Polarization of light has been used extensively in quantum information processing, and quantum entanglement is essential to many areas of research, including quantum computing. Here we investigate the degree of polarization and the entanglement of a family of quantum states known as photon-added entangled coherent states. Such states could serve as means of entanglement distribution and quantum key distribution. Using the quantum Stokes parameters and the $Q$ function, we demonstrate that, in general, the degree of polarization of two two-mode photon-added coherent states increases significantly with the number of added photons. And using the concurrence, we show that the amount of entanglement in this kind of superposition presents a behavior that is dependent on whether or not the number of added photons in each mode is the same.

The aim of this work is to propose all-optical logic gates based on surface plasmon polaritons (SPP's) coupling among spatially separated graphene sheets. This model consists of graphene nanoribbons embedded in silica (SiO₂) substrate place in a distance such that allow an efficient coupling between the plasmonic modes of the waveguides. It was numerically analyzed the propagation's behavior of the SPP modes in an interferometric device as function of the chemical potential and geometrical parameters in order to obtain the AND/OR/XOR logic gates for OOK modulation.