We published a first pre-print within the new research line led by Dr. Dario A. Fioretto! The BB84 protocol is a major quantum key distribution (QKD) protocol allowing to share cryptographic keys encoded in the polarization of single photons. We investigated the performances of BB84, already implemented with dim laser pulses and single photons, using hybrid photon-number statistics obtained by incoherently mixing both types of light. The single-photon purity and brightness of our quantum dot source coupled with a precise and flexible control of the laser intensity allow us to optimize the rate of shared secret bits of information for a wide range of distances between the two users. Additionally, our extensive study of these hybrid statistics brings a new understanding of advantage scenarios of practical single-photon sources over laser pulses, paving the way for concrete and efficient implementations using quantum dots.
Distance scaling of the secret key rate obtained with different hybrid statistics. Secret key rate is the basic figure of merit for QKD protocols, indicating the amount of bits shared by Alice and Bob that can be used in a final key per unit of time.
Tuning the amount of laser represented by its mean photon number reveals that it is possible to optimize the SKR for every distance, benefiting both from the long-distance scaling of single photons and the high rate at short distance of the laser pulses. We managed to perform key distribution over what would be equivalent to more than 140 km!
Y. Portella, P. Steindl, JR Álvarez, T. Hebenstreit, A. Lemaître, M. Morassi, N. Somaschi, L. Lanco, F. Rozpędek, P. Senellart, DA. Fioretto, “Benchmarking quantum key distribution by mixing single photons and laser light,” arXiv:2510.26337 (2025)