Feasibility of UK-Ireland Underwater Quantum Communications
In an important step towards practical quantum networks over existing telecommunications infrastructure, a research team has successfully demonstrated the feasibility of a 224-km undersea cable for quantum communications. The cable, owned and operated by bandwidth infrastructure provider euNetworks, runs between Ireland and the UK under the Irish Sea.
The researchers performed a series of experiments to assess the suitability of this fiber link for quantum communications protocols. First, they measured the relative phase drift between two paired fibers in the channel, finding phase variations within the range of common stabilization techniques. This suggests the channel could allow successful implementation of phase-based protocols such as twin-field quantum key distribution (QKD). Next, they studied the polarization stability of the channel, implementing a proof-of-concept, prepare-and-measure-based QKD protocol to explore the timescales over which polarization is sufficiently stable. The results are promising for implementation of a polarization-encoded BB84 protocol. Finally, they demonstrate the presence of entangled photon pairs via coincidence measurements, after these photons have each traveled 224 km over their separate fibers, and in the presence of significant channel noise.
All of these results required high-efficiency, low-noise detectors, and ID Quantique (IDQ) are proud that their ID281 Superconducting Nanowire detectors were used in this work. The detectors used had system detection efficiencies of 93.0% and 90.5% at 1550 nm, as well as dark count rates of less than 70 cps.
This demonstration represents a major milestone towards building international quantum communication networks over existing infrastructure. The success of these feasibility tests with deployed submarine fiber highlights progress in integrating quantum protocols with real-world telecom systems. With continued advancements in reducing noise, long-haul quantum communication may soon emerge from the lab.
Companies like ID Quantique play a key role in this effort by supplying the sensitive detector solutions needed to transmit quantum states across today’s fiber networks, pushing the boundaries of what is possible. To request more information or a quotation for any ID Quantique products, contact IL Photonics.