Implementing of high efficiency quantum teleportation protocols is in the key task for development of accessible and secure quantum communication. For a successful quantum teleportation two conditions should be satisfied: fidelity of teleportation greater then 1/2 for pure states and the existence of the entanglement between resource state modes during all teleportation process. Quantum teleportation using Gaussian states is a perspective direction because they can be easily implemented and manipulated using laser radiation. The simplest case for the continuous variable quantum teleportation represent teleportation of a pure state. However the thermal noise cannot be eliminated from the system, and the thermal component should be taken into account. In this work we put in evidence how the increase of average thermal photon number influence the fidelity of teleportation of a Gaussian state. We use Lindblad master equation and covariance matrix formalism to describe the temporal evolution of studied system and to put in evidence dependence of the fidelity of teleportation on the environment conditions and resource state parameters. As well we calculated the entanglement between the resource state modes to check if all conditions for a successful teleportation are satisfied.
Strongly coupled, highly dissipative arrays of Josephson junctions are characterized by presence of two branches for the currents greater then the critical one in their IV characteristic. Additional branch, called traveling wave branch is characterized by low voltage, generation of charge density waves in the stack. Traveling wave branch appears on the IV characteristic only if coupling and dissipation parameters have the values above their thresholds. In this work we focused on the study of charge density waves behavior in the specified type of Josephson junction arrays in order to explain the stability of the traveling wave branch. Were performed numerical simulations using Capacity Coupled Josephson Junctions with Diffusion Current (CCJJ+DC) model which gives good agreement with the experimental results and were obtained IV-characteristics and charge density temporal evolution profiles for different currents corresponding to traveling wave branch. Was shown that the form of charge density waves changes with the increase of current. Moreover was studied spectral structure of charge density waves and dependence of Lissajous correlations between charge accumulated on the neighbor superconducting layers on the current. thought the stack.
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