  Entanglement distillation is a process via which the strength and purity of
quantum entanglement can be increased probabilistically. It is a key step in
many quantum communication and computation protocols. In particular,
entanglement distillation is a necessary component of the quantum repeater, a
device which counters the degradation of entanglement that inevitably occurs
due to losses in a communication line. Here we report an experiment on
distilling the Einstein-Podolsky-Rosen (EPR) state of light, the workhorse of
continuous-variable entanglement, using the technique of noiseless
amplification. In contrast to previous implementations, the entanglement
enhancement factor achievable by our technique is not fundamentally limited and
permits recovering an EPR state with a macroscopic level of entanglement no
matter how low the initial entanglement or how high the loss may be. In
particular, we recover the original level of entanglement after one of the EPR
modes has passed through a channel with a loss factor of 20. The level of
entanglement in our distilled state is higher than that achievable by direct
transmission of any state through a similar loss channel. This is a key
bench-marking step towards the realization of a practical continuous-variable
quantum repeater and other CV quantum protocols.
