Multimode Quantum Photonics

Building a quantum processor that we could use to solve real-world problems might constitute one of the most burning scientific questions and significant technological challenges of the beginning of the 21st century. Interestingly, recent results have indicated that quantum optics constitute a promising architecture for scalable quantum information processing. In this domain we are actively investigating new theoretical questions related to quantum information processing with high-dimensional photonic systems and their interplay with current technologies.

This research theme investigates research topics positioned at the frontier between quantum communications and classical coherent optical communications. It is in particular centered on the design of Continuous-Variable Quantum Key Distribution (CV-QKD) systems and their integration in modern optical networks.

The high-level objective of our work is to enable simultaneous transmission of Classical and QKD signals. In collaboration with Professor Yves Jaouen, from the Optical Telecommunication group of Télécom Paris, we perform experimental quantum communications demonstrations over a state-of-the art (40 Gb/s) optical coherent communication platform (cf photo).

We specifically tackle novel questions in the context of quantum communications, such as the use of DSP-based noise-control techniques and the convergence of classical and quantum communication systems design. This enables us to improve our ability to deploy quantum communications over a shared fiber in presence of intense classical WDM signals, but also to operate classical and quantum communications with shared hardware [AJW+22]. In the future, we aim to leverage digital signal processing and machine learning (ML) techniques to characterize and mitigate noise, paving the way for a seamless integration of quantum communications into modern optical networks.

As a complementary line of research, we intend to theoretically study multimode quantum coherent communications using multimode shaping of the local oscillator. We also intend to explore the possibility to rely on CV multimode encoding as a way to experimentally implement new quantum cryptographic constructions.

This work is supported by the European Quantum Technology Flagship projects CIVIQ and QSNP.

Building a quantum processor that we could use to solve real-world problems with practical benefits might constitute one of the most burning scientific and technological challenges of the beginning of the 21st century. A central conviction underpinning QURIOSITY project is that quantum photonics combined with digital technologies will play a leading role in unveiling the power of high-dimensional controllable quantum systems, and transition towards the demonstration of a useful quantum advantage for information processing tasks.

We investigate new theoretical questions related to quantum information processing (QIP) with high-dimensional photonic systems in close collaboration with leading experimental teams. We currently actively work on two projects, corresponding to two different experimental platforms: quantum frequency processor (in collaboration with Nadia Belabas, at C2N) and programmable linear circuits operating on a multimode fiber (in collaboration with Sylvain Gigan, at LKB).

In collaboration with the teams of Nadia Belabas and Pascale Senellart at C2N and in the context of the ParisQCI project, we study how to combine high-dimensional photonic gates, using the combined action of off-the-shelf telecom components such as Pulse Shapers and Electro-Optic Modulators (see Figure below), to efficiently synthesize high-dimensional unitary transformations. We have recently demonstrated in [HRR+22] the possibility to synthetize and to parallelize arbitrary single-qubit unitaries. We now intend to study how such systems could be leveraged for optical quantum information processing, and in particular for quantum metrology.

In collaboration with the team of Sylvain Gigan at ENS Ulm and in the context of the PhD of Francesco Mazzoncini (co-supervised by Romain Alleaume and Sylvain Gigan) we leverage the experimental platform multimode programmable linear circuit, to perform some fundamental demonstrations of quantum advantage in communication. This platform, built around a multimode fiber and spatial light modulators (cf. Figure below - credit: Complex Media Optics Lab), enables to approximately synthetize (up to some precision) any arbitrary high-dimensional unitary, and can hence be used to emulate an arbitrary linear network.

Our current work on the experimental demonstration of a quantum advantage in communication has interesting connection to Bell inequality and may open a paths towards experimentally demonstrating robust Bell inequality violations. It moreover has natural applications in cryptography and physical layer security, that we are already starting to investigate.