. Kohlert, Fei I. Yeh, Jim Hao Chen, Joe J. Mambretti, Tim M. Rambo, Gregory S. Kanter, Jordan M. Thomas, Prem Kumar
quant-phSubmitted Jan 30, 2026• Announced Feb 3, 2026• 4 citations
Compatibility with existing classical network infrastructure offers a scalable path towards deploying largescale quantum networks. Here, we demonstrate O-band polarization-encoded quantum entanglement distribution over an installed 24.4-km fiber while coexisting with a state-of-the-art fully-loaded C-band classical communications line system and a picosecond-level precision L-band synchronization signal. The classical system carries two 800-Gbps channels while the remainder of the C-band is filled with amplified spontaneous emission as is standard for such state-of-the-art communications systems. We examine the spontaneous Raman scattering spectrum generated from this broadband C-band light and offer insights into wavelength allocation for O-band quantum channels. Optimal wavelength selection and narrow filtering enable well-preserved Bell state fidelity when coexisting with 21.4-dBm aggregate launch power across the C-band suitable for 36 Tbps transmission. To the best of our knowledge, this is the first implementation of entanglement-based quantum communications between two remote nodes coexisting with independent classical communications traffic. We demonstrate coexistence of quantum entanglement with ultra-high power levels and record classical bandwidth, offering promise for real-world entanglement-based networking integrated within high-capacity communications infrastructure.
Compatibility with existing classical network infrastructure offers a scalable path towards deploying largescale quantum networks. Here, we demonstrate O-band polarization-encoded quantum entanglement distribution over an installed 24.4-km fiber while coexisting with a state-of-the-art fully-loaded C-band classical communications line system and a picosecond-level precision L-band synchronization signal. The classical system carries two 800-Gbps channels while the remainder of the C-band is filled with amplified spontaneous emission as is standard for such state-of-the-art communications systems. We examine the spontaneous Raman scattering spectrum generated from this broadband C-band light and offer insights into wavelength allocation for O-band quantum channels. Optimal wavelength selection and narrow filtering enable well-preserved Bell state fidelity when coexisting with 21.4-dBm aggregate launch power across the C-band suitable for 36 Tbps transmission. To the best of our knowledge, this is the first implementation of entanglement-based quantum communications between two remote nodes coexisting with independent classical communications traffic. We demonstrate coexistence of quantum entanglement with ultra-high power levels and record classical bandwidth, offering promise for real-world entanglement-based networking integrated within high-capacity communications infrastructure.
The ability for quantum and conventional networks to operate in the same optical fibers would aid the deployment of quantum network technology on a large scale. Quantum teleportation is a fundamental operation in quantum networking, but has yet to be demonstrated in fibers populated with high-power conventional optical signals. Here we report, to the best of our knowledge, the first demonstration of quantum teleportation over fibers carrying conventional telecommunications traffic. Quantum state transfer is achieved over a 30.2-km fiber carrying 400-Gbps C-band classical traffic with a Bell state measurement performed at the fiber’s midpoint. To protect quantum fidelity from spontaneous Raman scattering noise, we use optimal O-band quantum channels, narrow spectro-temporal filtering, and multi-photon coincidence detection. Fidelity is shown to be well maintained with an elevated C-band launch power of 18.7 dBm for the single-channel 400-Gbps signal, which we project could support multiple classical channels totaling many terabits/s aggregate data rates. These results show the feasibility of advanced quantum and classical network applications operating within a unified fiber infrastructure.
Entanglement distribution between spatially distant nodes is crucial for advancing the development of quantum networks. Achieving large-scale, practical quantum networks by leveraging existing fiber infrastructures and commercial technologies can greatly enhance cost efficiency in real-world applications. As such, the simultaneous transmission of quantum entanglement and classical signals within a single optical fiber is becoming increasingly desirable, yet it remains challenging due to the substantial intensity disparities between single-photon-level quantum light and classical traffic. In this study, we theoretically describe and experimentally implement polarization entanglement distribution using a continuous wave pumped integrated AlGaAs Bragg reflection waveguide quantum source, coexisting with classical light in optical fiber at the telecom C-band. The characteristics of noise photons are analyzed and evaluated under different levels of classical light power. Using the BBM92 protocol for quantum key distribution, we demonstrate that temporal and spectral filtering during coincidence detection, combined with optimized source brightness, effectively influences the secure key rate and achievable distance of the system. Polarization drift is measured across various fiber paths, with 35-hour stability tests on fibers ranging up to 55 km in length. Our results can guide the initial design of optimal entanglement distribution networks that are compatible with fiber-optic communication systems.
The scalability of quantum networking will benefit from quantum and classical communications coexisting in shared fibers, the main challenge being spontaneous Raman scattering noise. We investigate the coexistence of multi-channel O-band quantum and C-band classical communications. We characterize multiple narrowband entangled photon pair channels across 1282 nm-1318 nm co-propagating over 48 km of installed standard fiber with record C-band power (>18 dBm) and demonstrate that some quantum-classical wavelength combinations significantly outperform others. We analyze the Raman noise spectrum, optimal wavelength engineering, multi-photon pair emission in entangled photon-classical coexistence, and evaluate the implications for future quantum applications.
We present polarization entanglement distribution over an operator-owned, metropolitan-scale fiber network, employing standard wavelength-division multiplexing components to achieve coexistence of O-band photons and C-band classical light. First, we demonstrate dynamic path switching by alternating between 15-km and 30-km deployed fiber loops, enabled by automated polarization compensation achieving sub-second recovery and time-averaged CHSH S -values exceeding 2.65 over 21 hours. We then assess the impact of co-propagating 100-Gbit/s C-band classical signals by varying launch powers up to 6 dBm. Finally, by combining path switching and classical co-propagation, we achieve stable entanglement distribution over 30 km of deployed fiber, validating the feasibility of hybrid quantum–classical transmission and paving the way for entanglement-based quantum networking on existing metropolitan infrastructure.
Integrating quantum key distribution (QKD) with classical optical communication is a deployment-friendly and cost-effective approach to advancing QKD network implementation. However, the noise introduced by intense classical signals into the quantum channel severely impacts the performance of the QKD system, presenting challenges for long-distance coexistence transmission. In this paper, we successfully demonstrate the simultaneous propagation of QKD and optical transport network (OTN) in the C-band over distances exceeding 100 km. We establish a coexistence transmission system based on a commercial OTN equipment and QKD device equipped with the Fabry-Perot filters, demonstrating the feasibility of combining QKD with 11 Tbps (110×100 Gbps) classical data over a 101.86 km fiber. To investigate longer transmission distances, we employ an optimized wavelength allocation method and conduct the co-propagation of QKD and 1 Tbps classical data over a 152.34 km fiber. To the best of our knowledge, these results are the first time that report the integration of QKD and large-capacity classical communication over hundred-kilometer scale fiber. Our works represent a significant advancement in developing OTN networks incorporating QKD systems.
The coexistence of quantum and classical signals in the same optical fiber is a critical challenge for the deployment of quantum networks. Indeed, selecting an optimal channel for quantum signal transmission is crucial to minimize noise arising from co-propagating classical signals. This work experimentally investigates spontaneous Raman scattering (SpRS), a major source of noise in signals transmitted along the same fiber. Unlike most previous studies relying on narrow-linewidth laboratory lasers or architectures based on spatial or temporal multiplexing of quantum and classical signals, we employ commercial SFP optical transceivers and standard single-core single-mode fiber for the transmission of quantum and classical signals in the same fiber, reflecting conditions typical of deployed urban fiber infrastructures. Building on these measurements, we derive a compact and predictive model that captures the Raman scattering profile, enabling accurate estimation of SpRS noise as a function of source power, wavelength, and fiber length. A key outcome of this work is that the proposed model is independent of the specific optical source used, demonstrating its generality and robustness. The model can therefore be used for the identification of optimal C-band channels for quantum signal allocation, namely those least affected by SpRS noise generated by co-propagating O-band classical traffic. These results pave the way for a parameter-robust description of Raman scattering applicable to diverse fiber-based systems.