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Li J.,Peking University | Chen J.,State Key Laboratory of Precision Spectroscopy | Zeng H.,State Key Laboratory of Precision Spectroscopy | Li H.,Peking University
Progress in Electromagnetics Research Symposium | Year: 2013

Nowadays, quantum secure communication has been recognized as one of the most secure communication techniques, and plug-play scheme is one of the most practical case in QKD (quantum key distribution) experiment. This paper mainly introduces how to use FPGA (field programming gate array) to control the optical components in order to implement quantum key distribution system. The system works based on phase coding mode with optical pulse frequency being 10 MHz, communication distance being 50 km, code generating rate being 2 kbps and error rate being 10-6. Also we have developed an application software which can take text chat and secure file transmit for the QKD hardware system using Qt IDE on Linux OS. Copyright © 2013 The Electromagnetics Academy. Source


Liang Y.,State Key Laboratory of Precision Spectroscopy | Ren M.,State Key Laboratory of Precision Spectroscopy | Wu E.,State Key Laboratory of Precision Spectroscopy | Wang J.,East China Normal University | And 2 more authors.
IEEE Photonics Technology Letters | Year: 2012

We demonstrate a high-speed photon-number-resolving detector based on a sinusoidally gated multipixel photon counter (MPPC) at a repetition rate of 200 MHz. Two steps of low-pass filters are used to minimize the MPPC's capacitive response noise in sinusoidally gated Geiger mode, resulting in the efficient detection of weak photon-induced avalanche currents. Compared with passive quenching schemes, the sinusoidal gating scheme is conducive to shortening the recovery time for each pixel of the MPPC to detect the next coming photons, thus improving the detector's photon-number-resolving capability at a high repetition rate. The gated MPPC can identify the photon numbers of the incident pulses with a repetition frequency of 50 MHz clearly at as high as an average of 7.22 photons/pulse detected before saturation at room temperature. © 1989-2012 IEEE. Source


Duan L.L.,Shandong Normal University | Gao Y.,State Key Laboratory of Precision Spectroscopy | Ji C.G.,State Key Laboratory of Precision Spectroscopy | Mei Y.,State Key Laboratory of Precision Spectroscopy | And 3 more authors.
Science China Chemistry | Year: 2014

MD simulation study of several peptides including a polyalanine, a helix (pdb:2I9M), and a leucine zipper were carried out to investigate hydrogen bond energetics using dynamic polarized protein-specific charge (DPPC) to account for the polarization effect in protein dynamics. Results show that the backbone hydrogen-bond strength is generally correlated with its specific local electrostatic environment, measured by the number of water molecules near the hydrogen bond in the first solvation shell. The correlation coefficient is found to be 0.89, 0.78, and 0.80, respectively, for polyalanine, 2I9M protein, and leucine zipper. In the polyalanine, the energies of the backbone hydrogen bonds are very similar to each other due to their similar local electrostatic environment. The current study helps demonstrate and support the understanding that hydrogen bonds are stronger in a hydrophobic surrounding than in a hydrophilic one. For comparison, the result from simulation using standard force field shows a much weaker correlation between hydrogen bond energy and local electrostatic environment due to the lack of polarization effect in the force field. © 2014 Science China Press and Springer-Verlag Berlin Heidelberg. Source

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