4-Dimensional Quantum Key Distribution Protocol over 52-km Deployed Multicore Fibre

We demonstrate a 4-dimensional path-encoded QKD system over a 52-km multi-core fieldinstalled fibre. The 4D-QKD has a 68.5 kbit/s secret key rate, which is 118% higher than the equivalent 2D-QKD over the same link, owing to the higher dimensionality and greater noise resilience.