Mutual preservation of entanglement

Katarzyna Siudzińska, Dariusz Chruściński

A new family of positive, trace-preserving maps is introduced. It is defined using the mutually unbiased measurements, which generalize the notion of mutual unbiasedness of orthonormal bases. This family allows one to define entanglement witnesses whose indecomposability depends on the characteristics of the associated measurement operators. We provide examples of indecomposable witnesses and compare their entanglement detection properties with the realignment criterion.

Muhammed Ashefas, T. M. Manosh, R. B. Thayyullathil

We study two coupled cavities with a single two-level system in each and a second-order non-linear process in one of the cavities. Introduction of a harmonic time dependence on the non-linear coupling is utilized for the preservation of dynamics. It is observed that, even though the preservation period is independent of the initial state, the preserved dynamics depends on the initial state. We calculated the von Neumann entropy and mutual information to study the entanglement present between the subsystems. From which it is found that the time-dependent coupling also preserves the entanglement produced in the system.

Fuli Li, Muhammad Suhail Zubairy

Özenç Güngör, S. Turgut

In this paper, the following scenario is considered: there are two qubits possessed by two parties at different locations. Qubits have been prepared in one of a maximum of four, mutually-orthogonal, entangled states and the parties wish to distinguish between the states by using local operations and classical communication. Although in general it is not possible to distinguish between four arbitrary states, the parties can spend some preshared entanglement to achieve perfect discrimination between four qubit states and can also preserve the entanglement of the states after discrimination. This is shown by employing the theory of majorization and the connections between entanglement transformations and state discrimination protocols.