Future quantum networks offer the potential for new communication and computation applications. These quantum networks will undoubtedly require the routing of quantum information between distant parties. In order to reliably achieve the transmission of entangled states over such a network, some entanglement distillation protocol can be implemented on an ensemble of entangled photon pairs. Here, we demonstrate such a protocol by recovering quantum information using local filters on each photon of a polarization-entangled state in the presence of a common source of decoherence in the telecom fiber infrastructure, polarization mode dispersion (PMD).
We present a study of nonlocal polarization-mode dispersion (PMD) compensation in the framework of quantum information theory. We consider distribution of polarization-entangled photon pairs through optical fibers, where PMD acts as a decoherence mechanism. The use of additional controlled PMD in one of the two optical paths can restore the original degree of entanglement fully or in part, depending on the system configuration, in a nonlocal fashion. Using the quantum analog of the Shannon entropy, the Von Neumann entropy, we evaluate the quantum mutual information of propagated polarization-entangled photon pairs as a function of the fiber-channel PMD, and quantify the beneficial effect of nonlocal PMD compensation in terms of mutual quantum information restoration. All the relevant quantities can be extracted from the reduced density matrix characterizing the twophoton state polarization, which is obtained experimentally by means of customary polarization tomography.