A single microchip-sized laser will soon transmit both ultra-precise clock signals and quantum-encrypted data down the same optical fibre, without the two interfering. Today’s quantum networks require separate, bulky hardware for timing and for quantum key distribution, making them impractical for real-world telecoms. This project tackles that bottleneck by engineering a “microcomb”—a tiny optical cavity that generates many equally spaced laser frequencies at once. The team exploits a topological effect, akin to a Möbius strip, to keep classical timing signals and fragile quantum states in separate but coexisting channels within the same device. If successful, the work directly supports three UK quantum missions: secure communications (Mission 2), ultra-precise positioning and navigation (Mission 4), and network synchronisation (Mission 5). A practical microcomb source would allow telecom operators to distribute quantum keys and atomic-clock-grade timing across existing fibre networks without adding hardware. That could make financial transactions, power-grid coordination, and 5G base-station synchronisation both faster and fundamentally unhackable. The project is largely fundamental—it must first validate that topological protection works for quantum states in a nonlinear cavity. But the payoff is a compact, integrated source that bridges classical and quantum infrastructure, a step that has eluded the field for years.
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The project investigates the use of nonlinear parametric generation in micro-resonators, for future networks, focusing on the integration of classical and quantum channels within a single, compact microcomb source. Such a source will enable the distribution of both an ultraprecise clock signal for ultradense optical communication and quantum-secure information. Microcombs are optical sources that produce equally spaced frequencies using compact microcavities, with key impacts in metrology and quantum optics. Our approach explores novel topologically protected regimes arising from the interplay between topology and nonlinearity sustained by cavity solitons—microcomb states characterised by high spectral efficiency and resilience to perturbations. These features make them particularly suited for applications requiring robust and precise control, such as metrology, and we envision their application in quantum optics. Quantum communication is a priority within the National Quantum Technology Programme for both Canada and the UK (QT Mission 2). Hence, the development of practical quantum sources compatible with classical networks is a key technology in these areas. Moreover, the project envisions a system capable of transmitting ultraprecise clock signals, directly targeting UK QT Mission 4 on position, navigation, and timing, and network synchronisation under UK QT Mission 5. The primary objectives are: to validate the topological protection of quantum states, to generate combined classical and quantum microcombs, to lock classical microcomb states to atomic references, and to validate the persistence of quantum microcomb channels when the classical comb is locked to the metrological reference. To meet these goals, our research leverages a nested-cavity microcomb laser to achieve simultaneous generation of a primary comb for synchronisation with atomic references and quantum-correlated photons in different channels of the same nonlinear microcavity. The topological protection inherent in this design isolates the classical and quantum combs in distinct resonator modes, overcoming challenges related to crosstalk and ensuring the stability of quantum channels in the presence of classical signals. Moreover, the quantum states are pumped directly by the classical state oscillating in the microcomb. Such a source enables new kinds of classical-quantum sources and has important potential for future telecommunications, requiring ultrafast data synchronisation and quantum-secure protocols within the same networks. To realise the topological approach, a main oscillating microcomb in the microcavity sustains secondary states with a phase shift in one loop significantly different from 0 (i.e., a large fraction of p). These states exist due to a field transformation in the cavity (a topology), allowing the optical path to close in more than one cavity round-trip. In the literature, this has been realised in so-called Möbius topologies, where these modes oscillate in equivalent 'cavities' that exist and are protected by the system's nonlinearity. Key to exploiting this regime is a setting in which those modes are below the oscillation threshold and are kept fed only by spontaneous conversion of the comb lines. Our investigation, combining theoretical and experimental approaches, will characterise the stability, efficiency, coherence, and correlation properties of these microcombs, assessing their potential for integration into existing networking infrastructures. This project leverages the joint expertise of Canadian and UK researchers in quantum and lasing microcombs, providing a strong foundation of established knowledge and research infrastructure. The outcomes will significantly advance the development of quantum technologies and their application in the next generation of communication networks.
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