Daniele Dequal

We propose Qubit4Sync, a synchronization method for Quantum Key Distribution (QKD) setups, based on the same qubits exchanged during the protocol and without requiring additional hardware other than the one necessary to prepare and measure the quantum states, in a similar fashion to the clock recovery used in classical communications. Our approach introduces a new cross-correlation algorithm achieving the lowest computational complexity, to our knowledge, for high channel losses. We tested the robustness of our scheme in a real QKD implementation, and we believe it may find application in other quantum communication protocols

Space-based quantum key distribution would allow, in the near future, secure communications be- tween parties over continental distances, complementing short-range fiber-based quantum networks. However, further demonstrations of daylight operations over free-space channels and the full compatibility with the telecom-based fiber infrastructure are still necessary. Here we present the prototype for daylight QKD at 1550 nm we developed as a demonstrator for application of QKD both on ground and in Space. Our QKD source, exploiting integrated silicon photonics technology, allows to reach a QBER of 1% during the field-test performed over a 145 m link, and represents a promising resource to design quantum optical payloads to be implemented in future satellite missions.

In this study, we constructed a full end-to-end atmospheric channel model for a GEO quantum exchange. This model allowed to assess the performances of two MDI-QKD protocols in such conditions : MP-QKD and TF-QKD, thus setting the limits of these protocols with current and future technology on detection, emission and optic tools. We demonstrated that an untrusted GEO link between two independent parties can be achieved when using reasonable size of telescope diameter. The key rates predicted would allow transmitting up to 260 bit/s for TF-QKD and up to 180 bit/s for MP-QKD for a telescope pupil diameter of 1m at 2.5 GHz of repetition rate.