QUANTUM CRYPTOGRAPHY: Single Photons

Quantum cryptography offers the potential of totally secure transfer of information, but as Benjamin discusses in this Perspective, its practical implementation hinges on being able to generate single photons (rather than two or more) at a time. Michler et al. show how this condition can be met in a quantum dot microdisk structure. Single molecules were also recently shown to allow controlled single-photon emission.     

浅谈利用“Visual FoxPro”网络教学平台提高学生自主学习能力

网络教学作为现代信息技术与教学实践科学结合的一种新的教学形态，不仅从手段和形式上改变了传统教学，更从观念、过程、方法以及师生角色诸多层面赋予教学以新的含义。探讨了“Visual FoxPro”网络教学平台的开发与应用，进而分析了网络教学平台在教学过程中的优势以及学生自主学习能力的提高。     

QUANTUM COMPUTING: Quantum Entangled Bits Step Closer to IT

In contrast to today's computers, quantum computers and information technologies may in future be able to store and transmit information not only in the state "0" or "1," but also in superpositions of the two; information will then be stored and transmitted in entangled quantum states. Zeilinger discusses recent advances toward using this principle for quantum cryptography and highlights studies into the entanglement (or controlled superposition) of several photons, atoms, or ions.     

Probing quantum commutation rules by addition and subtraction of single photons to/from a light field

The possibility of arbitrarily "adding" and "subtracting" single photons to and from a light field may give access to a complete engineering of quantum states and to fundamental quantum phenomena. We experimentally implemented simple alternated sequences of photon creation and annihilation on a thermal field and used quantum tomography to verify the peculiar character of the resulting light states. In particular, as the final states depend on the order in which the two actions are performed, we directly observed the noncommutativity of the creation and annihilation operators, one of the cardinal concepts of quantum mechanics, at the basis of the quantum behavior of light. These results represent a step toward the full quantum control of a field and may provide new resources for quantum information protocols.     

Time and the quantum: erasing the past and impacting the future

The quantum eraser effect of Scully and Drühl dramatically underscores the difference between our classical conceptions of time and how quantum processes can unfold in time. Such eyebrow-raising features of time in quantum mechanics have been labeled "the fallacy of delayed choice and quantum eraser" on the one hand and described "as one of the most intriguing effects in quantum mechanics" on the other. In the present paper, we discuss how the availability or erasure of information generated in the past can affect how we interpret data in the present. The quantum eraser concept has been studied and extended in many different experiments and scenarios, for example, the entanglement quantum eraser, the kaon quantum eraser, and the use of quantum eraser entanglement to improve microscopic resolution.     

Looking to the future of quantum optics

Light has provided both fundamental phenomenology and enabling technology for scientific discovery for many years, and today it continues to play a central role in fundamental explorations and innovative applications. The ability to manipulate light beams and pulses with the quantum degrees of freedom of optical radiation will add to those advances. The future of quantum optics, which encompasses both the generation and manipulation of nonclassical radiation, as well as its interaction with matter, lies in the rich variety of quantum states that is now becoming feasible to prepare, together with the numerous applications in sensing, imaging, metrology, communications, and information processing that such states enable.     

Whither the future of controlling quantum phenomena?

This review puts into perspective the present state and prospects for controlling quantum phenomena in atoms and molecules. The topics considered include the nature of physical and chemical control objectives, the development of possible quantum control rules of thumb, the theoretical design of controls and their laboratory realization, quantum learning and feedback control in the laboratory, bulk media influences, and the ability to utilize coherent quantum manipulation as a means for extracting microscopic information. The preview of the field presented here suggests that important advances in the control of molecules and the capability of learning about molecular interactions may be reached through the application of emerging theoretical concepts and laboratory technologies.     

移动图书馆服务方式的比较与分析

随着科技的进步和时代的发展,结合移动互联网技术、WAP技术、数字图书馆技术的移动图书馆应用研究应运而生。论述了多种移动图书馆服务方式的理论概念及其应用,探讨智能手机操作系统在数字图书馆移动信息服务方式中的优势。     

Vacuum-induced transparency

Photons are excellent information carriers but normally pass through each other without consequence. Engineered interactions between photons would enable applications as varied as quantum information processing and simulation of condensed matter systems. Using an ensemble of cold atoms strongly coupled to an optical cavity, we found that the transmission of light through a medium may be controlled with few photons and even by the electromagnetic vacuum field. The vacuum induces a group delay of 25 nanoseconds on the input optical pulse, corresponding to a light velocity of 1600 meters per second, and a transparency of 40% that increases to 80% when the cavity is filled with 10 photons. This strongly nonlinear effect provides prospects for advanced quantum devices such as photon number-state filters.     

网络环境下信息资源共享模式研究

本文介绍了网格技术、Web服务、P2P技术和Z39.50协议的内涵及特点,论述了基于四种技术的信息资源共享的模式的基本原理,并对四种信息资源共享模式进行了比较分析.     

Condensed matter physicists shrink their horizons

In the world of the condensed matter physicist, a micron is a chasm and a millimeter an ocean. At the March American Physical Society meeting in Seattle, some of the 4500 physicists probed the hazards of the micro world, where weird quantum effects can scramble information. Others outlined its opportunities: Molecular engineering that is leading to new information storage materials, and minute structures that could form tethers and containers in some future nanotechnology.     

Understanding molecular dynamics quantum-state by quantum-state

It is now possible to resolve completely the initial and final quantum states in chemical processes. Spectra of reactive intermediates, of highly vibrationally excited molecules, and even of molecules in the process of falling apart have been recorded. This information has led to greater understanding of the molecular structure and dynamics of small gas-phase molecules. Many of the concepts and spectroscopic techniques that have been developed will be valuable throughout chemistry.     

Coherent control of decoherence

Manipulation of quantum interference requires that the system under control remains coherent, avoiding (or at least postponing) the phase randomization that can ensue from coupling to an uncontrolled environment. We show that closed-loop coherent control can be used to mitigate the rate of quantum dephasing in a gas-phase ensemble of potassium dimers (K2), which acts as a model system for testing the general concepts of controlling decoherence. Specifically, we adaptively shaped the light pulse used to prepare a vibrational wave packet in electronically excited K2, with the amplitude of quantum beats in the fluorescence signal used as an easily measured surrogate for the purpose of optimizing coherence. The optimal pulse increased the beat amplitude from below the noise level to well above it, and thereby increased the coherence life time as compared with the beats produced by a transform-limited pulse. Closed-loop methods can thus effectively identify states that are robust against dephasing without any previous information about the system-environment interaction.     

农业院校图书馆为"三农"服务的探索与思考

本文就农业院校图书馆应如何利用自身优势 ,更深层次地开发农业信息 ,并结合自身工作实践 ,谈了谈为“三农”服务的体会。     

基于ERDASIMAGINE的图像投影方法探讨

介绍地图投影相关概念，论述如何在ERDASIMAGINE软件平台下实现图像的投影变换、解决不同坐标基准影像数据的共享、方便多源GIS数据集成。     

知识管理与图书馆可持续发展

介绍了知识管理和可持续发展的概念,分析了图书馆知识管理和可持续发展的内容,以及它们之间的相互关系,提出进行知识管理是实现图书馆可持续发展的有效途径,并就如何增强图书馆的核心竞争力、推动图书馆的持续发展,给出了一些加强图书馆知识管理的相应措施.     

INFORMATION THEORY: 'Ultimate PC' Would Be a Hot Little Number

A physicist has used the laws of thermodynamics, information, relativity, and quantum mechanics to figure out the ultimate physical limits on the speed of a computer. His calculations show that, in principle, a kilogram of matter in a liter-sized container could be an "ultimate laptop" more than a trillion trillion trillion times as powerful as today's fastest supercomputer--if it could be turned into a black hole.     

五常法在图书馆管理中的应用

日本企业依靠“五常法”打造出众多世界名牌，图书馆管理也应吸取其精华，强化服务意识，提升服务档次。本文就“五常法”在图书馆工作中的具体运用及运用中应注意的问题进行了简要阐述。     

"数字地球"与"数字农业"

“数字地球”就是信息化的地球，它包括全部地球资料的数字化、网络化、智能化和可视化的过程在内。数字地球的核心思想是用数字化手段整体性地解决地球问题并最大限度地利用信息资源。“数字农业”是实施“数字地球”战略的重要组成部分。本文分别论述了“数字地球”、“数字农业”的源起、概念、内涵、特点及中国的发展战略。