🔒 A quantum cryptography protocol integrating a quantum memory

Scientists have successfully added a quantum storage layer to a cryptography protocol, an essential step for the practical use of the encryption properties offered by quantum mechanics.

Quantum memories are expected to play a central role in future quantum networks, as they allow information to be stored and retrieved on demand. While their utility for entanglement distribution and long-distance communications is well established, their potential extends far beyond this framework.


Researchers have just demonstrated for the first time that a quantum memory can be integrated into a cryptography protocol. This demonstration is the result of a fruitful collaboration between two projects of the Quantum PEPR, the QMemo project and the QCommTestBed project.

The chosen protocol is that of "quantum money", proposed nearly forty years ago by Stephen Wiesner and guaranteeing complete unforgeability for banknotes using this validation protocol. The major innovation here lies in the introduction of a storage step: the customer's "quantum card" is kept in a memory before being used. The first demonstrations of quantum money were essentially proof-of-principle experiments performed on the fly, without any storage step.

However, for a quantum banknote or card to be used effectively—for example for deferred payment or remote verification—it is necessary to integrate a memory that ensures the temporary preservation of quantum states. This result was only possible thanks to the unprecedented performance of the implemented memory—a set of laser-cooled cesium atoms—combining very high storage efficiency with extremely low noise. These performances make it possible to guarantee the security thresholds required for future applications, which had until now remained out of reach.

This breakthrough shows that quantum memories have now reached a degree of maturity that allows for their deployment in concrete applications. They are no longer limited to a role of preserving information in quantum repeaters, but are gradually becoming versatile tools for quantum networks. These results are published in the journal Science Advances.