Experimental Methods in the Physical Sciences

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Latest release: November 29, 2013
Series
20
Books
Neutron Scattering – Fundamentals: Chapter 1. An Introduction to Neutron Scattering
Book 44·Nov 2013
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This introductory chapter provides a self-contained survey of the merits, strengths, and conceptual framework underpinning the use of neutrons as a probe of the structure and dynamics of materials. We also take the opportunity to illustrate important concepts using examples taken from the scientific literature, as well as establish the basic notation that will be used throughout, and listed in more detail in the List of Commonly Used Symbols.
Neutron Scattering – Fundamentals: Chapter 2. Neutron Sources
Book 44·Nov 2013
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This chapter reviews the most significant developments that have taken place in the design, construction, and operation of new neutron sources as well as the refurbishment programs of others already serving the neutron-scattering community. Such advances in neutron production devices are to be considered in conjunction with impressive achievements in the optimization of neutron delivery systems as well as in neutron instrumentation which overall resulted in a truly remarkable improvement in neutron count rates. As a result, the capabilities of experimental neutron sources are nowadays larger than ever before, despite there being fewer sources available. It is also worth remarking the coming into line of compact, accelerator-driven neutron sources as well as work carried out at small research reactors which, as exemplified during the past decade, have played an important role in helping the large, user-based facilities to carry out development work geared toward the achievement of full performance.
Neutron Scattering – Fundamentals: Chapter 3. Experimental Techniques
Book 44·Nov 2013
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In this chapter, neutron experimental techniques are described. The chapter covers the basics of neutron scattering, neutron source characteristics, diffraction techniques, inelastic neutron scattering, instruments for semi-macroscopic structure analysis, detectors, optics, choppers, and some concepts for instrument design. Techniques for both steady and pulsed sources are described, with more emphasis on the latter in view of the recent worldwide trend toward pulsed sources, generally pulsed spallation sources. The source character, even within the class of pulsed sources, has a significant influence on instrument design. Inelasticity effects in the total scattering technique are clearly specified in the chapter. Some details of chopper instruments, including resolution effects, are described, since this class of instruments has recently received considerable innovative development and use over a wide range of science. Recent developments in scintillation detectors are discussed as an alternative technology to more conventional 3He detectors. Optical components are becoming more and more important not only for neutron transport but also for background reduction. Neutron spin-echo techniques are presented as an example of the exploitation of polarized neutrons.
Neutron Scattering – Fundamentals: Chapter 4. Structure of Complex Materials
Book 44·Nov 2013
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Investigating the structure of a material is the first essential step in understanding its macroscopic properties. Getting insights of the interatomic and inter/intra-molecular interactions that influence the stability and the chemical behavior of a given compound allows its application in the best possible conditions and opens the way to design new materials with tailored properties. Neutron diffraction is a fundamental tool in structural characterization. Few examples concerning chemical crystallography, will be given to illustrate the properties that make neutrons the ideal probe for locating light atoms in the presence of heavy, electron-rich ones, and accurately determine atomic position and displacement parameters.
Neutron Scattering – Fundamentals: Chapter 5. Large-Scale Structures
Book 44·Nov 2013
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Large-scale structures encompass a broad area of science involving soft matter, biomaterials, and nanotechnology, defined by relatively weak interactions and length scales that extend from nanometer to micrometer. The key features of such systems that require characterization and quantification are surfaces and interfaces, adsorption, thin films, and self-assembly and hierarchical structures in solution and the solid phase. The neutron scattering techniques of neutron reflectivity and small-angle neutron scattering have emerged over the past two decades as important probes of these characteristic features of large-scale structures. In this chapter, the fundamentals of the two techniques are described in detail and the important experimental aspects summarized. Their application over a broad range of science is presented, in a way that highlights their unique properties and their important contribution to the field.
Neutron Scattering – Fundamentals: Chapter 6. Dynamics of Atoms and Molecules
Book 44·Nov 2013
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The aim of this chapter is to show how inelastic and quasielastic neutron scattering can be used to study dynamics in a range of materials varying from simple model systems to complex systems that are close to those used in technologically important applications. After a brief overview of the theoretical and instrumental concepts, we use examples to show how different types of atomic and molecular motions can be understood using neutron scattering experiments, frequently in combination with atomistic modeling methods. We cover aspects of physics, chemistry, biology, and materials science, but with the main focus on functional materials.
Single-Photon Generation and Detection: Chapter 1. Introduction
Book 45·Nov 2013
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Single-Photon Generation and Detection: Chapter 2. Photon Statistics, Measurements, and Measurements Tools
Book 45·Nov 2013
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To understand the nature of light sources, one needs to know the statistical properties of emitted light and how the tools used to measure those properties reflect those statistics. This chapter will cover the vocabulary and notation necessary for understanding the characteristics of the sources and detectors covered in this book. After a brief review of the quantized electric field and relevant operators, we explore properties of single-photon sources, starting with relationships among state vectors, density matrices and photon number probabilities . Next we investigate properties of , the second-order coherence, and how it relates to . We present an in-depth study of the Hanbury Brown-Twiss interferometer, showing how it can be used to accurately measure in many—but not all—experimental situations. This is followed by a discussion of bunching, antibunching, Poissonian photon statistics, high-order coherences and indistinguishability. The second half of the chapter discusses characteristics of single-photon detectors, starting with the definition of detection efficiency used in this book. We review the POVM (Positive-Operator-Valued-Measure) operators, use them to illustrate the distinction between photon number-resolving (PNR) detectors and click/ no-click detectors, and explore some of the practical limitations of photon number-resolving and energy-resolving detectors. We next discuss the time response of detectors, including timing latency, rise time, timing jitter, dead time, reset time and recovery time. Finally, we cover the distinction between dark count rate and background count rate, and briefly discuss afterpulse probability, active area and operating temperature.
Single-Photon Generation and Detection: Chapter 3. Photomultiplier Tubes
Book 45·Nov 2013
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We introduce the first photodetector that can be used to detect light at a single photon level. We review the technical demands for single photon detection and discuss how they it can be achieved by combining a photoelectronic effect and the effect of secondary emission. We also review typical components used in modern photoelectronic tubes.
Single-Photon Generation and Detection: Chapter 4. Semiconductor-Based Detectors
Book 45·Nov 2013
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This chapter presents a broad review of the principle, design, fabrication, operation, and performance of single-photon avalanche diodes (SPADs), and provides a comparative basis to assess the relative merits of the wide variety of devices and techniques covered. Particular attention is paid to the design of and operation of both silicon and high-speed-gated InGaAs/InP detection systems, as well as array-based systems.
Single-Photon Generation and Detection: Chapter 5. Novel Semiconductor Single-Photon Detectors
Book 45·Nov 2013
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In this Chapter, we summarize the current status and future prospects of a number of novel semiconductor-based single-photon detectors, including visible-light photon counters (VLPCs), solid-state photo-multipliers (SSPMs), and quantum-dot-based detectors. SSPMs and VLPCs utilize the gain produced by impact ionization of the impurity band to detect single photons over a wide wavelength range between 0.4 and 28. Quantum-dot-based single-photon detectors use photoconductive gain associated with photogenerated carriers trapped in quantum dots. We cover the basic operating principles of these devices, describe experimental results that demonstrate their unique attributes, present mathematical models that quantify their performance, and discuss the future of these novel detector technologies.
Single-Photon Generation and Detection: Chapter 6. Detectors Based on Superconductors
Book 45·Nov 2013
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Superconducting materials provide a unique opportunity for single-photon detectors. The combination of the strong non-linearity present in the superconducting-metal transition and in Josephson junctions; the unique electrical property of zero resistance; the fast relaxation processes present in many superconducting materials; and the easily engineered optical absorptance of metals results in a system that can be adapted to many photo-detection requirements. As a result of these material features, a variety of detector families have emerged in recent years based on superconducting nanowires, tunnel junctions, weak thermal links, and kinetic-inductive resonators. The detectors variously provide high speed single-photon detection; high-sensitivity in the infrared, optical, UV, or even x-ray wavelengths; and high efficiency. The resulting applications include quantum and classical high-data-rate communication, biological imaging, LIDAR, and VLSI circuit evaluation among others.
Single-Photon Generation and Detection: Chapter 7. Hybrid Detectors
Book 45·Nov 2013
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This chapter presents an overview of efforts to improve photon-counting detection systems through the use of hybrid detection techniques such as spatial- and time-multiplexing of conventional detectors, and frequency up-conversion. It reviews the basic operation for these methods and illustrates their utility in a number of applications showing new or improved capabilities compared with conventional methods.
Single-Photon Generation and Detection: Chapter 8. Single-Photon Detector Calibration
Book 45·Nov 2013
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We discuss applying single-photon detectors to measurements with high accuracy. Two primary standard methods of detector calibration are reviewed: one based on a radiant power measurement (substitution method) and the other—on a simultaneous generation of photon pairs (correlation method). It is shown how to apply these methods to two types of detectors: with no photon number resolution (PNR) and with full PNR. In addition, an experimental comparison of the two calibration methods with non-PNR detectors is presented.
Single-Photon Generation and Detection: Chapter 9. Quantum Detector Tomography
Book 45·Nov 2013
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As quantum detectors evolve to become ever more sophisticated, their description in terms of a limited number of generic parameters falls short. An alternative description of the performance of a detector is provided by its positive-operator-valued measure (POVM). In this chapter we introduce a technique, quantum detector tomography, which allows us to experimentally reconstruct the POVM of the detector under test. Detailed examples on how to apply this technique to phase-insensitive detectors are given. We also discuss the challenges for the tomography of phase-sensitive detectors and possible solutions.
Single-Photon Generation and Detection: Chapter 10. The First Single-Photon Sources
Book 45·Nov 2013
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Single-Photon Generation and Detection: Chapter 11. Parametric Down-Conversion
Book 45·Nov 2013
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In this chapter we review the process of parametric down-conversion (PDC) and discuss the different methods to use PDC as a heralded single-photon source. PDC is a non-linear optical process, where an incoming pump photon decays, under energy and momentum conservation, into a photon-pair. The creation of photons in pairs allows for the implementation of a single-photon source by detecting one photon (trigger) to herald the presence of its partner (signal). The engineering possibilities of PDC enable the generation of single-photons with high rates in a wide range of frequencies. This chapter is structured as follows: Section 11.2 describes the principles of PDC in non-linear media. We derive the quantum state of the generated photon-pairs, investigate the spectral purity and photon-number purity of the heralded signal photon and discuss the achievable single-photon generation rates. In section 11.3 we turn towards experimental realizations and introduce bulk crystal PDC. Section 11.4 elaborates on the use of periodic poling to engineer the PDC process. Finally, section 11.5 gives an overview over PDC in waveguides. A comparison of experimental data from various heralded singe-photon sources based on PDC is presented in section 11.6 with an overview of nonlinear materials suited for PDC given in section 11.7.
Single-Photon Generation and Detection: Chapter 12. Four-Wave Mixing in Single-Mode Optical Fibers
Book 45·Nov 2013
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The efficient generation of single photon and entangled photon states is of considerable interest both for fundamental studies of quantum mechanics and practical applications, such as quantum communications and computation. It is now well known that correlated pairs of photons suitable for such applications can be generated directly in a guided mode of an optical fiber through the nonlinear process of spontaneous four-wave mixing. Detection of one photon of the pair can be used to herald the presence of the other, in order to realise a probabilistic heralded single photon source. Alternatively, both photons can be used directly as an entangled photon pair if the source is designed such that the two photons are correlated in one or more of their degrees of freedom. This chapter provides an overview of the progress that has been made into the development of photon sources based on four-wave mixing in optical fibers. A theoretical model of four-wave mixing is described in Section 12.2, which demonstrates how the dispersion characteristics of an optical fiber influence the properties of the photon pair state that is generated. Section 12.3 focusses on heralded single photon sources operating in both the anomalous and normal dispersion regimes of optical fiber, and highlights several experimental demonstrations of this type of source. Section 12.4 discusses the concept of non-classical interference and the parameters of the generated photons that can influence the interference visibility. Section 12.5 expands upon this discussion to consider two different approaches for preparing photons in pure states that have been used to demonstrate high visibility two-photon interference. Section 12.6 describes several different experimental implementations of entangled photon pair sources. Finally, two practical applications using fiber-based photon sources are presented, with an all-fiber, quantum controlled-NOT gate discussed in Section 12.7, and the potential to use photonic fusion to build up large photonic cluster states outlined in Section 12.8.
Single-Photon Generation and Detection: Chapter 13. Single Emitters in Isolated Quantum Systems
Book 45·Nov 2013
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Single-Photon Generation and Detection: Chapter 14. Generation and Storage of Single Photons in Collectively Excited Atomic Ensembles
Book 45·Nov 2013
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We introduce the atomic-ensemble-based single-photon source. Thanks to the collective enhancement, It has the following advantages: it does not require strong coupling between light and matter, thanks to the collective enhancement; the generated narrow band single photons are storable, narrow-band, and highly controllable; and the single photons emitted from independent sources are pure and indistinguishable. In conjunction with a feedback circuit, the atomic-ensemble single-photon source can work in a deterministic way, where the production rate is significantly enhanced while low and good indistinguishability are preserved. The atomic-ensemble-based single-photon sources provide an essential tool for scalable quantum networks and linear-optical quantum computation.