A small, innovative experiment at CERN is paving the way for new techniques in quantum networks and quantum cryptography.
The goal of the experiment is to test how the CERN-born optical timing signal – normally used in the Laboratory’s accelerators to synchronise devices with ultra-high precision – can best be sent through an optical fibre alongside a single-photon signal from a source of quantum-entangled photons.
Scientists have recently set up a specialised laboratory to test how the CERN-born White Rabbit optical timing signal can be transmitted most effectively, along with entangled photons, through an optical fibre.
While similar experiments have been done previously by other research teams worldwide, this is the first time this technology, originally developed to synchronise accelerator devices, is being tested locally at CERN for this purpose.
A growth of interest in quantum networks
Research in quantum networks is growing rapidly worldwide.
Future quantum networks could connect quantum computers and sensors, preserving all quantum information. They could also facilitate the secure exchange of information, enabling applications across various fields.
Unlike classical networks, where information is encoded in binary bits (0s and 1s), quantum networks rely on the unique properties of quantum bits, or “qubits,” such as superposition (where a qubit can exist in multiple states simultaneously) and entanglement (where the state of one qubit influences the state of another no matter how far apart they are).
These properties allow quantum networks to perform tasks that are impossible or inefficient for classical networks. They can even be used to test fundamental physics concepts such as Bell inequalities and the structure of spacetime.
What makes the White Rabbit technology unique?
“The White Rabbit timing technology is the natural candidate for application in quantum communication as it provides sub-nanosecond accuracy and picoseconds precision in synchronisation, making it suitable for large distributed systems and quantum networks,” explained Annick Teepe, the scientist in charge of the CERN quantum network lab.
The same timing precision is required in quantum key distribution, a protocol that generates secure encryption keys for quantum cryptography.
“High timing precision is critical for demonstrating the distribution of entangled photon pairs, which forms the basis of entanglement-based quantum key distribution,” Annick stated.
“Unlike other existing time synchronisation technologies, White Rabbit is open source and based on standards.”
Synchronising the quantum networks of the future
In the current experiment, the White Rabbit classical timing signal is combined with a quantum signal from a source of entangled photon pairs that was supplied in-kind to CERN by Qunnect.
The setup also utilises a superconducting nanowire single-photon detector, which was provided in-kind by Single Quantum.
Amanda Díez Fernández, coordinator of partnerships for QTI, concluded: “With our tests, we aim to contribute to the global effort around the synchronisation of quantum networks and to help establish White Rabbit as a standard technology for quantum communication, even in distributed and complex settings.”
