Abstract : During 2005, a new basic research effort was begun to better understand confined cold atom systems and determine if atom interferometry for the detection of rotation was possible utilizing spatially and temporally modulated magnetic fields generated using currents running through traces on microchips. During the next seven years, significant progress has been made in evaluating the constraints posed by both theory and practical experimental considerations. This report encompasses three of these studies: collisional decoherence in trapped interferometers, adjustable microchip ring-traps, and atom chips on direct bonded copper substrates. The first of these describes an analytical model developed to describe the effects of collisions between atoms in a harmonic magnetically confined atom interferometer. The second describes a method to create an agile circular magnetic waveguide for deBroglie waves on a microchip, while the third presents the use of direct bonded copper (DBC) for the straightforward fabrication of high power atom chips. Each of these efforts has incrementally added to our cold atom interferometry knowledge base and has enabled the future construction of a working atom chip based interferometer for the ultrasensitive detection of rotation.
Abstract : During 2005, a new basic research effort was begun to better understand confined cold atom systems and determine if atom interferometry for the detection of rotation was possible utilizing spatially and temporally modulated magnetic fields generated using currents running through traces on microchips. During the next seven years, significant progress has been made in evaluating the constraints posed by both theory and practical experimental considerations. This report encompasses three of these studies: collisional decoherence in trapped interferometers, adjustable microchip ring-traps, and atom chips on direct bonded copper substrates. The first of these describes an analytical model developed to describe the effects of collisions between atoms in a harmonic magnetically confined atom interferometer. The second describes a method to create an agile circular magnetic waveguide for deBroglie waves on a microchip, while the third presents the use of direct bonded copper (DBC) for the straightforward fabrication of high power atom chips. Each of these efforts has incrementally added to our cold atom interferometry knowledge base and has enabled the future construction of a working atom chip based interferometer for the ultrasensitive detection of rotation.
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.
Abstract : Gyroscopes based on ultracold atom interferometry have the potential to exhibit an intrinsic sensitivity larger by a factor of 4 x 1010 than for light-based interferometers. One of the major technical challenges for the advancement of atom optics and development of practical guided matter wave interferometers is the realization of coherent beam splitters. The overall focus of our research program is to develop a physical understanding of the conditions needed for coherent beam splitting and transport and use this knowledge to implement atom chip based interferometers using clouds of ultracold atoms. In this report we describe our experimental apparatus in detail and discuss the current progress towards interferometric measurements with clouds of ultracold atoms in a chip-based magnetic waveguide.
The system comprised of an atom strongly coupled to photons, known as cavity quantum electrodynamics (QED), provides a rich experimental setting for quantum information processing, both in the implementation of quantum logic gates and in the development of quantum networks. Moreover, studies of cavity QED will help elucidate the dynamics of continuously observed open quantum systems with quantum-limited feedback. To achieve these goals in cavity QED, a neutral atom must be tightly confined inside a high-finesse cavity with small mode volume for long periods of time. Microfabricated wires on a substrate---known as an atom chip---can create a sufficiently high-curvature magnetic potential to trap atoms in the Lamb-Dicke regime. We have recently integrated an optical fiber Fabry-Perot cavity with such a device. The microwires allow the on-chip collection and laser cooling of neutral atoms, and allow the magnetic waveguiding of these atoms to an Ioffe trap inside the cavity mode. Magnetically trapped intracavity atoms have been detected with this cavity QED system. A similar experiment employing microdisks and photonic bandgap cavities is nearing completion. With these more exotic cavities, a robust and scalable atom-cavity chip system will deeply probe the strong coupling regime of cavity QED with magnetically trapped atoms. Atom chips have found great success in producing and manipulating Bose-Einstein condensates and in creating novel atom optical elements. An on-chip BEC has been attained in a miniaturized system incorporating an atom chip designed for atom interferometry and for studies of Josephson effects of a BEC in a double-well potential. Using similar microfabrication techniques, we created and demonstrated a specular magnetic atom mirror formed from a standard computer hard drive. This device, in conjunction with micron-sized charged circular pads, can produce a 1-D ring trap which may prove useful for studying Tonks gases in a ring geometry and for creating devices such as a SQUID-like system for neutral atoms. This thesis describes the fabrication and employment of these atoms chips in experiments at both Caltech and Munich, the latter in collaboration with Professors Theodore Haensch and Jakob Reichel at the Max Planck Institute for Quantum Optics.
Since their initial production in 1995, the study of Bose-Einstein Condensates (BECs) has offered exciting new insights into many fields including quantum mechanics and solid state physics. Atom chips, non-conducting surfaces with conducting lithographic traces printed on them, have proven successful in generating lower power magnetic traps for the formation of BECs. The combination of their lower power consumption, small form factor, and dense traps makes atom chips a promising way to face a ubiquitous challenge in the study of BECs: the effect of the earth’s gravitational field. To avoid these effects the NASA Cold Atom Laboratory aims to create BECs aboard the International Space Station (ISS) using an atom chip. This thesis presents the development of a similar atom chip based BEC experiment at Bates College, which will serve as a functional testbed for future research aboard the ISS. Both a theoretical background and a description of the experimental process by which a BEC is formed on an atom chip are provided. This process is primarily driven by laser cooling and magnetic trapping techniques. A 2D+ Magneto-Optical Trap (MOT), loaded from vapor pressure, is used as a slowed source of 87Rb in order to create a 3D MOT. We present measurements of the performance of both MOTs, and outline a path forward to condensation on the chip-based magnetic trap through use of radiofrequency evaporative cooling.
We report on progress for a couple of experiments on manipulating cold atoms on a chip for quantum sensing. The first experiments are directed towards developing a compact atom interferometer on an atom chip using a double-well potential. The interferometer uses 87Rb atoms magnetically confined in an atomic waveguide produced by wires on the surface of a lithographically patterned chip. Finite element modeling of combinations of different current configurations with various external bias fields indicated a means of coherently splitting the atomic cloud through dynamically adjusting the currents and bias fields. In these experiments we investigate real-time transformations between different double-well configurations adiabatically and non-adiabatically, and study their effects on the initially trapped atoms. Coherence properties of the two atomic wavepackets are examined. In another set of experiments we investigate the properties of bosons confined to (quasi) one dimension in our magnetic waveguide. When the atom-atom repulsive interaction becomes much larger than the kinetic energy, bosons confined in one dimension can enter a new state of matter, the Tonks-Girardeau gas, in which they behave like non-interacting fermions. However, the bosons can still occupy the same momentum state and therefore the gas cannot be fully described by either Bose-Einstein or Fermi-Dirac statistics. This transition has been observed in optical lattices but not in magnetic atom chip waveguides. We discuss the conditions for obtaining a Tonks-Girardeau gas with 87Rb atoms in our atom chip waveguide as well as a novel signature for observing the transition in our system.
Atom chips are an excellent tool for studying ultracold degenerate quantum gases, due to the high degree of controllability afforded by the precise potentials generated from the current-carrying microfabricated wires on the chip surface. The geometries of the trapping potentials are inherently capable of realising extreme aspect ratios, and therefore creating model systems with effectively reduced dimensionality, particularly the theoretically-tractable one-dimensional Bose gas. In addition, the temporal tunability makes it possible to impart non-adiabatic changes on the trapping potentials, allowing experimental investigation of samples which have been brought out of equilibrium - a situation which is not fully theoretically understood. This thesis describes the implementation, development and characterisation of an experimental system for producing the first Bose-Einstein condensates of atomic rubidium 87 gas trapped on the surface of an atom chip in Nottingham. Such an apparatus is very complex and requires careful characterisation in order to run in a stable and reliable way. Details of the experimental setup are thoroughly outlined, including the vacuum system, lasers, electronics, computer control and timing, and the optical imaging system. A newly installed compact two-dimensional magneto-optical trap provides an loading rate of 5e7 atoms per second for loading a three-dimensional mirror-magneto-optical trap with 1.5e8 atoms, at a temperature of 300uK within 10s. The cloud is then sub-Doppler cooled to 50uK, and spin-polarised with 96% purity into the |F=2,mF=+2> ground state within 5ms, in preparation for loading a purely magnetic trap. A millimeter sized copper Z-shaped conductor located beneath the atom chip surface creates a Ioffe-Pritchard magnetic trap, into which the laser cooled cloud is loaded with 70% efficiency, and can be held with a vacuum-limited lifetime of 40s. Evaporative cooling then pre-cools the sample to below 20uK within 10s, to allow the subsequent loading into potentials created by the atom chip with 100% efficiency. A final evaporation stage then cools the cloud below the phase transition temperature of 800nK, resulting finally in pure BECs with 105 atoms confined using the atom chip. Key measurements of various properties of the trapped condensates are presented, which are important in order to characterise the system fully, and to compare with theoretical expectations. In particular, included are the variation of condensate fraction with temperature, the BEC expansion dynamics, and the condensate lifetime in the trap, for example. Finally, it is demonstrated how BECs can be produced on the atom chip without the use of external macroscopic coils, achieved by using novel, integrated sheet structures located beneath the chip surface - unique to this experimental system - to create the necessary bias fields.