Fibre Optic Upgrades Cut Quantum Hardware Needs by 49 Percent

Giovanni Simone Sticca and colleagues at Politecnico di Milano show that selective implementation of hollow-core fibres enables efficient coexistence between different technologies. Their findings reveal that upgrading just 40% of links within a metropolitan network topology can decrease the required number of quantum modules by as much as 49%, representing a key step towards cost-effective and scalable quantum communication infrastructure.

Hollow-core fibre deployment substantially lowers quantum network infrastructure expenses

Upgrading 40 per cent of links with hollow-core fibre reduces the number of quantum modules required in a metropolitan network by up to 49 per cent compared to networks utilising only standard single-mode fibre. This sharp reduction overcomes a previous barrier to widespread quantum key distribution (QKD) deployment, as historically the high cost of dedicated infrastructure hindered scalability. Hollow-core fibre, a relatively new optical technology allowing light to travel through air instead of glass, minimises signal loss and interference which previously limited quantum signal transmission distances. Standard single-mode fibres rely on total internal reflection to guide light, inherently causing some signal attenuation due to material absorption and scattering. Hollow-core fibres, however, leverage a different principle, photonic bandgap guidance or anti-resonant reflection, to confine light within the air-filled core, dramatically reducing these losses, particularly at wavelengths crucial for quantum communication.

A key benefit is the ability to extend transmission ranges and improve signal integrity for secure communication. Quantum key distribution (QKD) network costs are significantly affected by deploying hollow-core fibre alongside standard single-mode fibre. Guiding light through air instead of glass allows hollow-core fibre to operate in the C-band, a frequency range often disrupted by noise from classical signals in standard fibre. This differs from conventional systems, which limit quantum transmissions to the O-band to avoid interference. The O-band covers approximately 1260–1360 nanometres (232-236THz), while the C-band covers approximately 1530–1565 nanometres (192-196THz). The C-band is heavily utilised for dense wavelength division multiplexing (DWDM) in classical communications, creating a noisy environment for sensitive quantum signals. Hollow-core fibre’s reduced sensitivity to these classical signals allows for simultaneous operation without significant degradation of the quantum channel. Simulations on a metropolitan network topology revealed that reduced Raman scattering within hollow-core fibre enables longer transmission distances and higher secret key rates, crucial for secure communication. Raman scattering, a non-linear optical process, causes photons to shift in wavelength, introducing noise and limiting transmission distance. Hollow-core fibres exhibit significantly lower Raman scattering coefficients compared to standard silica fibres. The modelling incorporates fibre attenuation, spontaneous Raman scattering, and four-wave mixing to calculate achievable key rates, assuming a 1dB insertion loss at each network node. A 40 per cent upgrade to hollow-core fibre in a metro topology can reduce the number of quantum modules by up to 49 per cent. This reduction in required modules translates directly into lower capital expenditure and operational costs for network providers.

Cost-effective quantum networks enabled by optimised fibre integration

The promise of unhackable communication via quantum key distribution (QKD) hinges on building networks capable of transmitting delicate quantum signals alongside everyday data. This work offers a pragmatic route, demonstrating that deliberately integrating hollow-core fibre, a new technology guiding light through air, with existing single-mode fibre can sharply lower deployment costs. However, simulations reveal a diminishing return on investment beyond a 40 per cent upgrade to hollow-core fibre, prompting further investigation into optimal network configurations. Simulations reveal that increasing the proportion of hollow-core fibre initially yields substantial benefits, but the cost savings plateau after reaching the 40 per cent threshold, indicating a point of diminishing returns. This is likely due to the interplay between the cost of the hollow-core fibre itself and the reduction in quantum module requirements. Further research could explore hybrid approaches, such as strategically placing hollow-core fibre only on critical links or utilising different types of hollow-core fibre with varying performance characteristics.

A substantial initial cost saving for deploying quantum-resistant networks is achieved by reducing the number of quantum modules needed by up to 49 per cent. This is particularly important given the current expense associated with quantum key distribution (QKD) technology. Quantum modules, which house the single-photon sources and detectors essential for QKD, represent a significant portion of the overall network cost. Reducing the number of these modules without compromising security or performance is therefore a crucial step towards widespread adoption. This establishes a viable strategy for integrating nascent quantum technologies with established fibre infrastructure. Networks can support both quantum key distribution and conventional data transmission by selectively deploying hollow-core fibre, which guides light through air to minimise signal loss, opening questions regarding the optimal balance between fibre types for diverse network designs. The research highlights the potential for a phased deployment strategy, where existing fibre infrastructure is gradually upgraded with hollow-core fibre, minimising disruption and capital expenditure. Future work should investigate the impact of different network topologies, traffic patterns, and quantum key distribution protocols on the optimal fibre mix. Furthermore, exploring the long-term reliability and maintainability of hollow-core fibre in real-world network environments is essential for ensuring the sustainability of quantum communication infrastructure.

The research demonstrated that partially upgrading optical networks with hollow-core fibre can reduce the number of quantum modules required by up to 49 per cent. This matters because quantum modules are a significant cost component of quantum key distribution technology, and reducing their quantity lowers the overall expense of deploying quantum-resistant networks. The study found cost savings plateaued after upgrading 40 per cent of links, suggesting an optimal balance between fibre types. Authors suggest further investigation into strategically placed hollow-core fibre and varying fibre performance characteristics could refine these findings.