Integrated high-dimensional Quantum Key Distribution system for communication networks (InQKD)

Encryption is crucial in modern life for securing information and ensuring safe communication across digital platforms. Quantum encryption offers unprecedented security by leveraging the principles of quantum mechanics to create unbreakable encryption keys, making it essential for future-proofing data protection.

However, the realisation of mature quantum encryption systems requires scaling up of photonic platforms. Several thin-film fabrication methods such as lithography, and etching, have been used to fabricate nanophotonic devices. Nonetheless, these techniques are often complex, time-consuming, and expensive.

They require extensive prototyping and suffer from a lack of reproducibility, which can hinder large-scale production and practical implementation. Additionally, these traditional methods offer limited flexibility in correcting manufacturing defects, further complicating the production process.

In contrast, the two-photon polymerisation (2PP) technique offers a rapid, efficient, and highly reproducible alternative for fabricating photonic devices. The 2PP technique utilizes a focused laser beam to induce polymerization at the focal point, enabling precise 3D structuring at the nanoscale. This method allows for in-plane and out-of-plane printing, providing versatile substrate options and the ability to easily erase and reprint structures if necessary.

The rapid prototyping capability of 2PP significantly reduces production time and costs, making it an ideal choice for developing integrated photonic devices.

In this project, we are planning to use the 2PP technique to print a polymer strip on top of a thin film of lithium niobate. The polymer strip will confine light within the lithium niobate. Within this structure, pump laser light will be converted into photon pairs through spontaneous parametric down-conversion (SPDC) process.

SPDC is a nonlinear optical process where a photon from the pump laser is converted into two lower-energy entangled photons. These entangled photon pairs are essential for QKD, as they enable the creation of secure encryption keys based on the principles of quantum mechanics.

The successful development of this integrated quantum light source will represent a significant advancement in the field of quantum communication. By providing a compact, efficient, and readily deployable source of entangled photons, this project paves the way for the realization of robust and secure QKD networks. These networks leverage the fundamental properties of quantum mechanics to ensure the absolute security of transmitted information, making them immune to eavesdropping and other cyber threats.

Moreover, the implementation of 2PP in fabricating the quantum light source addresses the limitations of conventional fabrication methods, offering a scalable and cost-effective solution for mass production.