Ortega et al. experimentally demonstrated the multiplexing of quantum signals by space-division multiplexing over a multicore fiber. To this end, they generated polarization-entanglement photon pairs at telecommunication wavelengths and distributed several pairs simultaneously and independently through 6 and 12 cores of the multicore fiber. Exploiting quantum correlations in different degrees of freedom of the generated photon pairs, the researchers deterministically coupled and transmitted entangled photons pairs through dedicated cores of the multicore fiber. In this way, the polarization-entangled photon pairs were efficiently coupled into opposite cores of the centrally-symmetric multicore fiber. Ortega and collaborators certified the high quality of this separation through intensity-correlations measurements between the different cores and high fidelity in the polarization measurements for the spatially correlated cores, implementing deterministic multiplexing up to twelve cores simultaneously.

The presented method allows to increases the data transmission in quantum communication protocols drastically by exploiting otherwise unused quantum correlations. In combination with other quantum multiplexing and encoding techniques, this approach provides a pathway towards high-rate quantum communication for the future quantum internet.