Decoherence-free subspace and entanglement sudden death of multi-photon polarization states in fiber channels

The construction of quantum networks requires long-distance teleportation of multi-qubit entangled states. Here, we investigate the entanglement dynamics of GHZ and W states in fiber channels. In a fiber channel, the two most important phenomena that affect polarization entanglement are polarization mode dispersion (PMD) and polarization-dependent loss (PDL). We theoretically characterize how PMD and PDL vectors affect three-qubit states. In particular, upon quantifying the entanglement at the output states using concurrence and entanglement witness, we reveal the occurrence of entanglement sudden death (ESD) and the appearance of decoherence-free subspaces (DSFs) in tripartite systems. Finally, we explore the evolution of GHZ and W state with an arbitrary number of photons in a fiber network and evaluate the expectation value of the entanglement witness.