Pulsar interpretation of the lepton spectra measured by AMS-02

AMS-02 recently published its lepton spectra measurement. The results show that the positron fraction no longer increases above $\sim$200 GeV. The aim of this work is to investigate the possibility that the excess of positron fraction is due to pulsars. Nearby known pulsars from ATNF catalogue are considered as a possible primary positron source of the high energy positrons. We find that the pulsars with age $T\simeq (0.45\sim4.5)\times10^{5}$ yr and distance $d<0.5$ kpc can explain the behavior of positron fraction of AMS-02 in the range of high energy. We show that each of the four pulsars --- Geminga, J1741-2054, Monogem and J0942-5552 --- is able to be a single source satisfying all considered physical requirements. We also discuss the possibility that these high energy $e^{\pm}$ are from multiple pulsars. The multiple pulsars contribution predicts a positron fraction with some structures at higher energies.Comment: 27 pages, 5 figures, 3 tables, accepted for publication in EPJ

Robust quantum repeater with atomic ensembles and single-photon sources

We present a quantum repeater protocol using atomic ensembles, linear optics and single-photon sources. Two local 'polarization' entangled states of atomic ensembles $u$ and $d$ are generated by absorbing a single photon emitted by an on-demand single-photon sources, based on which high-fidelity local entanglement between four ensembles can be established efficiently through Bell-state measurement. Entanglement in basic links and entanglement connection between links are carried out by the use of two-photon interference. In addition to being robust against phase fluctuations in the quantum channels, this scheme may speed up quantum communication with higher fidelity by about 2 orders of magnitude for 1280 km compared with the partial read (PR) protocol (Sangouard {\it et al.}, Phys. Rev. A {\bf77}, 062301 (2008)) which may generate entanglement most quickly among the previous schemes with the same ingredients.Comment: 5 pages 4 figure