January 16, 2025
Professor Roberto Morandotti’s team at Institut national de la recherche scientifique (INRS) has just taken a major step forward in quantum communications. Their discovery, published recently in the journal Nature Communications in partnership with colleagues at INRS and around the world, pushes even further the promising capabilities offered by the use of quantum information processing in telecommunications.
The system developed by the research team is based on a combination of the concepts of quantum key distribution and ultra-fast interval encoding. This breakthrough represents a first in the scientific world.
Breaking new ground
Quantum key distribution enables secret encryption keys to be exchanged that are known only to the parties sharing them, making them highly secure against potential attacks. It is a secure method of communication whose potential is recognized in the field of quantum computing.
“The idea behind our work was to check whether this potential could be enhanced by qudits. Thanks to the multiple values they can take on simultaneously, qudits make information travel faster than their cousins the qubits, which are photons that only take on the values 0 and 1”, explains Stefania Sciara.
The postdoctoral researcher adds that coding in time bins (the time window in which the photon is generated or detected) is already recognized as being advantageous for long-distance fiber-optic quantum communications, above all because of its robustness against sources of interference linked to propagation.
On the other hand, the interferometric diagrams used until now for processing high-dimensional time bins intervals tended to be unstable and inaccurate, which limited the processing speed and data transmission rate, keeping them far behind comparable ones used in standard telecommunications.
Challenges overcome and convincing data
To overcome this problem, Professor Morandotti’s team created a photonic platform coupled with fiber optics, comprising a cascade of interferometers and a source of entangled photons, both arranged in the same integrated circuit. “Our system has enabled us to manipulate high-dimensional time bins at processing speeds typical of standard telecommunications (10 GHz), with a high quantum information capacity per frequency channel,” explains the researcher.
The platform Professor Morandotti’s team has created made it possible to generate and process high-dimensional entangled photon states in time bins and distributed over the C-band, which is typical of telecommunications.
These results show that a protocol using high-dimensional entangled photons (qudits) offers greater security and speed than two-dimensional entangled photons (qubits). The broader potential of the model devised by the research team for secure quantum communications has been validated on a 60 km optical fiber.
These advances represent a major step towards the efficient implementation of high-data rate quantum communications in standard multi-user fiber optic networks. “Not only do they enable the use of quantum information processing in telecommunications, but they also demonstrate the potential of photonic states entangled in time bins to achieve high data rates and security levels for a variety of fiber optic quantum communication protocols over long distances,” adds the postdoctoral researcher.
These new security and speed standards have the practical and economic advantage of being compatible with existing telecommunications networks. Eventually, they could serve as a basis for developing the quantum computer that the scientific community has been working toward for several years.
About the study
Yu, H., Sciara, S., Chemnitz, M. et al. Quantum key distribution implemented with d-level time-bin entangled photons. Nat Commun 16, 171 (2025). https://doi.org/10.1038/s41467-024-55345-0
This research was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC), the Fonds de recherche du Québec (FRQ), Mitacs, China Scholarship Council (CSC), Conseil Régional Nouvelle-Aquitaine (the SPINAL project), and the European Research Council (ERC).
