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.
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.
Matter wave optics has a long tradition spanning over many decades starting with electron and ion optics. These techniques now find commercial applications in microscopy and lithography. Neutron optics contributed many beautiful experiments that tested many fundamental principles in quantum mechanics. Over the last decade the field of atom optics has been developed. In particular the availability of narrowband tunable laser sources has opened up the addressing of the internal electronic degrees of freedom of the atoms and as a result, the manipulation of their trajectories. The dissipative nature of the atom light interaction is used for laser cooling methods e.g. to collimate atomic beams to a high brightness whereas the dispersive nature of the interaction is used to realize different atom optical components like lenses, beam-splitters and mirrors. Consequently atom optics is now at a stage where applications of those elements in more complex systems are studied. An overview of recent developments is given. This includes atom interferometry and atom lithography experiments and experiments with a quasi 2D gas of ultra cold atoms in planar waveguides. Future directions and applications are outlined.
Abstract The past few decades have seen dramatic progress in our ability to manipulate and coherently control matter-waves. Although the duality between particles and waves has been well tested since de Broglie introduced the matter-wave analog of the optical wavelength in 1924, manipulating atoms with a level of coherence that enables one to use these properties for precision measurements has only become possible with our ability to produce atomic samples exhibiting temperatures of only a few millionths of a degree above absolute zero. Since the initial experiments a few decades ago, the field of atom optics has developed in many ways, with both fundamental and applied significance. The exquisite control of matter waves offers the prospect of a new generation of force sensors exhibiting unprecedented sensitivity and accuracy, for applications from navigation and geophysics to tests of general relativity. Thanks to the latest developments in this field, the first commercial products using this quantum technology are now available. In the future, our ability to create large coherent ensembles of atoms will allow us an even more precise control of the matter-wave and the ability to create highly entangled states for non-classical atom interferometry.
Atom Optics is a new branch of Atomic Physics, where one tries to act upon atoms, likewise one can act upon light (photons) in ordinary optics. The goal is therefore to reflect, focus, diffract, make interfere atoms1 .Afew years ago, this was considered as a fundamental goal, as had been the case decades ago for electron optics, or neutron optics. Indeed, it is always important to investigate the quantum behaviour of larger and larger objects, and studying the wave like behaviour of atoms has attracted a lot of attention. Moreover, atoms are objects that are coupled with the environment in a controlable way, in particular via quasi-resonant interaction with light. There is thus a hope to investigate how this coupling with the environment is relevant to the old problem of the division between the quantum world and the classical world2 ,and how it is related to the question of quantum decoherence. To keep in the domain of Atom Optics, the question of the preservation of coherence of the de Brogue waves describing the atomic motion is crucial. Another basic issue is the question of the collisions between atoms, or between an atom and a surface, when the atom is described as a matter-wave. From this point of view, the very interesting recent results in the domain of cold atoms collisions are only a part of what will probably come out, and new approaches may be fruitful. For instance, some collision effects may be considered as non-linear effects of atom optics... On the other hand, almost from the start, Atom Optics has been a domain where the question of applications has been raised. The experience of the many useful applications existing in the domain of electron and neutron optics has clearly shown the way. A first reason for expecting interesting applications to atom optics is the small value of the de Brogue wavelength, in the nanometer range or below, even at very low energies. This opens for instance the possibility of high resolution lithography, or of nanoprobes, at energies low enough to have a soft, non damaging interaction with a surface. Another important class of applications is in atomic interferometry. It can be shown that atomic interferometers (using atoms of mass Mat) are much more sensitive to inertial or gravitational effects3 than photonic interferometers (using photon of energy hw), by a ratio of the order of MatC2 / ho) . Note that this statement is true only under the condtion that the atomic and photonic interferometers under comparison have equivalent geometries, so that present day interferometers do not yet take full advantage of the 1011 factor of potential improvement. However, impressive results have already be demonstrated6. As a matter of fact, many of the papers presented in this symposium are linked to applications, either with atomic interferometers, or related to the possibility of deep focusing of an atomic beams. Most of these applications a Unite de recherche associée au CNRS can be easily understood by analogy with photon optics. However, there are also several features of atom optics that have no analogy in photon optics. The most important one is probably the possibility to increase the luminosity of an atomic beam (i.e. the flux of atoms per per unit time, surface, and solid angle) or —equivalently — to increase the atomic density in the phase space. This is possible by use of laser cooling, which is a dissipative process, and therefore is not constrained by the Liouville theorem. Another distinctive feature of atom optics —this one not particularly an advantage —is the lack of a sudden interface, that would be analogous to a glass-vacuum interface for light. By sudden interface, we mean that some characteristic parameter relevant to the propagation (the index of refraction in the case of light) changes on a scale small compared to the wavelength of the waves that propagate. In atom optics, the interfaces are usually soft, since the potentials acting on the atomic motion usually change on a scale large compared to the de Broglie wavelengths. In this overview, I intend to recall some basic principles of atom optics, and to point out some important analogies and differences with photon optics4 .Iexpect this discussion to be illustrated by the various presentations at this symposium, for which I hope to offer a framework. In addition, I will take the liberty to illustrate my presentation by some examples chosen among results obtained recently in my laboratory, on the subject of atomic mirrors. The comparison between atom optics and photon optics would of course be incomplete if I would not adress the question of the impact of Bose Einstein condensates onto Atom Optics. As many of us, I am convinced that we are assisting to a revolution as important for Atom Optics as the invention of the laser in the domain of Photon Optics, and we are lucky to have a full session on this hot subject.
Interference with atomic and molecular matter waves is a rich branch of atomic physics and quantum optics. It started with atom diffraction from crystal surfaces and the separated oscillatory fields technique used in atomic clocks. Atom interferometry is now reaching maturity as a powerful art with many applications in modern science. In this review the basic tools for coherent atom optics are described including diffraction by nanostructures and laser light, three-grating interferometers, and double wells on atom chips. Scientific advances in a broad range of fields that have resulted from the application of atom interferometers are reviewed. These are grouped in three categories: (i) fundamental quantum science, (ii) precision metrology, and (iii) atomic and molecular physics. Although some experiments with Bose-Einstein condensates are included, the focus of the review is on linear matter wave optics, i.e., phenomena where each single atom interferes with itself.
T hink about coherent systems, and odds are that the first example to cross your mind will be a laser: a device that emits monochromatic light homogenized so that the photons propagate with their phase in lockstep. The well-defined wavefront of the laser beam makes it possible to focus the light to spot sizes on the order of the wavelength of the light without the aberrations usually observed with the random wavefront of incoherent light. The well-defined phase also provides a medium capable of storing and carrying information more efficiently than the intensity-modulated signals typical of incoherent sources. These useful properties of coherence have made lasers almost ubiquitous in science and technology, and that “almost” is shrinking by the day.
In general, coherence comes about when individual components of a system act in unison, either in phase or with a fixed phase difference between the components. More accurately, the system can be described as a local oscillator whose wavefunction contains phase and amplitude terms that define how the system evolves in space and time. The collection of articles in this special issue describes the recent progress and developments of coherence in optical, atomic, and semiconductor systems, and how manipulating that coherence may lead to useful applications and to experimental systems for studying the elements of quantum mechanics.
Since the first demonstration of the laser in 1960, progress in improving the extent of the spatial and temporal coherence of laser light has been steady. Psaltis (p. [1359][1]) reviews developments in optical coherence and highlights examples of the key role coherence has played in applications in imaging, communication, and information processing and storage. Just as lasers revolutionized the field of optics, many researchers have high expectations that other coherent systems will provide similar advances in their respective fields. Exploiting the fundamental tenet of quantum mechanics whereby particles have the properties of waves, Kasevich (p. [1363][2]) reviews coherence effects in collections of cold atoms and describes how the shorter wavelengths associated with atoms and the recent accessibility of bright coherent atom sources may lead to precision measurements beyond anything currently available to the optical regime. For integration and potential applications, the ideal system would be based in semiconductors. Snoke (p. [1368][3]) describes recent work toward the formation of coherent semiconductor systems.
With coherence in the atomic and optical systems generally comprising macroscopic systems, Mabuchi and Doherty (p. [1372][4]) look at coherence effects at the quantum limit, probing the interactions between single atoms and single photons confined to high-quality cavities. In addition to providing invaluable information on the limits of quantum mechanics, such effects might also shed new light on information science in the quantum regime.
The section opens with a pair of News features by staff writers Charles Seife and Robert Service. Seife presents a smattering of common applications that scientists and engineers have found for coherent waves, whether in light, sound, or subatomic particles. Service describes efforts to create new coherent sources of the type of radiation known as “hard” x-rays—a long-sought range of high frequencies with enormous potential for scientific research, technology, and medicine.
[1]: /lookup/doi/10.1126/science.1078823
[2]: /lookup/doi/10.1126/science.1079430
[3]: /lookup/doi/10.1126/science.1078082
[4]: /lookup/doi/10.1126/science.1078446
This review discusses progress in the new field of coherent matter waves, in particular with respect to Bose-Einstein condensates. We give a short introduction to Bose-Einstein condensation and the theoretical description of the condensate wavefunction. We concentrate on the coherence properties of this new type of matter wave as a basis for fundamental physics and applications. The main part of this review treats various measurements and concepts in the physics with coherent matter waves. In particular we present phase manipulation methods, atom lasers, nonlinear atom optics, optical elements, interferometry and physics in optical lattices. We give an overview of the state of the art in the respective fields and discuss achievements and challenges for the future.