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Enabling Precision for Quantum Applications Country Wide and broader: Planning Optical Time Dissemination via White Rabbit on Shared Research Fiber Backbone

Josef Vojtěch, Ondřej Havliš, Tomáš Novák, Jaromír Šíma, Vladimír Smotlacha, Michal Hažlinský, Raimena Veisllari, Guy Roberts, Elisabeth Andriantsarazo, Michal Spacek, Martin Šlapák, Lada Altmannová, Rudolf Vohnout, Radek Velc, Petr Pospisil, Martin Čížek, Jan Hrabina, Šimon Řeřucha, Lenka Pravdová, Ondřej Čı́p, Pavel Peterka, Jaroslav Roztočil

Published Jan 1, 2026• 0 citations
Publisher

Abstract

We present implementation of precise time dissemination using the White Rabbit protocol over shared optical fibers within research backbones. It highlights advancements in synchronization accuracy, shared infrastructure efficiency, and implications for scientific and possible industrial applications.
DOI
10.1364/cleo_at.2026.ath2a.4

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White Rabbit (WR) technology provides a commercially-available off-the-shelf solution for time synchronisation with sub-nanosecond accuracy and picosecond-level precision over optical fibre links typically spanning tens of kilometres. Such high-performance time dissemination can support a variety of applications, including position, navigation and timing (PNT), financial transactions, metrology, as well as entanglement and quantum key distribution (QKD). Demonstrations of WR over significantly longer distances remain few and far between, particularly in scenarios where intermediate amplification is unavailable, such as stretches of long-haul underwater fibre. In this work, we report the longest unrepeated deployment of WR to date, achieving time synchronisation over a 300 km (51.34 dB) single-span optical fibre link, even in highly asymmetrical configurations, with 99.86% uptime, whilst maintaining picosecond-level precision and sub-nanosecond accuracy. This was achieved through careful selection and optimisation of the components deployed at the link's end points. By leveraging standard telecom fibre and off-the-shelf hardware, our results pave the way for a scalable and standardised timing backbone for large-scale quantum networks, offering a practical route toward time distribution in future heterogeneous quantum communication systems.
With the increasing demand for ultra-precise time synchronization and frequency dissemination across various scientific, industrial, and communication fields, the Czech Republic has developed an innovative, non-commercial fiber-based infrastructure. This infrastructure serves as a shared platform, utilizing optical fibers to enable high-precision timing, coherent frequency transfer, and a newly implemented vibrational sensing capability. The project also addresses challenges posed by classical communication noise—particularly from Raman scattering—on quantum channels, especially for Quantum Key Distribution (QKD). By strategically separating classical and quantum channels into distinct wavelength bands, such as the C-band and O-band, the infrastructure achieves minimal interference while enabling multiple concurrent applications over shared fiber lines.
Precise timing synchronization is essential for distributed quantum networking, enabling entanglement distribution, quantum teleportation, and entanglement swapping across remote nodes. Existing synchronization architectures rely on dedicated timing-distribution infrastructure, most notably White Rabbit networks, which constrain topology, scalability, and deployment in free-space and satellite environments. Here we demonstrate link-free synchronization of quantum network nodes using independently operating miniature rubidium atomic clocks and computational post-processing. We validate the approach on a deployed metropolitan-scale telecom fiber network spanning three geographically separated nodes. Following drift correction, atomic-clock-based synchronization achieves timing performance approaching that of a White Rabbit benchmark and remains stable over continuous 8-hour operation. As a stringent test of quantum-network functionality, we observe Hong-Ou-Mandel interference across spatially separated nodes with visibility exceeding 70%, statistically equivalent to that obtained using dedicated White Rabbit timing links. To the best of our knowledge, this represents the first observation of quantum interference across a deployed metropolitan-scale telecom fiber network synchronized entirely without dedicated timing-transfer infrastructure. These results establish atomic-clock-based synchronization as a scalable, topology-independent alternative to conventional timing-distribution architectures and a practical pathway toward terrestrial, airborne, and space-based quantum networks where dedicated timing links are unavailable.
In the ever-advancing realm of modern technology, the demand for unparalleled precision and stability in timekeeping and frequency control has surged to unprecedented heights. As our interconnected world rellies more than ever on intricate synchronization and seamless communication, the development of cutting-edge optical infrastructure has emerged as a cornerstone in meeting these exacting demands. There has been obvious increased continuous focus on precise time and frequency transmission dissemination at a national and international level recently. We would like to present the situation in the Czech Republic, our strategy, approach, and our experience with a non-commercial, costeffective solution that utilizes optical networks shared with other traffic. The presented solution provides accurate time and stable frequency at a lower operational cost, using the shared spectrum of the CESNET3 network infrastructure.
Quantum networks leverage the laws of quantum mechanics to transport quantum states over geographic distances by using the quantum teleportation and entanglement swapping protocols. These protocols necessitate successful Bell state measurements which require the distribution of high precision timing between the participating nodes. White Rabbit (WR) is a precision timing protocol developed at the European Organization for Nuclear Research (CERN) which provides the means to obtain sub-nanosecond time resolution between nodes in a terrestrial quantum optical network using optical Ethernet switches. The purpose of this research is to characterize the error in distributed high precision timing when using the White Rabbit protocol wave division multiplexed in single-mode optical fiber as a function of time of day, length of fiber, percentage of aerial fiber, and environmental conditions (e.g., temperature, humidity, barometric pressure, wind speed, cloud cover). We evaluate and compare several statistical machine learning models in terms of their ability to accurately predict distributed timing error as a function of several geographic and environmental variables. The long-term goal of this research effort is to support decision making when implementing a quantum network using existing low-cost conventional optical telecommunications infrastructure technologies.