Among all the inventions that quantum physics has produced, the laser holds a particularly important place, both for the rich story of successive discoveries that led to its birth, and for the role it has played in fundamental and applied research. I recall here the lineage of theoretical discoveries and experiments that have marked this history, restricting myself to the contribution of lasers to blue sky science and leaving apart its well-known role in various domains of technology. This story started from advances in the old quantum theory, from Einstein’s theoretical description of stimulated emission to O. Stern’s experimental discovery of the spatial quantization of the electron spin. Nuclear magnetic resonance, atomic clocks, optical pumping, and masers followed and the pace of discoveries accelerated with the appearance of the laser in 1960. This extraordinary light source has since enabled breakthroughs in fundamental physics and opened up fields of research that could not even have been imagined at the time of its birth. I was fortunate to begin my career in physics at this crossroad of atomic physics and optics. I give in this article my personal view of the great adventures in fundamental research in which I participated as an actor or spectator, from the cooling and trapping of atoms by light, to the physics of quantum gases of bosons and fermions, the manipulation of individual quantum particles and quantum simulations. Many other areas of fundamental physics, which I will only mention briefly, owe their development to lasers and further advances are still to be expected in the years to come.
Among all the inventions that quantum physics has produced, the laser holds a particularly important place, both for the rich story of successive discoveries that led to its birth, and for the role it has played in fundamental and applied research. I recall here the lineage of theoretical discoveries and experiments that have marked this history, restricting myself to the contribution of lasers to blue sky science and leaving apart its well-known role in various domains of technology. This story started from advances in the old quantum theory, from Einstein’s theoretical description of stimulated emission to O. Stern’s experimental discovery of the spatial quantization of the electron spin. Nuclear magnetic resonance, atomic clocks, optical pumping, and masers followed and the pace of discoveries accelerated with the appearance of the laser in 1960. This extraordinary light source has since enabled breakthroughs in fundamental physics and opened up fields of research that could not even have been imagined at the time of its birth. I was fortunate to begin my career in physics at this crossroad of atomic physics and optics. I give in this article my personal view of the great adventures in fundamental research in which I participated as an actor or spectator, from the cooling and trapping of atoms by light, to the physics of quantum gases of bosons and fermions, the manipulation of individual quantum particles and quantum simulations. Many other areas of fundamental physics, which I will only mention briefly, owe their development to lasers and further advances are still to be expected in the years to come.
Quantum many-body systems, as they appear in different branches of physics and chemistry, are very hard to simulate. The number of parameters defining their quantum states grows exponentially with the number of constituents. This prevents us from exploring and investigating relevant problems involving relatively small numbers of subsystems even with the help of the most powerful supercomputers. Richard Feynman already noticed this difficulty back in 1981 when he wrote his visionary paper “Simulating Physics with Computers” [Int. J. Theor. Phys. 21:6/7, 467 (1982)]. There, he proposed to use quantum systems (as opposed to classical computers) to perform the simulation and in this way to circumvent the need to store and compute a colossal number of parameters, necessary to describe the pertaining superpositions. What was a visionary idea at that time has become a very active field of research in the last few years. The extraordinary progress of both theoretical and experimental research in quantum physics allows us now to tame, control, and manipulate various quantum systems with unprecedented precision. Laser, magnetic, electronic and other technologies enable us to arrange quantum subsystems in different geometries, modify their interactions, and detect them. This allows us to engineer Hamiltonians and emulate systems displaying some of the most intriguing quantum phenomena. This tremendous progress is, to a large extent, due to the pioneering work of many researchers during the last twenty to thirty years. Here, the investigations of basic phenomena with one or few atoms or photons were of particular impact. The degree of control achieved in the experiments has enabled the observation of mind-boggling quantum effects, related to the superposition principle or to entangled states, and their disappearance due to decoherence. In fact, the 2012 Nobel Prize has been awarded to two scientists, S. Haroche and D. Wineland, for such ground-breaking experiments. Such experiments, often in combination with laser cooling of atoms or ions and Bose-Einstein condensation, have formed one of the pillars on which the field of quantum simulations is being established. Quantum simulations with cold atoms, either in magnetic traps or in optical lattices, with trapped ions, with photons, with superconducting devices, with quantum dots, etc., have been theoretically proposed and experimentally considered by many researchers. Most of the proposals so far deal with problems in condensed matter physics that are either difficult to tackle with modern supercomputers or are difficult to observe in solid state systems. This has established a very close link between different disciplines, like atomic, molecular, and optical (AMO) physics, and condensed matter physics. Although some of the experiments are still in their infancy, and a lot of research is still needed, the extraordinary progress made in all these research areas during the last few years makes us feel confident that in the not too distant future quantum simulators will provide a key tool to investigate many-body quantum systems. Furthermore, we also expect that quantum simulators will help quantum physicists to establish new and fruitful links to other scientific communities, like high-energy physics or quantum chemistry. The present special issue contains various review papers as well as research papers on quantum simulations. It starts out with two papers written by last year's Nobel Prize winners describing their foundational work (Wineland, p. 739 and Haroche, p. 763). The issue continues with three thorough, invited review papers covering different topics on quantum simulations. The first one reviews recent theoretical proposals to use cold atoms in optical lattices to simulate lattice gauge theories of the sort that appear in high-energy physics (U.-J. Wiese, p. 783). The second covers both theoretical proposals and experimental demonstrations of cold-atom systems to simulate the physics of matter in the presence of gauge fields, displaying so-called topological phenomena, which so far have only been observed in solid-state systems (I. Spielman, p. 794). The third one contains an extensive overview and new proposals to perform a broad range of quantum simulations using quantum dot systems (P. Barthelmy et al., p. 813). The issue also includes six original papers with a variety of theoretical proposals as well as the introduction of novel theoretical techniques related to the field of quantum simulation. The field of quantum simulations is just starting, but we are confident that it will soon generate an even larger plethora of new ideas and discoveries, trigger interdisciplinary research, and lead us to the adventure of describing and understanding the quantum world. We hope that this special issue will help future researchers in such an exciting adventure. Rainer Blatt received his PhD degree in physics from the University of Mainz in 1981. As a postdoctoral fellow he worked on atomic beam cooling in Boulder, CO and later as a research assistant in Hamburg with single trapped ions. In 1995 he accepted a chair in experimental physics at the University of Innsbruck working on quantum information processing with trapped ions. Since 2003 he is also scientific director at the Institute for Quantum Optics and Quantum Information (IQOQI) of the Austrian Academy of Sciences. Immanuel Bloch received his PhD degree in physics from the Ludwig Maximilians University of Munich in 2000. As a junior group leader, he continued in Munich starting his work on ultracold quantum gases in optical lattices. In 2008 he was appointed scientific director of the newly founded division on Quantum Many-Body Systems at the Max Planck Institute of Quantum Optics. Since 2009 he also holds a chair in quantum optics at the Ludwig-Maximilians University of Munich. Ignacio Cirac received his PhD degree in physics from the Universidad Complutense de Madrid in 1991. He was professor at the Universities of Castilla-La Mancha and Innsbruck from 1991–1996 and 1996–2001, respectively. In 2001 he joined the Max-Planck Institute of Quantum Optics, where he leads the Theory Division. His current research interests include quantum information theory and quantum optics. Peter Zoller obtained his doctorate from the University of Innsbruck in 1977. He was Max Kade Fellow at the University of Southern California from 1978/79, and was JILA visiting Fellow 1981/82 and 1988. In 1990 he became JILA Fellow and professor of physics at the University of Colorado. At the end of 1994, he accepted a chair at the University of Innsbruck, where he has worked ever since. Since 2003, he has also held the position of Scientific Director at the Institute for Quantum Optics and Quantum Information (IQOQI) of the Austrian Academy of Sciences.
When the Nobel Prize for Physics was awarded to Claude Cohen-Tannoudji, William D. Philipps and Steven Chu in 1997 for the development of methods for cooling and trapping atoms using lasers, this was the reward for two decades of investigations not only touching upon the fundamental aspects of the light–matter interaction, but also leading to a range of applications. On the theoretical level, the advent of this field of research in the late 1970s stimulated the development of various theoretical methods for describing the radiative forces by which light affects the motion of atoms. On the experimental level, judicious use of the radiative forces exerted by lasers made it possible to obtain a drastic reduction of atomic velocities – in other words, to cool an atomic vapour. These advances were characterized by a remarkable cross-fertilization of theoretical and experimental innovations. It was not long before applications began to appear in the field of high-resolution spectroscopy, since ultracold, i.e. slow, atoms can be observed for longer periods, and this allows greater accuracy when measuring atomic resonance frequencies than could be obtained for atoms at room temperature. Based on such resonances, the most accurate clocks in the world use laser-cooled atoms or ions. Atom interferometry is another application of laser manipulation of atoms, which can be applied to measure inertial effects, due for example to the rotation of the Earth or the motion of a vehicle, with an accuracy that already exceeds traditional methods.
Abstract The invention and development of laser methods for cooling and trapping atoms have led to the advent of the physics of ultracold matter. Low-temperature quantum physics has so far dealt with condensed media, wherein quantum phenomena (superfluidity and superconductivity) usually manifest themselves at temperatures of a few kelvin. Laser cooling and trapping of atoms have made it possible to successively attain millikelvin, microkelvin, and nanokelvin temperatures, at which the de Broglie wavelength of the atoms becomes commensurable with the interatomic separation, even in dilute gases. The interaction of atoms in ultracold dilute gases becomes essentially quantum mechanical. The physics of such quantum gases is more akin to the well-developed physics of condensed matter at low temperatures. It is in essence a boundary field between atomic, laser, and condensed-matter physics. Following the first, pioneering experiments on the Bose–Einstein condensation of alkali-metal atoms, this field has continued to develop at a very fast pace, which can be explained by the vast variety of particles (atoms, isotopes, and molecules) that can be laser cooled and trapped under degeneracy conditions. This is much more than physicists had at their disposal previously (3,4He). Moreover, laser radiation and magnetic fields additionally make it possible to control not only the intrinsic quantum state of the interacting ultracold particle species, but also the interaction of the particles. All this makes the research in the field of quantum gases a great breakthrough, both in atomic–molecular physics and in many-body-interaction physics, which heretofore was the prerogative of low-temperature condensed-matter physics.
More than a century after the beginning of the quantum revolution, historians continue to explore new facets in the history of quantum physics, and to re-examine some of its better-known aspects. The thirteen papers collected in this volume, by authors from five continents, present central trends in the current study of quantum physics within its theoretical, experimental, philosophical, technological and social contexts. They discuss developments from the late nineteenth to the early twenty-first century and go beyond the traditional focus on Europe and North America to include China and Japan, and beyond the Heisenbergs and Diracs to reveal the role of actors who hitherto have played only a marginal role in historical account, but left their mark on the development of quantum physics. Also a wider array of subdisciplines comes into view, from optics to quantum gravity through quantum electrodynamics, from atomic and nuclear to condense matter physics and foundations of physics. Moreover, the volume shows that fields such as dispersion, physical chemistry and solid state physics should not be seen merely as areas of applications of ideas that evolved in other contexts, but should be regarded as birthplaces of important theoretical insights. The perspective of the papers ranges from local histories to global discussions, from conceptual changes via the role of experimentation to interactions with social and technological forces and to the interpretation of the theory.
Atomic, molecular and optical physics is a field which, during the last few decades, has known spectacular developments in various directions, like nonlinear optics, laser cooling and trapping, quantum degenerate gases, quantum information. Atom–photon interactions play an essential role in these developments. This book presents an introduction to quantum optics which, I am sure, will provide an invaluable help to the students, researchers and engineers who are beginning to work in these fields and who want to become familiar with the basic concepts underlying electromagnetic interactions. Most books dealing with these subjects follow either a semi-classical approach, where the field is treated as a classical field interacting with quantum particles, or a full quantum approach where both systems are quantized. The first approach is often oversimplified and fails to describe correctly new situations that can now be investigated with the development of sophisticated experimental techniques. The second approach is often too difficult for beginners and lacks simple physical pictures, very useful for an initial understanding of a physical phenomenon. The advantage of this book is that it gives both approaches, starting with the first, illustrated by several simple examples, and introducing progressively the second, clearly showing why it is essential for the understanding of certain phenomena. The authors also clearly demonstrate, in the case of non-linear optics and laser cooling, how advantageous it may be to combine both approaches in the analysis of an experimental situation and how one can get from each point of view useful, complementary physical insights.
Our ability to manipulate the coherence properties of light has been at the heart of many of the most important scientific and technological innovations of this century. There can hardly be a home in this country that does not possess a laser in the form of a compact disc player or a CDROM. When we talk on the phone, or send messages on the Internet, there is a high probability that our message will be encoded by a laser into pulses of light to be passed through optical fibres. In the last few years physicists have been discovering that it is possible to control the coherence properties of atoms, and are now developing tools analogous to those which have been developed to take advantage of the coherence properties of light. In the next decade we can look forward to seeing the application of lasers, fibres, mirrors and waveguides for atoms. Already we have been able to construct interferometry experiments using beams of atoms and these have proved to be extremely sensitive measurement devices, allowing us to test physical theories and measure fundamental constants to a level of precision not previously possible. Will these developing technologies ever be as ubiquitous as their optical forebears? In this paper we discuss the anticipated uses of this technology for both fundamental science and industrial applications. Starting from an explanation of the meaning of coherence and a comparison of the properties of photons and atoms, we describe the development of the science of atom optics. The tortuous route towards the great achievement of producing a Bose–Einstein condensate is described, and we explain why this is the most important step towards a laser–like source of atoms. Numerous other optical elements for atoms have been built or are on the drawing board, and we describe how these may be used to manipulate atoms with a precision that has never before been achieved, and look ahead to what we can learn about physics using these tools and at how they can be put to practical use.