6,944 research outputs found

    Dynamical Generation of Noiseless Quantum Subsystems

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    We present control schemes for open quantum systems that combine decoupling and universal control methods with coding procedures. By exploiting a general algebraic approach, we show how appropriate encodings of quantum states result in obtaining universal control over dynamically-generated noise-protected subsystems with limited control resources. In particular, we provide an efficient scheme for performing universal encoded quantum computation in a wide class of systems subjected to linear non-Markovian quantum noise and supporting Heisenberg-type internal Hamiltonians.Comment: 4 pages, no figures; REVTeX styl

    Towards optimized suppression of dephasing in systems subject to pulse timing constraints

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    We investigate the effectiveness of different dynamical decoupling protocols for storage of a single qubit in the presence of a purely dephasing bosonic bath, with emphasis on comparing quantum coherence preservation under uniform vs. non-uniform delay times between pulses. In the limit of instantaneous bit-flip pulses, this is accomplished by establishing a new representation of the controlled qubit evolution, where the resulting decoherence behaviour is directly expressed in terms of the free evolution. Simple analytical expressions are given to approximate the long- and short- term coherence behaviour for both ohmic and supra-ohmic environments. We focus on systems with physical constraints on achievable time delays, with emphasis on pure dephasing of excitonic qubits in quantum dots. Our analysis shows that little advantage of high-level decoupling schemes based on concatenated or optimal design is to be expected if operational constraints prevent pulses to be applied sufficiently fast. In such constrained scenarios, we demonstrate how simple modifications of repeated periodic echo protocols can offer significantly improved coherence preservation in realistic parameter regimes.Comment: 13 figures,1 tabl

    Nucleosynthesis of the chemical elements

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    Pengaruh Inventory Turnover, Total Asset Turnover Dan Net Profit Margin Terhadap Perubahan Laba Pada Perusahaan Manufaktur Yang Terdaftar Di Bursa Efek Indonesia

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    This study aims to analyze the effect of inventory turnover, total asset turnover, and net profit margin to changes in earnings in the automotive sector manufacturing companies listed in Indonesia Stock Exchange during the period 2010-2014. The research method in this study is a quantitative method by using financial statements to test the hypothesis that has been compiled to the variables to be studied. The results showed that the inventory turnover have a significant influence on changes in earnings is evidenced by the significant value of 0.014 0.05 and a net profit margin of significance value of 0.081> 0.05 it can be concluded that the total asset turnover and net profit margin does not have a significant effect on earnings changes. Significant value 0.019 <0.05 this proves inventory turnover, total asset turnover, and net profit margin simultaneously significant effect on the change in earnings in manufacturing automotive sector from 2010-2014 listed in the Indonesia Stock Exchang

    Introduction to Quantum Error Correction

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    In this introduction we motivate and explain the ``decoding'' and ``subsystems'' view of quantum error correction. We explain how quantum noise in QIP can be described and classified, and summarize the requirements that need to be satisfied for fault tolerance. Considering the capabilities of currently available quantum technology, the requirements appear daunting. But the idea of ``subsystems'' shows that these requirements can be met in many different, and often unexpected ways.Comment: 44 pages, to appear in LA Science. Hyperlinked PDF at http://www.c3.lanl.gov/~knill/qip/ecprhtml/ecprpdf.pdf, HTML at http://www.c3.lanl.gov/~knill/qip/ecprhtm

    Laser Based Underwater Communication Systems

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    We report on recent progress in the field of visible light communications including direct modulation of blue laser devices at data rates beyond 10 Gbit/s, and the transmission of 2.5 Gbit/s OOK data through water. We also discuss the advantages of operating with single mode laser devices and matched filtering at the receiver in the context of applications with significant solar background. The system performance for two types of direct-detection receivers, a PIN detector and less conventional silicon Photomultiplier technology will be presented
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