Atomic spin‐wave (SW) memory is a building block for quantum repeater. However, due to decoherence caused by atomic motions and magnetic‐field gradients, SW retrieval efficiency decays with storage time. Slow magnetic‐field fluctuations (SMFFs) lead to shot‐to‐shot phase noises of SWs, but have not been considered in previous repeater protocols. Here, a SW model including a homogeneous phase noise caused by SMFFs is developed, and then revealed that such phase noise induces decoherence of single‐excitation entanglement between two atomic ensembles in a repeater link. For verifying this conclusion, single‐excitation entanglement between two SWs in a cold atomic ensemble is experimentally prepared and observed entanglement decoherence induced by SMFFs. Limited by SMFFs, the evaluated lifetime of the single‐excitation entanglement over a repeater link is ≈135 ms, even if the link uses optical‐lattice atoms as nodes. Then an approach that may overcome such limitations and extend this lifetime to ≈1.7 s is presented.
The power supply of electronic equipment is significant and have important function in electronic field. In this paper, a detection system of switch power supply based on DSP is introduced. The system can detect the duty-ratio of capacity value, inductance value, resistance value,output voltage value,diode voltage drop and current pulse-width modulation chip on PCB of switch power supply. Consequently, it finishes the real-time detection on PCB and it is significant to research the fault analysis of switch power supply. The schematic diagram and the outside circuit schematic diagram based on DSP is given in the paper. In the meanwhile, the system accomplishes the data selecting and setting of lower computer by using LabVIEW upper computer. The system has the universality to electrical industry.
It is significant to the whole system or its connected network and to run safely and steadily by detecting and cutting out faults fast and accurately. In this paper, a new transient signal analysis method is got based on the Hilbert-Huang Transform conversion. It’s original is that by making simulation on interior and external district of direct current through HVDC transmission model, and using MATLAB to analyze transient voltage signal on every fault, and then a protection project of high voltage direct transmission line is proposed based on HHT. The simulation results show that the scheme overcomes the inherent defects of the traditional algorithm, and makes up for the shortage that the protection is easily affected by the transition resistance and can not be accurately judged when the ground fault occurs, which effectively improves the detection accuracy and speed of the line protection.
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