Single-photon generation and detection is at the forefront of modern optical physics research. This book is intended to provide a comprehensive overview of the current status of single-photon techniques and research methods in the spectral region from the visible to the infrared. The use of single photons, produced on demand with well-defined quantum properties, offers an unprecedented set of capabilities that are central to the new area of quantum information and are of revolutionary importance in areas that range from the traditional, such as high sensitivity detection for astronomy, remote sensing, and medical diagnostics, to the exotic, such as secretive surveillance and very long communication links for data transmission on interplanetary missions. The goal of this volume is to provide researchers with a comprehensive overview of the technology and techniques that are available to enable them to better design an experimental plan for its intended purpose. The book will be broken into chapters focused specifically on the development and capabilities of the available detectors and sources to allow a comparative understanding to be developed by the reader along with and idea of how the field is progressing and what can be expected in the near future. Along with this technology, we will include chapters devoted to the applications of this technology, which is in fact much of the driver for its development. This is set to become the go-to reference for this field. - Covers all the basic aspects needed to perform single-photon experiments and serves as the first reference to any newcomer who would like to produce an experimental design that incorporates the latest techniques - Provides a comprehensive overview of the current status of single-photon techniques and research methods in the spectral region from the visible to the infrared, thus giving broad background that should enable newcomers to the field to make rapid progress in gaining proficiency - Written by leading experts in the field, among which, the leading Editor is recognized as having laid down the roadmap, thus providing the reader with an authenticated and reliable source

Single-photon generation and detection is at the forefront of modern optical physics research. This book is intended to provide a comprehensive overview of the current status of single-photon techniques and research methods in the spectral region from the visible to the infrared. The use of single photons, produced on demand with well-defined quantum properties, offers an unprecedented set of capabilities that are central to the new area of quantum information and are of revolutionary importance in areas that range from the traditional, such as high sensitivity detection for astronomy, remote sensing, and medical diagnostics, to the exotic, such as secretive surveillance and very long communication links for data transmission on interplanetary missions. The goal of this volume is to provide researchers with a comprehensive overview of the technology and techniques that are available to enable them to better design an experimental plan for its intended purpose. The book will be broken into chapters focused specifically on the development and capabilities of the available detectors and sources to allow a comparative understanding to be developed by the reader along with and idea of how the field is progressing and what can be expected in the near future. Along with this technology, we will include chapters devoted to the applications of this technology, which is in fact much of the driver for its development. This is set to become the go-to reference for this field.

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.

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.

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.

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.

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.

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.