Implementation of space-division multiplexed entanglement-based quantum cryptography over multicore fiber

Quantum communication implementations require efficient and reliable quantumchannels. Optical fibers have proven to be an ideal candidate for distributingquantum states. Thus, today's efforts address overcoming issues towards highdata transmission and long-distance implementations. Here, we experimentallydemonstrate the secret key rate enhancement via space-division multiplexingusing a multicore fiber. Our multiplexing technique exploits the momentumcorrelation of photon pairs generated by spontaneous parametricdown-conversion. We distributed polarization-entangled photon pairs intoopposite cores within a 19-core multicore fiber. We estimated the secret keyrates in a configuration with 6 and 12 cores from the entanglement visibilityafter transmission through 411 m long multicore fiber.