Slow light has received growing interest since 1999 when the propagation velocity of light was reduced in an experiment to 17 m/s, i.e. almost 20 million times slower than in vacuum. Two years later light pulses were stopped, or more specifically stored in an atomic medium and subsequently released after some time. This provided the basis for important applications in photon-based quantum information technology. The present chapter explains what slow light is and what it is good for, how to understand the physics of it and how one can practically make light go so slow. To answer these questions, the chapter uses simple pictures, on the one hand, and supplements them with a little bit of details, on the other hand, for those who want to go slightly deeper into the field. The chapter also discusses more recent generalizations of slow light, such as stationary and spinor slow light which are interesting model system and can be used to understand more complex quantum systems. These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
Slow light has received growing interest since 1999 when the propagation velocity of light was reduced in an experiment to 17 m/s, i.e. almost 20 million times slower than in vacuum. Two years later light pulses were stopped, or more specifically stored in an atomic medium and subsequently released after some time. This provided the basis for important applications in photon-based quantum information technology. The present chapter explains what slow light is and what it is good for, how to understand the physics of it and how one can practically make light go so slow. To answer these questions, the chapter uses simple pictures, on the one hand, and supplements them with a little bit of details, on the other hand, for those who want to go slightly deeper into the field. The chapter also discusses more recent generalizations of slow light, such as stationary and spinor slow light which are interesting model system and can be used to understand more complex quantum systems. These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
I n 1998, laser pulses were slowed [1] in a Bose-Einstein condensate (BEe) [2] ofsodium to only 17 m/s, more than seven orders of magnitude lower than the speed of light in vacuum. Associated with the dramatic reduction factor for the light speed was a spatial compression of the pulses by the same large factor. A light pulse, which was more than 1 km long in vacuum, was compressed to a size of -50 flm, and at that point was completely contained within the condensate [1]. This allowed the light-slowing experiments to be brought to their ultimate extreme [3]: in the summer of 2000, light pulses were completely stopped, stored, and subsequently revived in an atomic medium, with millisecond storage times [4]. The initial ultra-slow light experiments spurred a flurry of slow light investigations, and slow or partially stopped light has now been observed in limited geometries in warm rubidium vapours [5-7], liquid-nitrogen cooled crystals [8], and recently in room temperature crystals [9]. Here, we begin with a discussion ofultra-slow and stopped light. We describe how cold atoms and Bose-Einstein condensates have been manipulated to generate media with extreme optical properties. While the initial experiments concentrated on the light propagation, we have recently begun a number of investigations of the effects that slow light has on the medium in which it propagates. Effects are profound because both the velocity and length scales associated with propagating light pulses have been brought down to match the characteristic velocity and length scales of the medium. With the most recent extension, the light roadblock [10], we have compressed light pulses to a length ofonly 2 f!ill. Here, we describe the use of ultra-compressed light pulses to probe superfluidity and the creation of quantized vortices in BEes through formation of'superfluid shock. waves'. We also present the observation of an ultra-slow-light-based, pulsed atom laser. Furthermore, we demonstrate the use of slow and stopped light for manipulation of optical information, in particular in Bose-Einstein condensates that allow for phase coherent processing of three-dimensional, compressed patterns of stored optical information.
In the framework of the nonlinear Λ model, propagation of solitons was analysed in atomic vapours and Bose-Einstein condensates. The complicated nonlinear interplay between fast and slow-light solitons in a Λ-type medium was shown to facilitate control of its optical transparency and formation of optical gates. An exact analytical description was given for the deceleration, stopping and revival of slow-light solitons in the experimentally relevant non-adiabatic regime. A stopping slow-light soliton imprints a localized immobile polarization pattern in the medium, which, as explicitly demonstrated here, can be used as a bit of readable optical memory. The whole process can be controlled with the background field and an auxiliary laser field. The latter regulates the signal velocity, while the slow-light soliton can be stopped by switching off the former. The location and shape of the imprinted memory bit were also determined. With few assumptions characteristic of slow light, the Λ model was reduced to a simpler nonlinear model that also describes two-dimensional dilatonic gravity. Exact solutions could now be derived also in the presence of relaxation. Spontaneous decay of the upper atomic level was found to be strongly suppressed, and the spatial form of the decelerating slow-light soliton was preserved, even if the optical relaxation time was much shorter than the typical time scale of the soliton. The effective relaxation coefficient of the slow-light soliton was significantly smaller than that of an arbitrary optical pulse. Such features are obviously of great importance when this kind of system is applied, in practice, to information processing. A number of experimentally observable properties of the solutions reported were found to be in good agreement with recent experimental results, and a few suggestions are also made for future experiments.
Fast or slow light propagation means that the group velocity of a quasi-monochromatic light pulse propagating in a resonant medium can be significantly faster or slower than the light speed in a vacuum. Since the end of the last century and the beginning of this century, studies on this subject have attracted a great deal of interest. Remarkable progress has been achieved, based on various nonlinear optical interactions in resonant media. The fundamental research on this subject can enrich our understanding of special relativity and causality in physics. On the other hand, those mechanisms and techniques developed for fast and slow light propagation have provided the potential for many future applications, such as optical buffers and variable delay lines for optical networks, optical computing, optical telecommunications, optical data storage, and signal processing.
The propagation of light in dispersive media is a subject of fundamental as well as practical importance. In recent years attention has focused in particular on how refractive index can vary with frequency in such a way that the group velocities of optical pulses can be much greater or much smaller than the speed of light in vacuum, or in which the refractive index can be negative. Treating these topics at an introductory to intermediate level, Fast Light, Slow Light and Left-Handed Light focuses on the basic theory and describes the significant experimental progress made during the past decade. The book pays considerable attention to the fact that superluminal group velocities are not in conflict with special relativity and to the role of quantum effects in preventing superluminal communication and violations of Einstein causality. It also explores some of the basic physics at the opposite extreme of very slow group velocities as well as stopped and regenerated light, including the concepts of electromagnetically induced transparency and dark-state polaritons. Another very active aspect of the subject discussed concerns the possibility of designing metamaterials in which the refractive index can be negative and propagating light is left-handed in the sense that the phase and group velocities are in opposite directions. The last two chapters are an introduction to some of the basic theory and consequences of negative refractive index, with emphasis on the seminal work carried out since 2000. The possibility that "perfect" lenses can be made from negative-index metamaterials-which has been perhaps the most controversial aspect of the field-is introduced and discussed in some detail.
The propagation of light in dispersive media is a subject of fundamental as well as practical importance. In recent years attention has focused in particular on how refractive index can vary with frequency in such a way that the group velocities of optical pulses can be much greater or much smaller than the speed of light in vacuum, or in which the refractive index can be negative. Treating these topics at an introductory to intermediate level, Fast Light, Slow Light and Left-Handed Light focuses on the basic theory and describes the significant experimental progress made during the past decade. The book pays considerable attention to the fact that superluminal group velocities are not in conflict with special relativity and to the role of quantum effects in preventing superluminal communication and violations of Einstein causality. It also explores some of the basic physics at the opposite extreme of very slow group velocities as well as stopped and regenerated light, including the concepts of electromagnetically induced transparency and dark-state polaritons. Another very active aspect of the subject discussed concerns the possibility of designing metamaterials in which the refractive index can be negative and propagating light is left-handed in the sense that the phase and group velocities are in opposite directions. The last two chapters are an introduction to some of the basic theory and consequences of negative refractive index, with emphasis on the seminal work carried out since 2000. The possibility that "perfect" lenses can be made from negative-index metamaterials-which has been perhaps the most controversial aspect of the field-is introduced and discussed in some detail.
Abstract When ensembles of atoms interact with coherent light fields, a great many interesting and useful effects can be observed. In particular, the group velocity of the coherent fields can be modified dramatically. Electromagnetically induced transparency is perhaps the best known example, giving rise to very slow light. Careful tuning of the optical fields can also produce stored light where a light field is mapped completely into a coherence of the atomic ensemble. In contrast to stored light, in which the optical field is extinguished, stationary light is a bright field of light with a group velocity of zero. Stationary light has applications in situations where it is important to maintain an optical field, such as attempts to engineer large nonlinear interactions. In this paper, the stationary light demonstrations published to date are reviewed and a unified theoretical framework that describes the experimental observations is provided. Possible applications of stationary light are also discussed, with a particular focus on all‐optical phase gates for quantum information technology.