MOONLIGHT

The MOONLIGHT project, led by the Istituto Nazionale di Fisica Nucleare (INFN), is at the forefront of developing innovative quantum communication systems that leverage the unique properties of light’s orbital angular momentum (OAM). Since its formal introduction in the late 20th century, OAM has opened new avenues in optics, giving rise to the field of singular optics. This area explores light beams with helical phase fronts, characterized by a quantum number ℓ, known as the topological charge, which quantizes the orbital angular momentum of individual photons as Lz = ℏℓ.

The high-dimensional nature of OAM states allows for encoding quantum information at significantly higher densities compared to traditional two-dimensional polarization states. This capability is particularly advantageous for quantum information applications, enabling more secure and efficient data transmission.

A central aim of the MOONLIGHT project is to develop, both theoretically and experimentally, a novel quantum communication protocol that utilizes only a small portion of the received beam to detect OAM states. This approach addresses practical challenges in real-world scenarios, such as atmospheric turbulence and alignment issues, by reducing the reliance on capturing the entire beam profile.

To facilitate this, the project employs a Parametric Down-Conversion (PDC) source capable of encoding information in the OAM variable. By utilizing a pulsed high-power laser, the PDC process generates a higher number of distinguishable photon pairs, enhancing the feasibility of long-distance quantum communication.

Complementing the quantum channel, a parallel classical communication system is integrated and synchronized with the quantum system. This classical channel plays a crucial role in selecting entangled photon pairs, ensuring the integrity and efficiency of the quantum communication process.

Furthermore, the project has optimized an effective OAM-state projection system and a local detector to increase the overall efficiency of the communication system. These advancements are critical for practical implementations, as they allow for more flexible and scalable detection architectures in quantum communication networks.

In summary, the MOONLIGHT project endeavors to:

• Develop a robust quantum communication protocol that leverages the high-dimensional encoding capabilities of OAM states.

• Demonstrate the feasibility of detecting OAM states using only a fraction of the received beam, addressing practical deployment challenges.

• Enhance the generation of entangled photon pairs through advanced PDC sources, facilitating long-distance quantum communication.

• Integrate classical communication channels to support the selection and synchronization of entangled photon pairs.

• Optimize detection systems to improve the overall efficiency and scalability of quantum communication networks.

Through these objectives, the MOONLIGHT project aims to contribute significantly to the advancement of quantum communication technologies, paving the way for secure and high-capacity quantum networks.