Daniele Cozzolino

We experimentally tested an alternative fiber-based setup for 4D-QKD, with time and phase encoding and one-decoy technique. We evaluated the secret key rate achievable in a finite-key scenario and we compared it with the binary-encoded BB84 protocol, which was tested with the same experimental setup. Our 4D-QKD system makes it possible to improve the secret key rate by more than a factor 2 in the saturation-regime of single-photon detectors, without requiring additional expensive resources to the 2D-QKD setup. In comparison to previous works, our scheme allows to measure the 4D states with a simplified and compact receiver, thus making it a cost-effective solution for practical and fiber-based QKD.

High-dimensional quantum key distribution (QKD) with path-encoded qudits can largely benefit from the slower phase drifts characteristic of multicore fibers: however, such channels still require phase stabilisation systems to effectively transmit quantum states with an acceptable error rate. We propose a scheme that multiplexes a co-propagating wavelength to use as reference signal in a phase locked loop system, and simultaneously achieves state of the art repetition rates for the high-dimensional QKD system. These factors allow us to design a system that can reach a much higher secret key generation rate over a propagation distance that is order of magnitudes longer than what shown in previous results, making our path-encoded QKD system appealing and comparable in terms of performance with current quantum systems.