This thesis reports on the development of novel techniques for the detection and manipulation of cold gases of neutral atoms. The research presented focusses on the implementation of a photonic waveguide chip into an atom optics experiment. Our photonic chip consists of 12 parallel waveguides with a 10 µm pitch and a 16 µm trench in the centre. A wire subchip underneath the photonic chip can create magnetic fields to guide atoms into the trench and hold them there. The electric field of the light mode propagating through the waveguides has a 1/e radius of 2:2 µm. This small light mode can readily be used for local measurements of the atomic density. This thesis describes the setup of the waveguide chip experiment and gives a detailed characterisation of the interaction between light and atoms in the trench. Additionally, I report on a scheme for detecting atoms while minimising the number of scattered photons for a given precision of the measurement. We use a light beam synthesized from two frequencies tuned to either side of the atomic resonance and detect the differential phase shift they acquire when passing through an atomic cloud by referencing the beat between the two frequencies to a local oscillator. Unlike most similar techniques our beam does not contain a carrier signal and can therefore be balanced around the atomic resonance in order to cancel the mean optical dipole force on the atoms.
This thesis reports on the development of novel techniques for the detection and manipulation of cold gases of neutral atoms. The research presented focusses on the implementation of a photonic waveguide chip into an atom optics experiment. Our photonic chip consists of 12 parallel waveguides with a 10 µm pitch and a 16 µm trench in the centre. A wire subchip underneath the photonic chip can create magnetic fields to guide atoms into the trench and hold them there. The electric field of the light mode propagating through the waveguides has a 1/e radius of 2:2 µm. This small light mode can readily be used for local measurements of the atomic density. This thesis describes the setup of the waveguide chip experiment and gives a detailed characterisation of the interaction between light and atoms in the trench. Additionally, I report on a scheme for detecting atoms while minimising the number of scattered photons for a given precision of the measurement. We use a light beam synthesized from two frequencies tuned to either side of the atomic resonance and detect the differential phase shift they acquire when passing through an atomic cloud by referencing the beat between the two frequencies to a local oscillator. Unlike most similar techniques our beam does not contain a carrier signal and can therefore be balanced around the atomic resonance in order to cancel the mean optical dipole force on the atoms.
This thesis introduces the first demonstration of a monolithic, micro-fabricated, multi-channel, optical-waveguide chip to measure ultra-cold atomic clouds. The optics consist of an array of 12 independent junctions, which are separated by only 10 μm and have large atom-photon coupling. The integrated and scalable design is presented, along with an atom chip for mounting the optical waveguide chip and magnetically trapping and handling ultra-cold atoms. The experimental apparatus which was built to accommodate this new chip set is described, along with a new experimental control programme which was developed to accommodate the scalability requirements of the new chip. The chip was optically, mechanically and magnetically characterised and cold atoms with densities up to 10-² μm-³, corresponding to 1 atom at a time inside the waveguide mode, were detected with this new kind of chip using absorption and fluorescence techniques. Subsequently, the atoms were utilised to diagnose light polarisation and intensity within the optical-waveguide chip. For future use, various detection methods adapted to the optical-waveguide chip were considered to minimise photon scattering and thus heating of a trapped ultra-cold sample of atoms.
This thesis describes atomic physics experiments performed using a microfabricated photonic waveguide chip: a device that enables the interaction of cold atoms with an array of 12 microscopic light beams emitted by optical waveguides, inside a microscopic trench that has been cut into the chip, across all of the waveguides. The chip uses standard cold-atom control techniques along with readily available photonics technologies to provide an integrated atomic physics device that is not ‘scalable’ so much as already scaled. We describe experiments where atoms are driven into the trench using magneto-optical traps and magnetic traps. In the latter case, the large, homogeneous magnetic field that is present during the atom-light interaction allows us to observe polarization-dependent effects in absorption signals from the trench. Vacuum difficulties have limited the efficiency of rf-driven evaporative cooling in our magnetic trap to 0.4 (with a final phase-space density of 2×10^-5). To circumvent this issue, we have developed a novel evaporative cooling process, in which a dimple potential, comprised of an optical trap and a magnetic trap, is used to perform cycles of isentropic trap deformation and selective atom removal. Using this cooling process increases our evaporative cooling efficiency to 1.2. Various other cooling strategies that involve the dimple are also investigated. Using the dimple, we achieve a phase-space density of 0.04. Having cooled the cloud using the dimple, we move it into the trench and measure absorption signals of 50%, much larger than those achieved previously. We investigate the possibility of producing microscopic optical dipole traps in the trench by sending red-detuned light through the waveguides, and show results of preliminary experiments looking at light shifts.
Atom optics has been a highly active field of research with many scientific breakthroughs over the past two decades, largely due to successful advances in laser technology, microfabrication techniques, and the development of laser cooling and trapping of neutral atoms. This dissertation details several atom optics experiments with the motivation to develop tools and techniques for precision atom wave interferometry. It provides background information about atom optics and the fundamentals behind laser cooling and trapping, including basic techniques for cold gas thermometry and absorptive detection of atoms. A brief overview of magnetic trapping and guiding in tight wire-based traps is also provided before the experimental details are presented. ❧ We developed a novel laser source of 780 nm light using frequency-doubled 1560 nm fiber amplifier. This laser system provided up to a Watt of tunable frequency stabilized light for two Rb laser cooling and trapping experiments. One system generates Bose-Einstein condensates in an optical trap while the second is based on atom chip magnetic traps. The atom chip system, detailed in this thesis, was designed and built to develop the tools necessary for transport and loading large numbers of cold atoms and explore the potential for guided atom interferometry. Techniques and results from this experiment are presented, including an efficient magnetic transport and loading method to deliver cold atom to atom chip traps. We also developed a modeling tool for the magnetic fields formed by coiled wire geometries, as well as planar wire patterns. These models helped us design traps and determine adiabatic transportation of cold atoms between macro-scale traps and micro-traps formed on atom chips. Having achieved near unity transfer efficiency, we demonstrated that this approach promises to be a consistent method for loading large numbers of atoms into micro-traps. Furthermore, we discuss an in situ imaging technique to investigate magnetic field contours of the traps and the dynamics of atoms within those confining potentials. We also controlled the propagation along the atom chip guides by accelerating atoms with longitudinal magnetic gradients, and investigated an atom focusing scheme. ❧ While the atom chip wire guides perform a role analogous to optical fibers guiding light waves, ""free space"" cold atoms offer great opportunity for precision interferometry. We describe a second on-going atom optics experiment that measures gravity gradients using a pair of atom fountain interferometers separated by one meter. We have demonstrated Gravity Gradiometer resolution down to 4x10⁻⁹ g/m using a 40 kg test mass. The atomic physics subsystem is described in detail, including the vacuum, cold atom source, optics, magnetic coils and shields, and vibration isolation and compensation. The system is designed to be a compact, robust, transportable instrument, taking strides towards future gravity gradient measurements in the field. In the realm of space applications, there has been interest for micro-gravity science experiments aboard the International Space Station, along with instrument development for gravity mapping of Earth and planetary bodies with satellite-based instruments. Furthermore, there are ground-based applications for gravity imaging of local density distributions, precision measurement of gravity, as well as proposals for redefining the kilogram, detecting gravitational waves and determining the Gravitational constant.
This project focuses on a novel experimental method for interfacing cold atoms with optical waveguides. This relies on the introduction of cold atoms into microscopic laser-drilled holes that are perpendicular to the propagation axis of the waveguide. Direct interfacing of cold atoms with the guided mode of a waveguide is an attractive mechanism by which to create atom-photon interfaces, as the small mode area increases the interaction rate. Unlike many previous approaches, this technique can be applied in almost any existing waveguide system, including chip-based waveguide arrays and other complex environments. It therefore has great promise as a way of creating hybrid atom-photon quantum devices. Using this method, we demonstrate coupling between cold atoms and the light propagating in the core of an untapered single-mode optical fibre. This was achieved by laser-drilling a cylindrical, transverse hole (30 μm diameter) through the core of the fibre. Ensembles of cold caesium atoms can be tightly confined through an optical dipole trap within the microscopic void. Probe light, resonant with the Cs D2 line, is then coupled into the fibre. By measuring the transmitted optical power through the interface, it was determined that up to 87% of the probe power could be absorbed by the atoms. The corresponding optical depth per unit length of the atom cloud is over 700 cm^(-1), higher than any value reported to date for a comparable system. This will be a key parameter for the miniaturisation of atom-optical systems as well as for enhancing spatial resolution in sensing applications. The dependence of this absorption on several experimental parameters was also characterised and found to be in line with theoretical expectations. The atomic transition is not noticeably broadened by the presence of the fibre. We have also carried out numerical simulations of light transmission across wave-guide junctions of this type, proving that tailored hole geometries can enable enhanced optical transmission. The achievable degree of improvement is such that it is conceivable to place the void within an optical resonator, for example using laser-written Bragg gratings, and to achieve the strong coupling between the atoms and the guided light. Altogether this work demonstrates the potential of this technique to interface atoms with tightly confined light, allowing for integration in otherwise purely photonic circuits. In such environment the interaction between the atomic ensemble and the light can act as a node for the storage and processing of quantum information.
In this work we present the results of studies of one-dimensional (1D) and twodimensional (2D) optical lattices on a chip.We have developed a method to create 1D and 2D optical lattices above an optical waveguide.The method is based on the destructive interference of the evanescent waves of two modes of the waveguide, resulting in a periodic array of nodes above the waveguide surface.For blue-detuned light, this constitutes an array of optical dipole traps for neutral atoms.One pair of modes coupled into a ridge waveguide creates a 1D array of nodes in this manner, and two orthogonal pairs of modes in a slab waveguide result in a 2D array of nodes.Computational analysis of our method showed that these optical atom chips may be suitable for use as a quantum register, and for studies of atom-surface interactions between the trapped atoms and the waveguide surface.Using realistic waveguide materials and laboratory laser parameters we found that for a laser power of ~100 mW nodes can be created ~100 nm above the waveguide surface.The nodes constitute atom traps that are ~1mK deep, and have trap frequencies ~1MHz and ground state sizes of ~10 nm.The spacing between traps is ~1 µm enabling individual addressing with a focused laser beam.iii With the implementation of two-qubit gates in mind, initial investigations of extensions of the basic 2D optical lattice were conducted.Computational results for a counter-propagating 2D optical lattice with very close trap spacing (~λ/4) in one dimension, and for a 2D optical lattice with adjustable spacing between pairs of traps in one dimension are presented.An experimental setup for the realization of the proposed 2D optical lattices on a chip was designed and built.Several cooling and trapping steps necessary to prepare a cold atom sample for loading of the 2D optical lattice have been implemented successfully.In the course of previous studies of atom-surface interactions, a novel surfaceionization detector for 2D imaging of neutral atom samples was built and characterized.We find a detection efficiency ~50 %, a spatial resolution of 20 µm and a time response < 1/30 s. iv To my family.v ACKNOWLEDGMENTS First and foremost I would like to thank my advisor Greg Lafyatis for everything that he taught me.I also want to thank Frank DeLucia for always being there with his advice when I needed it.I appreciate Eric Herbst and Junko Shigemitsu for being willing to serve on
This thesis proposes improvements on techniques for the coherent control of photon-photon interactions mediated by a cloud of cold atoms. Atoms cooled and trapped in a MOT can be loaded into a hollow, photonic crystal waveguide to ensure light coupled into the waveguide is localized on the tightly confined atoms. The low temperature of the atoms decreases decoherence rates, and improves coherent light-matter interactions, such as electromagnetically induced transparency and slow light. Predictions are made for two future experiments using this system, modulating of the phase of a laser beam with a much weaker one, and modulating the transmission of a laser through two photon absorption. These predictions indicate that the phase of a 0.1μW laser beam can be modulated by as much as one milliradian per weak laser photon, and that a 800pW laser beam can modulate the transmission of a comparably powerful laser by as much as 60%. Both of these predictions would be improvements on results for similar experiments performed with warm atoms.