In a significant step toward scalable quantum networks, researchers are testing a high-precision optical timing technology known as White Rabbit to synchronize quantum devices. An experiment at CERN, the European Laboratory for Particle Physics, is successfully sending the White Rabbit timing signal through the same optical fiber as single photons from a source of quantum-entangled pairs. This achievement addresses a fundamental challenge in quantum communication: ensuring that distant network nodes operate on a perfectly synchronized clock, a requirement for manipulating the delicate states of quantum bits, or qubits.
The successful coexistence of the classical timing signal and the quantum signal within the same fiber optic cable could dramatically simplify the architecture of future quantum networks. These networks promise to connect quantum computers and sensors, enabling new frontiers in secure communication and distributed quantum computing. By leveraging the CERN-developed White Rabbit system, which offers sub-nanosecond accuracy, scientists are paving the way for robust, large-scale quantum systems that can maintain the fragile condition of entanglement over vast distances, a cornerstone of quantum information science.
The Quantum Synchronization Problem
Quantum networks derive their power from the unique properties of qubits, such as superposition and entanglement. Entanglement links the state of one qubit to another, regardless of the distance separating them, but harnessing this property requires exquisite coordination. For information to be processed or transmitted correctly, all nodes in the network must perform their operations within incredibly narrow time windows. If the timing is off by even a fraction of a second, the fragile quantum information can be lost, an effect known as decoherence.
Previous methods for synchronizing quantum networks often relied on GPS clocks or dedicated fiber optic lines solely for timing signals, which can be cumbersome and difficult to scale. Establishing a shared, common notion of time across a distributed network is a major engineering hurdle. Without a scalable and integrated solution, building complex, multi-node quantum networks capable of supporting a quantum internet or large-scale distributed quantum computing has remained a significant challenge. The goal is to create a timing system that is not only precise but also seamlessly integrated into the quantum channel itself.
Origins and Capabilities of White Rabbit
White Rabbit is an open-source technology initially developed at CERN to synchronize thousands of devices in the laboratory’s particle accelerators with extreme precision. It combines the accuracy of the worldwide industry standard Precision Time Protocol (PTP) with hardware-level enhancements to achieve sub-nanosecond accuracy and picoseconds precision in its synchronization. This level of performance is critical in accelerator environments where particle beams traveling near the speed of light must be controlled perfectly.
The technology works over standard Ethernet networks and optical fibers, allowing it to provide both timing and data communication simultaneously. This dual-use capability is what makes it a natural candidate for quantum networks, where minimizing infrastructure complexity and cost is paramount. In 2020, White Rabbit’s underlying technology was incorporated into the PTP standard by the Institute of Electrical and Electronics Engineers (IEEE), cementing its status as a robust and globally recognized solution for high-precision timing.
The CERN Quantum Initiative Experiment
At a specialized laboratory established by the CERN Quantum Technology Initiative (QTI), scientists are conducting a novel experiment to merge White Rabbit’s classical timing signal with a quantum signal. The goal is to transmit both signals concurrently through a single optical fiber without disrupting the quantum state of the photons. While other research teams have conducted similar tests, this is the first time the accelerator-born technology is being specifically tested for this purpose at CERN.
Experimental Setup and Partners
The current experiment combines the White Rabbit signal with photons from a source of entangled photon pairs. This quantum source hardware was supplied to CERN by the company Qunnect. To detect the faint quantum signals, the setup uses a superconducting nanowire single-photon detector provided by the firm Single Quantum. This collaborative setup allows researchers to precisely measure the performance and fidelity of the quantum channel while it shares the fiber with the powerful classical timing pulses from the White Rabbit system.
Improving on Previous Methods
Early results from related research have already demonstrated the superiority of this approach over older synchronization methods. One study highlighted a significant improvement in entanglement distribution fidelity when using White Rabbit components compared to systems synchronized with GPS clocks. The ultra-low timing jitter—a measure of deviation from true periodicity—provided by White Rabbit is a key factor in maintaining the integrity of the entangled photons as they travel through the network.
Broader Implications and Future Applications
The successful integration of White Rabbit technology into quantum networks has far-reaching implications. It could accelerate the development of a quantum internet capable of connecting quantum computers, sensors, and other devices across cities or even continents. Such networks would enable inherently secure communication through quantum cryptography, where the principles of quantum mechanics guarantee the privacy of the transmitted data. Any attempt to eavesdrop on the communication would disturb the quantum state and be instantly detected.
Beyond secure communications, these enhanced networks could be used to test fundamental concepts in physics, such as Bell inequalities and the very structure of spacetime. For distributed quantum computing, precise synchronization is essential for linking smaller, less powerful quantum processors together to create a single, more capable machine. This scale-out approach is seen as a crucial step toward building fault-tolerant quantum computers that can solve problems currently intractable for even the most powerful supercomputers.
Push for Standardization and Collaboration
Recognizing the broad potential of the technology, CERN has been instrumental in fostering a community around White Rabbit. In 2024, the laboratory launched the White Rabbit Collaboration, a global, membership-based community that brings together stakeholders from academia and industry to guide the technology’s future development and application. This effort aims to establish White Rabbit as a standard technology for quantum communication and other fields requiring high-precision timing.
The collaboration is already bearing fruit, with companies like Nu Quantum, a UK-based quantum entanglement startup, joining as the first quantum industrial partner. Nu Quantum is adopting White Rabbit to enable data-center-scale quantum computing networks and plans to release a Quantum Networking Unit that incorporates the technology. This partnership between a public research institution and private industry highlights the growing momentum behind creating the practical, real-world infrastructure needed to power the next generation of quantum technologies.