18세기 의관 이수기(李壽祺)의 자기인식
01 Aug 2013-Vol. 22, Iss: 2, pp 483-527
About: The article was published on 2013-08-01 and is currently open access. It has received 303 citations till now.
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TL;DR: A variational method to efficiently simulate the nonequilibrium steady state of Markovian open quantum systems based on variational Monte Carlo methods and on a neural network representation of the density matrix is developed.
Abstract: The possibility to simulate the properties of many-body open quantum systems with a large number of degrees of freedom (d.o.f.) is the premise to the solution of several outstanding problems in quantum science and quantum information. The challenge posed by this task lies in the complexity of the density matrix increasing exponentially with the system size. Here, we develop a variational method to efficiently simulate the nonequilibrium steady state of Markovian open quantum systems based on variational Monte Carlo methods and on a neural network representation of the density matrix. Thanks to the stochastic reconfiguration scheme, the application of the variational principle is translated into the actual integration of the quantum master equation. We test the effectiveness of the method by modeling the two-dimensional dissipative XYZ spin model on a lattice.
198 citations
Tennessee Technological University1, National Institute of Standards and Technology2, University of California, Los Angeles3, Vanderbilt University4, University of Aberdeen5, Oklahoma State University–Stillwater6, University of Maryland, College Park7, Purdue University8, Rice University9, University of Wisconsin–Milwaukee10, Marshall Space Flight Center11
TL;DR: This paper envisions what the 21st century holds in store for OPC in terms of the driving forces that will shape the continued use of this material.
Abstract: In a book published in 1906, Richard Meade outlined the history of portland cement up to that point1. Since then there has been great progress in portland cement-based construction materials technologies brought about by advances in the materials science of composites and the development of chemical additives (admixtures) for applications. The resulting functionalities, together with its economy and the sheer abundance of its raw materials, have elevated ordinary portland cement (OPC) concrete to the status of most used synthetic material on Earth. While the 20th century was characterized by the emergence of computer technology, computational science and engineering, and instrumental analysis, the fundamental composition of portland cement has remained surprisingly constant. And, although our understanding of ordinary portland cement (OPC) chemistry has grown tremendously, the intermediate steps in hydration and the nature of calcium silicate hydrate (C-S-H), the major product of OPC hydration, remain clouded in uncertainty. Nonetheless, the century also witnessed great advances in the materials technology of cement despite the uncertain understanding of its most fundamental components. Unfortunately, OPC also has a tremendous consumption-based environmental impact, and concrete made from OPC has a poor strength-to-weight ratio. If these challenges are not addressed, the dominance of OPC could wane over the next 100 years. With this in mind, this paper envisions what the 21st century holds in store for OPC in terms of the driving forces that will shape our continued use of this material. Will a new material replace OPC, and concrete as we know it today, as the preeminent infrastructure construction material?
183 citations
Cites background from "18세기 의관 이수기(李壽祺)의 자기인식"
...Cements based on calcium sulfoaluminate compositions first appeared commercially in China in the 1970s(19), although references to such cements date back to the 1930s.(239) They are gaining relevance due to their ability to be made in a conventional rotary kiln using calcium, aluminum and sulfur-rich precursors....
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...20 However, the lower CO2 intensity comes at the cost of elevated SOx emissions, potentially elevated NOx emissions (due to the reduced processing temperatures), and a high-priced product (approximately two or three times more expensive than OPC) since the C$A precursors are more expensive than their OPC counterparts.(239) Compositionally, C$A clinkers contain Klein’s compound (ye’elemite, or C4A3$), ternesite (C5S2$) and belite (Ca2SiO4) Soluble sulfate, in the form of anhydrite, is added to regulate dimensional change and to ensure a period...
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TL;DR: A general variational approach to determine the steady state of open quantum lattice systems via a neural-network approach is presented and applied to the dissipative quantum transverse Ising model.
Abstract: We present a general variational approach to determine the steady state of open quantum lattice systems via a neural-network approach. The steady-state density matrix of the lattice system is constructed via a purified neural-network Ansatz in an extended Hilbert space with ancillary degrees of freedom. The variational minimization of cost functions associated to the master equation can be performed using a Markov chain Monte Carlo sampling. As a first application and proof of principle, we apply the method to the dissipative quantum transverse Ising model.
160 citations
TL;DR: This work obtains an analytical key rate formula for the loss-only scenario, confirming the square root scaling and also showing the loss limit, and simulates the key rate for realistic imperfections and shows that PM-MDI QKD can overcome the repeaterless bound with currently available technology.
Abstract: Variations of phase-matching measurement-device-independent quantum key distribution (PM-MDI QKD) protocols have been investigated before, but it was recently discovered that this type of protocol (under the name of twin-field QKD) can beat the linear scaling of the repeaterless bound on secret key capacity. We propose a variation of PM-MDI QKD protocol, which reduces the sifting cost and uses non-phase-randomized coherent states as test states. We provide a security proof in the infinite key limit. Our proof is conceptually simple and gives tight key rates. We obtain an analytical key rate formula for the loss-only scenario, confirming the square root scaling and also showing the loss limit. We simulate the key rate for realistic imperfections and show that PM-MDI QKD can overcome the repeaterless bound with currently available technology.
154 citations
Additional excerpts
...While values of pA, pB need to be optimized in the finite-key regime, in the infinite key limit, we can choose pA and pB arbitrarily close to 1 so that the sifting factor is asymptotically 1, like the efficient BB84 protocol [20]....
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TL;DR: In this paper, the authors proposed a scheme that uses phase-coherent optical signals and an auxiliary measuring station to distribute quantum information over significant channel losses, in excess of 90 dB.
Abstract: Quantum communications promise to revolutionise the way information is exchanged and protected. Unlike their classical counterpart, they are based on dim optical pulses that cannot be amplified by conventional optical repeaters. Consequently they are heavily impaired by propagation channel losses, which confine their transmission rate and range below a theoretical limit known as repeaterless secret key capacity. Overcoming this limit with today's technology was believed to be impossible until the recent proposal of a scheme that uses phase-coherent optical signals and an auxiliary measuring station to distribute quantum information. Here we experimentally demonstrate such a scheme for the first time and over significant channel losses, in excess of 90 dB. In the high loss regime, the resulting secure key rate exceeds the repeaterless secret key capacity, a result never achieved before. This represents a major step in promoting quantum communications as a dependable resource in today's world.
154 citations
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TL;DR: Chao Yuan-ling as mentioned in this paper, an associate professor in history at Middle Tennessee State University, studied medicine and society in late-imperial China, focusing on physicians in the city of Suzhou.
Abstract: (Chao Yuan-ling is currently associate professor in History at Middle Tennessee State University. She received her Ph.D. in History from UCLA in 1995. Her research is in the history of medicine in late imperial China. At present, she is working on a manuscript titled "Medicine and Society in Late Imperial China: A Study of Physicians in Suzhou.") * * *
12 citations