Entanglement is one of the main properties of quantum physics, which leads to very strong correlations between spatially separated systems. The distribution of entanglement between the nodes of a quantum network will allow new advances e.g. in long distance quantum communication, distributed quantum computing and quantum sensing. On the ground, quantum information can be distributed across the nodes using single photons at telecommunication wavelengths traveling in optical fibers. The maximal distance that can be reached in optical fibers with direct transmission is however limited to a few hundred km due to the loss in the fiber. In classical communications, this problem is solved by placing amplifiers every 50 to 100 km in the fiber network (so called repeaters). However, this kind of repeaters cannot be used with quantum bits, due to the unavoidable noise they produce. One solution to reach longer, continental distances is to use quantum repeaters which use entanglement between quantum memories as main building block.
In a study published in Nature that was featured on the cover of the issue, ICFO researchers led by ICREA Prof. Hugues de Riedmatten , have achieved entanglement between two solid-state quantum memories located in different laboratories 10 m appart. The entanglement was heralded by a photon at teleccomunication wavelength and stored in the quantum memories in a multiplexed fashion. These two key features have been achieved together for the first time and define the stepping stone in extending this scheme to much longer distances.
These results constitute an important milestone towards the practical realization of quantum repeaters using the installed fiber optic telecom network.
