Physicists at Heriot-Watt University in Edinburgh, Scotland, have marked a significant advancement in quantum communications by successfully routing and teleporting entangled states of light across two four-user quantum networks. This achievement, led by researchers Mehul Malik and Natalia Herrera Valencia, introduces a novel method that utilizes light-scattering processes in standard optical fibres, paving the way for scalable quantum communication systems.
The team’s innovative approach diverges from conventional photonic chip methods, allowing for a programmable entanglement router capable of adapting to various network configurations on demand. The experiments employed commercially available optical fibres, which are multi-mode structures that scatter light via random linear optical processes. As explained by Herrera Valencia, this means that light travels chaotically through the fibres, taking numerous internal pathways. While such scattering can disrupt entanglement, researchers at the Institut Langevin in Paris, France, have previously determined that the effects of this scrambling can be analyzed through the fibre’s light transmission characteristics.
This technique leverages the light-scattering processes to create programmable optical circuits, simplifying the circuit architecture by separating the layers where light is controlled from those where it is mixed. The use of waveguides for manipulating quantum states of light significantly reduces optical losses. Consequently, the researchers developed a reconfigurable multi-port device capable of distributing quantum entanglement among multiple users simultaneously. This device can switch between various channels, such as local and global connections, as required.
Another noteworthy aspect of this advancement is its multiplexing capability, which allows several quantum processors to utilize the system concurrently. This is akin to multiplexing in classical telecommunications, where vast amounts of data can be transmitted through a single optical fibre using distinct light wavelengths.
Despite the progress, Malik notes that controlling and distributing entangled states of light presents challenges. Traditional methods reliant on photonic chips struggle with scalability and are particularly sensitive to manufacturing imperfections. The Heriot-Watt team’s waveguide-based approach “opens up access to a large number of modes, providing significant improvements in terms of achievable circuit size, quality and loss,” Malik stated. This method also aligns well with existing optical fibre infrastructures.
Achieving precise control over the complex scattering processes inside the waveguide was no easy feat. Herrera Valencia highlighted the steep learning curve involved in mastering the manipulation of quantum states of light within such a complicated medium. “It took time and iteration, but we now have the precise and reconfigurable control required for reliable entanglement distribution, and even more so for entanglement swapping, which is essential for scalable networks,” she explained.
Looking forward, the researchers aim to explore larger-scale circuits capable of operating on more photons and light modes. They believe that the technique they have developed could also facilitate the implementation of extensive photonic circuits with applications that range from machine learning to quantum computing and networking. Malik expressed a desire to transition some of their network technology from the laboratory into practical use, with Herrera Valencia leading efforts in commercialization.
The findings from this research were published in Nature Photonics, underscoring the significance of this milestone in the field of quantum networking, which could revolutionize communication technologies in the future.
