By using the partial wave method, we investigate the absorption of massless scalar wave from regular black hole. We numerically carry out the absorption cross section and find that the larger angular momentum quantum number is, the smaller the corresponding maximum value of partial absorption cross section is. Comparing with Schwarzschild case, the absorption cross section of regular black holes is strengthened in both low and high frequency regions, and the absorption cross section oscillates around the geometric optical value in the high frequency region. Generally speaking, the scattering flux is strengthened and its scattering width becomes narrower in the forward direction. There are obvious contrast of scattering properties of different type of regular black hole.

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We analyze the Schrödinger-type scalar wave equation of an extended black hole in 𝑓 (𝑅) gravity, and numerically investigate its absorption/scattering cross sections using the partial wave method. It is found that the dimension of length 𝛼 makes the peak value of the effective scattering potential fall down, and the absorption cross section oscillates around the geometric optical value in the high frequency regime. We can also see that the scattering flux becomes stronger and its angle width becomes narrower in the forward direction, the glory peak becomes lower and the glory width becomes narrower along the backward direction when the coupling parameter 𝛼 increases.

In this paper, we study single-qubit and single-user quantum repeaters based on CNOT gates under decoherence using the Kraus-operator representations of decoherence. We investigate the influence of decoherence on the information-disturbance trade-off of quantum repeaters. It is found that decoherence may lead to the appearance of three subspaces, called as the normal subspace, the anomalous subspace, and the decoherence-free subspace (DFS), respectively. It is indicated that in the normal subspace decoherence decreases the transmission and estimation fidelities, in the anomalous subspace decoherence enhances these fidelities, and in the DFS these fidelities do not change. The concept of the quality factor is introduced to evaluate the quality of the quantum repeater. It is indicated that the quality factor can be efficiently controlled and manipulated by changing the initial state of the probe qubit. It is found that under certain conditions the quantum repeater can be optimal even in the presence of decoherence.