How to send entangled photons across hundreds of km? A multimode platform for near-term quantum repeaters

Cleverly utilized, quantum theory can tremendously enhance a broad range of optical technologies from secure communication and distributed computing to super-resolved imaging. In particular, pairs of photons can be easily produced in quantum entangled states of their polarizations – Bell states. Such states yield a non-local property. Measuring polarization of one photon gives a random result, but then the other is always found in the orthogonal polarization. While of many applications, entangled photonic states are also very fragile. After transmission through 100 km of telecom (1500 nm) fiber only ca. 1% of the photons survive and an entangled state cannot be directly amplified. As a solution quantum repeaters (QR) have been proposed and demonstrated [1] .