In a stride toward the realization of functional quantum networks, a team of researchers from the National Institute of Standards & Technology (NIST) and the University of Colorado, Boulder, has demonstrated the successful transmission of single photons conveying quantum information across kilometers of noisy fiber optic cables. Significantly, the photons retain their quantum coherence and fidelity despite traveling through real-world, environmentally perturbed fiber, marking a critical milestone in scalable quantum communication infrastructure.
Quantum networks promise to revolutionize several burgeoning technological fields, including distributed quantum computing and quantum sensor networks, by leveraging the unique properties of quantum mechanics. The entanglement and superposition of quantum states allow these networks to enable secure communications and cooperative quantum processing across disparate nodes. However, a formidable challenge in this domain rests in preserving fragile quantum states during transmission through fiber, which is susceptible to environmental noise and physical disturbances.
The innovative approach pioneered by the researchers draws on advanced fiber stabilization techniques originally developed for the synchronization of optical atomic clocks. These methods provide optical path length stabilization with astonishing nanometer-scale precision, enabling the mitigation of fiber-induced fluctuations. Here, the team adapts these techniques to quantum network protocols by simultaneously stabilizing the fiber’s optical path and detecting single photons that carry the quantum data, a complex feat due to the stark contrast in intensity between the bright stabilization reference light and the single-photon quantum signals.
A key technical hurdle in such systems is the “co-existence challenge,” referring to the difficulty of separating the overpowering classical stabilization light from the extremely faint quantum signal photons within the same fiber channel. The researchers overcome this by employing a clever temporal multiplexing strategy: the reference laser for fiber stabilization pulses briefly to sense and correct fiber distortions, then ceases operation to allow quantum photons to pass through an effectively noise-free medium. This synchronized cycling, operating thousands of times per second, ensures real-time noise correction without contaminating the quantum channel.
Beyond stabilizing the optical fiber, precise timing control is imperative for maintaining quantum coherence. Minor temporal jitter can destroy the delicate phase relationships between photons, causing irreparable quantum state degradation. The team details their success in reducing timing jitter induced by the fiber to less than 100 attoseconds — an interval astoundingly small on the scale of a billionth of a billionth of a second — thereby safeguarding phase information essential for quantum interference measurements.
To rigorously validate their approach, experiments were conducted using two independent 2-kilometer fiber links subjected to conditions more turbulent than typical underground installations. The quantum photons emerging from both fibers exhibited indistinguishability greater than 99%, signaling that the quantum states were preserved with minimal decoherence. Such indistinguishability is critical for advanced quantum networking protocols, including entanglement swapping and quantum teleportation.
Another pillar of system integrity concerns the potential leakage of classical stabilization photons into the quantum channel, which could undermine quantum measurements by introducing noise. The researchers demonstrate an isolation ratio exceeding 80 billion to one, ensuring that for every ten million quantum photons detected, fewer than one classical photon infiltrates the quantum channel, thus maintaining the purity of quantum state detection.
This milestone achievement lays the groundwork for deploying quantum repeaters — devices essential for extending quantum communication beyond metropolitan scales where signal loss and decoherence pose severe limits. The research team is now working to integrate this stabilized fiber infrastructure with reliable, identical single-photon sources and advanced single-photon detectors to realize fully functional quantum repeaters capable of supporting long-distance quantum information transmission.
Looking ahead, the researchers envision scaling the stabilized fiber network to encompass numerous spatially distributed nodes, thereby enabling complex quantum protocols that extend beyond simple communication to distributed quantum computation and sensing. Such networks would permit quantum information to be shared and processed among many physically separated quantum processors, opening new horizons in quantum technology.
This work represents a confluence of disciplines, combining expertise in quantum optics, optical frequency metrology, and photonics engineering. Drawing on decades of progress in optical atomic clocks with 18-digit precision frequency comparisons, the team successfully translates these high-precision stabilization methods from the domain of timekeeping to the realm of photonic quantum networks.
As quantum networks edge closer to practical applications, this research demonstrates a crucial capability: transmitting quantum information over noisy, real-world fibers without sacrificing coherence or fidelity. Such advances are indispensable for moving beyond laboratory demonstrations toward operational quantum communication systems robust to the unpredictability of existing fiber infrastructure.
The study, published in the Optica Publishing Group journal Optica Quantum, is authored by N. V. Nardelli and colleagues and represents a landmark contribution to quantum network protocols. By taming the formidable challenges of stabilizing optical fibers in the presence of noise while preserving single-photon quantum signals, this work significantly propels the field forward, heralding a new era of quantum connectivity.
Subject of Research: Quantum state preservation during single-photon transmission in noisy optical fiber links for quantum networking applications.
Article Title: Phase-Stable Optical Fiber Links for Quantum Network Protocols
Web References:
– https://opg.optica.org/opticaq/viewmedia.cfm?uri=opticaq-4-2-138&html=true
– https://www.nist.gov/
– https://www.colorado.edu/
– https://opg.optica.org/opticaq/home.cfm
References:
N. V. Nardelli, D. V. Reddy, M. Grayson, D. Sorensen, M. J. Stevens, M. D. Mazurek, L. K. Shalm, T. M. Fortier, “Phase-Stable Optical Fiber Links for Quantum Network Protocols,” Optica Quantum, vol. 3, pp. 138-147, 2026. DOI: 10.1364/OPTICAQ.571592
Image Credits: Nick Nardelli, National Institute of Standards & Technology (NIST)
Keywords:
Quantum optics, Fiber optics, Quantum networks, Optical fiber stabilization, Quantum communication, Single-photon transmission, Phase stabilization, Quantum interference, Optical atomic clocks, Quantum state fidelity, Quantum repeaters, High-precision metrology
