Multipartite entanglement of fermionic systems in noninertial frames

The bipartite and tripartite entanglement of a 3-qubit fermionic system when one or two subsystems accelerated are investigated. It is shown that all the one-tangles decrease as the acceleration increases. However, unlike the scalar case, here one-tangles ${\cal N}_{C_I(AB_I)}$ and ${\cal N}_{C_I(AB)}$ never reduce to zero for any acceleration. It is found that the system has only tripartite entanglement when either one or two subsystems accelerated, which means that the acceleration doesn't generate bipartite entanglement and doesn't effect the entanglement structure of the quantum states in this system. It is of interest to note that the $\pi$-tangle of the two-observers-accelerated case decreases much quicker than that of the one-observer-accelerated case and it reduces to a non-zero minimum in the infinite acceleration limit. Thus we argue that the qutrit systems are better than qubit systems to perform quantum information processing tasks in noninertial systems.Comment: 12 pages, 3 figure

Shadow of a Schwarzschild black hole surrounded by a Bach-Weyl ring

We have studied the shadows of a Schwarzschild black hole surrounded by a Bach-Weyl ring through the backward ray-tracing method. The presence of Bach-Weyl ring leads to that the photon dynamical system is non-integrable and then chaos would appear in the photon motion, which affects sharply the black hole shadow. The size and shape the black hole shadow depend on the black hole parameter, the Bach-Weyl ring mass and the Weyl radius between black hole and ring. Some self-similar fractal structures also appear in the black hole shadow, which originates from the chaotic lensing. We also study the change of the image of Bach-Weyl ring with the ring mass and the Weyl radius. Finally, we analyze the invariant manifolds of Lyapunov orbits near the fixed points and discuss further the formation of the shadow of a Schwarzschild black hole with Bach-Weyl ring.Comment: 16 pages,8 figures, the version published in EPJ