Alberto Boaron

To enable the widespread use of Quantum Key distribution, network integration is crucial. We present a case study where we investigate the performance of a 2.5 GHz simplified BB84 implementation using a wavelength of 1310nm multiplexed in a fiber together with 13 classical channels. We found that a secret key exchange at a distance of 95.5km and classical launch power up to 8.9dBm was possible. Further, we compare our results to previous results, both for continuous variable systems using a wavelength of 1550nm and discrete variable systems using either a wavelength of 1550nm or 1310nm. We find that both for long distance and for high power in the classical channels, the discrete variable systems perform better.

Integrating Quantum Key Distribution (QKD) into optical metropolitan networks is a crucial step toward bringing quantum technologies into existing telecommunication fiber infrastructures. However, current state-of-the-art solutions still face major challenges, including their sensitivity to classical noise, especially spontaneous Raman scattering, limited transmission distances, and performance degradation under heterogeneous network conditions. In this work, we present a new QKD system operating in the O-band at 1295.56 nm, where the effect of the main noise sources is significantly reduced. Combined with narrow spectral filtering at the receiver, without the need for active temperature control, the system shows strong robustness across a wide range of dense wavelength division multiplexing scenarios, making it a practical option for real-world deployment. We validate its performance through extensive testing and demonstrate stable key generation while coexisting with different classical traffic conditions, with total launch powers of up to 17 dBm. These results represent an important step forward for the integration of QKD into existing fiber networks, supporting the path toward secure quantum communications at scale.

We investigate a class of partially device-independent quantum key distribution protocols based on a prepare-and-measure setup which simplifies their implementation. The security of the protocols is based on the assumption that Alice’s prepared states have limited overlaps, but no explicit bound on the Hilbert space dimension is required. The protocols are therefore immune to attacks on Bob’s device, such as blinding attacks. The users can establish a secret key while continuously monitoring the correct functioning of their devices through observed statistics. We report a proof- of-principle demonstration, involving mostly off-the-shelf equipment, as well as a high-efficiency superconducting nanowire detector. A positive key rate is demonstrated over a 4.8km low-loss optical fiber with finite-key analysis. The prospects of implementing these protocols over longer distances is discussed.

We implement 5 GHz clocked polarization-based simplified BB84 protocol. Secret keys can be distributed over 151.5 km of standard telecom fiber at a rate of 54.5 kbps. The high clock frequency might give rise to correlations between the pulses. We characterize the correlations in decoy intensity, polarization and in the phase between the pulses and discuss their impact on the security of the protocol.