Experimental on-demand recovery of entanglement by local operations within non-Markovian dynamics

In many applications entanglement must be distributed through noisy communication channels thatunavoidably degrade it. Entanglement cannot be generated by local operations and classical communication(LOCC), implying that once it has been distributed it is not possible to recreate it by LOCC. Recovery ofentanglement by purely local control is however not forbidden in the presence of non-Markovian dynamics,and here we demonstrate in two all-optical experiments that such entanglement restoration can even beachieved on-demand. First, we implement an open-loop control scheme based on a purely local operation,without acquiring any information on the environment; then, we use a closed-loop scheme in which theenvironment is measured, the outcome controling the local operations on the system. The restoredentanglement is a manifestation of ‘‘hidden’’ quantum correlations resumed by the local control. Relying onlocal control, both schemes improve the efficiency of entanglement sharing in distributed quantumnetworks.