Atom optics with microfabricated optical elements

Atom optics, guided atoms, and atom interferometry

Atom optics is the coherent manipulation of the atomic matter waves originally postulated by the developers of quantum mechanics. These pioneers also proposed the use of stimulated light forces to manipulate particles. These ideas have been combined with current technology to produce the field of atom optics. This, in turn, has shed new light on old quantum problems like the which way problem and the origins of quantum decoherence. Bose Einstein condensates combine naturally with atom optics to produce new results such as the coherent amplification of matter waves. This review of atom optics traces these connections.

Recent developments in atom optics have led to different approaches to lithographic techniques with neutral atoms. One of these is the use of diffraction from free-standing masks, which is sometimes called atom holography. There, narrow structures arise due to matter-wave interference in the Fresnel regime. In the presented experiment, we demonstrate that the wave nature of atoms can be used to produce periodic structures with small periodicities. We used the Talbot effect in the Fresnel diffraction regime behind a microfabricated transmission grating. The Talbot effect is the self-imaging of a grating of periodicity d illuminated with plane coherent waves.

We describe a method for sensing short range forces using matter wave interference in dielectric nanospheres. When compared with atom interferometers, the larger mass of the nanosphere results in reduced wave packet expansion, enabling investigations of forces nearer to surfaces in a free-fall interferometer. By laser cooling a nanosphere to the ground state of an optical potential and releasing it by turning off the optical trap, acceleration sensing at the $10^{-8}$m/s$^2$ level is possible. The approach can yield improved sensitivity to Yukawa-type deviations from Newtonian gravity at the $5$ $\mu$m length scale by a factor of $10^4$ over current limits.

Recent progress in atom optics has culminated in several demonstrations of atom interferometers. These rely on the passage of atoms through mechanical or light gratings and may be roughly characterized as Mach–Zehnder interferometers. In this communication, we propose a scheme to realize a Fabry–Perot interferometer for atoms. The mirrors are realized by the field gradient resulting from the spatial mode structure in optical or microwave cavities. When ultra- cold atoms impinge on such cavities, they experience quantum mechanical reflection and transmission that result in the appearance of longitudinal modes for the atomic wave function. We present a model of such a Fabry–Perot interferometer for two-level atoms. We discuss the intra-cavity matter–wave mode structure as well as the transmittivity and reflectivity characteristics of the interferometer. The potential generation of macroscopic quantum waves using such a device, as well as its potential as a sensitive photon detector, will be addressed.

Atomic matter waves, like electromagnetic waves, can be focused, reflected, guided and split by currently available passive atom-optical elements. However, the key for many applications of electromagnetic waves lies in the availability of amplifiers. These active devices allow small signals to be detected, and led to the development of masers and lasers. Although coherent atomic beams have been produced1,2,3,4, matter wave amplification has not been directly observed. Here we report the observation of phase-coherent amplification of atomic matter waves. The active medium is a Bose–Einstein condensate, pumped by light that is far off resonance. An atomic wave packet is split off the condensate by diffraction from an optical standing wave, and then amplified. We verified the phase coherence of the amplifier by observing interference of the output wave with a reference wave packet. This development provides a new tool for atom optics and atom interferometry, and opens the way to the construction of active matter-wave devices.

We review the field of atom interferometer inertial sensors. We begin by reviewing the path integral formulation of atom interferometers and then specialize the treatment to light-pulse atom interferometers and, in particular, gravimeters and gyroscopes. The bulk of the article focuses on the most common type of atom interferometer – the light-pulse interferometer, where the atom optics are composed of light pulses. Our article mainly focuses on a review of advances that aid in the practical implementation of atom interferometers toward gravimetry and inertial navigation. To that end, we develop a navigation model that aids in the connection of parameters and performance of atom interferometers to actual quantities of interest to the navigation community. Practical considerations of atomic inertial sensors, including dynamic range, bandwidth, dead time, and cross-coupling effects are discussed, before we review the field of accelerometer and gyroscope atom interferometers. Finally, we review advances in trapped-atom interferometers.

Atom optics demonstrates optical phenomena with coherent matter waves, providing a foundational connection between light and matter. Significant advances in optics have followed the realization of structured light fields hosting complex singularities and topologically non-trivial characteristics. However, analogous studies are still in their infancy in the field of atom optics. Here, we investigate and experimentally create knotted quantum wavefunctions in spinor Bose–Einstein condensates which display non-trivial topologies. In our work we construct coordinated orbital and spin rotations of the atomic wavefunction, engineering a variety of discrete symmetries in the combined spin and orbital degrees of freedom. The structured wavefunctions that we create map to the surface of a torus to form torus knots, Möbius strips, and a twice-linked Solomon’s knot. In this paper we demonstrate close connections between the symmetries and underlying topologies of multicomponent atomic systems and of vector optical fields—a realization of topological atom-optics.

By utilizing the wave nature of atoms, one can devise a variety of atom-based devices and systems in analogy with optical versions. Integrated atom optics seeks to do for atom optics what integration has done for photon-optics, namely to miniaturize and turn atom optics into a practical technology. Already a variety of atom optical waveguides and beamsplitters have been demonstrated in research labs and now attention is turning towards the integration of coherent atom sources, that is, Bose-Einstein condensates, directly onto atom "chips." We describe some of most recent work in integrated atom optics and some of our own efforts to miniaturize atom optics systems with the help of MEMS technology.

Optics and Interferometry with Atoms and Molecules

We report on measurements of splitting Bose-Einstein condensates (BEC) by\nusing a time-dependent optical lattice potential. First, we demonstrate the\ndivision of a BEC into a set of equally populated components by means of time\ndependent control of Landau-Zener tunneling in a vertical lattice potential.\nNext, we apply time dependent optical Bragg mirrors to a BEC oscillating in a\nharmonic trap. We demonstrate high-order Bragg reflection of the condensate due\nto multi-photon Raman transitions, where the depth of the optical lattice\npotential allows for a choice of the order of the transition. Finally, a\ncombination of multiple Bragg reflections and Landau-Zener tunneling allows for\nthe generation of macroscopic arrays of condensates with potential applications\nin atom optics and atom interferometry.\n

We describe a series of atom optics experiments underway at Toronto for investigating tunnelling interaction times of various sorts. We begin by discussing some outstanding issues and confusions related to the question of whether or not superluminal tunnelling can be construed as true faster‐than‐light “signal propagation,” a question which we answer in the negative. We then argue that atom optics is an arena ideally suited for addressing a variety of remaining questions about how, where, and for how long a particle interacts with a tunnel barrier. We present recent results on a modified “delta‐kick cooling” scheme which we have used to prepare Rubidium atoms with one‐dimensional de Broglie wavelengths on the order of an optical wavelength, along with simulations showing that from these temperatures, we will be able to use acousto‐optically modulated dipole‐force barriers to velocity‐select ultracold atom samples ideal for future tunnelling experiments.

This article outlines experiments which have highlighted the rapid development of the field of atom optics since the mid 1980s. The distinguishing features of the components used in atom optics are compared with their conceptual analogues in light optics. The potential for atom optic devices, both demonstrated and predicted, are described. Experiments and applications of this new technology are reviewed, and the article concludes with a synopsis of work in this field currently being undertaken in Australasia.

We discuss the application of spatial light modulators (SLMs) to the field of atom optics. We show that SLMs may be used to generate a wide variety of optical potentials that are useful for the guiding and dipole trapping of atoms. This functionality is demonstrated by the production of a number of different light potentials using a single SLM device. These include Mach-Zender interferometer patterns and the generation of a bottle-beam. We also discuss the current limitations in SLM technology with regard to the generation of both static and dynamically deformed potentials and their use in atom optics.

We demonstrate guiding of cold neutral atoms along a current carrying wire. Atoms either move in Kepler-like orbits around the wire or are guided in a potential tube on the side of the wire which is created by applying an additional homogeneous bias field. These atom guides are very versatile and promising for applications in atom optics.