The confinement and control of atomic clouds, at temperatures measured in nanokelvin, has become a valuable tool for physicists. As a source of new physics, development of cooling techniques has led to innovative new ways to probe the nature of reality. Of particular note are experiments carried out on new and exotic states of matter such as the Bose-Einstein condensate, unseen before the advent of these techniques. Likewise, the potential for applications outside of the lab is extensive and encompasses navigation, timekeeping, quantum communication and quantum computing. Manipulating cold atoms in the presence of a so-called ‘atom chip’ (a millimetre-scale electronic device) is currently considered the future of miniaturising these experiments and measurements, but since they still require precisely locked and stabilised lasers and predominantly must take place in the ultra-high vacuum regime, quantum control relies on an extensive and well-established infrastructure of optics, electronics, vacuum chambers and pumps. This encumbrance has slowed down the transition from chip-in-a-lab experiments to lab-on-a-chip technologies. This thesis is an account of work carried out in the development of enabling technologies which will accelerate this transition, including details of prototype devices made using established semiconductor and MEMS planar fabrication techniques. The construction and testing of an apparatus for anodically and eutectically bonding die-scale samples in ultra-high vacuum is described, along with an analysis and characterisation of some of its products.
The confinement and control of atomic clouds, at temperatures measured in nanokelvin, has become a valuable tool for physicists. As a source of new physics, development of cooling techniques has led to innovative new ways to probe the nature of reality. Of particular note are experiments carried out on new and exotic states of matter such as the Bose-Einstein condensate, unseen before the advent of these techniques. Likewise, the potential for applications outside of the lab is extensive and encompasses navigation, timekeeping, quantum communication and quantum computing. Manipulating cold atoms in the presence of a so-called ‘atom chip’ (a millimetre-scale electronic device) is currently considered the future of miniaturising these experiments and measurements, but since they still require precisely locked and stabilised lasers and predominantly must take place in the ultra-high vacuum regime, quantum control relies on an extensive and well-established infrastructure of optics, electronics, vacuum chambers and pumps. This encumbrance has slowed down the transition from chip-in-a-lab experiments to lab-on-a-chip technologies. This thesis is an account of work carried out in the development of enabling technologies which will accelerate this transition, including details of prototype devices made using established semiconductor and MEMS planar fabrication techniques. The construction and testing of an apparatus for anodically and eutectically bonding die-scale samples in ultra-high vacuum is described, along with an analysis and characterisation of some of its products.
This thesis details the work carried out in the development towards a fully miniaturised integrated atom chip. The main focus of the project so far has been on the construction of miniaturised vacuum chambers, the study of the eutectic bond and the manufacturing of integrated electric feedthroughs, together with the development of new cold atom trap geometries. Current cold atom technologies rely on the use of bulky optical systems and large vacuum chambers. We propose the miniaturisation of the entire system into a device comparable in size with a match box. Afirst step towards this goal is the miniaturisation of the vacuum system and atomic source. In the first part of this thesis we present planar microfabrication techniques, such as anodic bonding and eutectic bonding, as a solution for providing hermetic seals. Several partially working devices i.e miniaturised vacuum chambers with rubidium atom sources are presented and compared to commercial rubidium cells. As ultimately our integrated atom chips will be used in metrology and sensing devices, they require current-carrying wires within the vacuum. Towards this purpose we propose a method of building hermetically sealed electrical feedthroughs through the process of glass reflow in thick silicon substrates. The second part of this thesis outlines a brief theory towards cooling atoms, together with new geometries designed for use with miniaturised devices and the attempts of achieving a functional integrated atom chip. Finally, we present the development of a new method for achieving a cold atom source without the use of magnetic fields.
The field of atom chips is a relatively new area of research which is rapidly becoming of great interest to the scientific community. It started out as a small branch of cold atom physics which has quickly grown into a multidisciplinary\nsubject. It now encompasses topics from fundamental atomic and quantum theory, optics and laser science, to the engineering of ultra sensitive sensors.\n\nIn this thesis the first steps are taken towards a truly integrated atom chip device for real world applications. Multiple devices are presented that allow the trapping, cooling, manipulation and counting of atoms. Each device presents a new component required for the integration and miniaturisation of atom chips\ninto a single device, capable of being used as a sensor.\n\nInitially, a wire trap was created capable of trapping and splitting a cloud of BoseEinstein condensate (BEC) for use in atom interferometry. Using this chip a BEC has been successfully created, trapped and coherent splitting of this cloud has been achieved.\n\nSubsequently, the integration and simplification of the initial trapping process was approached. In all the experiments to date, atoms are initially collected from a warm vapour by a magneto-optical trap (MOT). This thesis presents a new approach in which microscopic pyramidal MOTs’ are integrated into the chip itself. This greatly reduces the number of optical components and helps to simplify the process significantly.\n\nAlso presented is a method for creating a planar-concave micro-cavity capable of single atom detection. One such cavity consists of a concave mirror fabricated in silicon and the planar tip of an optical fibre. The performance of the resonators\nis highly dependent on the surface roughness and shape profile of the concave mirrors therefore a detailed study into the fabrication technique and its effects on these parameters was undertaken. Using such cavities single atom detection has been shown to be possible. These cavities have also been sccessfully integrated into an atom wire guide.\n\nFinally a co-sputtered amorphous silicon/titanium (a-Si/Ti) nanocomposite material was created and studied for its use as a novel structural material. This material is potentially suitable for integrated circuitry (IC)/Micro-electromechanical-\nsystems (MEMS) integration. The material’s electrical and\nstructural properties were investigated and initial results suggest that a-Si/Ti has the potential to be a compelling structural material for future IC/MEMS integration.\n\nTo build all of these devices, a full range of standard microfabrication techniques was necessary as well as some non standard processes that required considerable process development such as the electrochemical deposition.\n\nThis thesis presents a tool box of fabrication techniques for creating various components capable of different tasks that can be integrated into a single device. Each component has been successfully demonstrated in laboratory conditions. This represents a significant step toward a real world atom chip device.
The laser cooling, trapping and manipulating of neutral atoms has become a valuable tool for scientists, providing innovative ways to probe the nature of reality and giving rise to transformative devices in the fields of precise measurement and quantum information processing. Unlike traditional complex and bulky atomic experimental facilities, atom chips, through the design, fabrication of surface-patterned microstructures, and the integration of devices on the substrates, can precisely control the magnetic, electric or optical fields on a micro-nano scale with low power consumption. It can realize strong trapping as well as coherent atomic manipulation. Since atom chip was first proposed twenty years ago, it has built a robust quantum platform for miniaturizing and integrating quantum optics and atomic physics tools on a chip. In this paper, first, we briefly review the development history of atom chips, then introduce the basic knowledge of micro potential traps and micro guides based on on-chip current-carrying wires. Afterwards, the key technologies about the chip material, design, fabrication, characterization and integration of atom chips are discussed in detail. We not only focus on the currently most active and successful areas - current carrying wires, but also look at more visionary approaches such as to the manipulation of atoms with real nano structures, say, carbon nano tubes. The design and fabrication principles of ideal atom chips are discussed as well. In the forth part, the worldwide plans and research projects involving with atom chip technologies are summarized, showing that many countries see this as an important foundational technology. Following that, the major developments in the application fields including atom clocks, atom interferometer gyroscope, cold atom gravimeter, etc are described. Finally, the challenges faced by atom chips towards practical application are pointed out and the prospects for their subsequent development are depicted.
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.
In order to take quantum mechanical systems out of the lab and produce practical devices, a method of miniaturizing and integrating apparatus components is needed. In the context of ultracold atomic gas experiments, the ideal method of achieving this miniaturization is the implementation of atom chip technology. By depositing micro-scale current carrying wires onto planar substrates, it is possible to create a magnetic trap capable of confining a cloud of neutral atoms in sufficient proximity to the chip surface for solid state devices to interact with the cloud. This thesis presents our lab’s first steps towards creating an atom chip capable of confining a cloud of rubidium-87. The chip prototypes were developed with the intent to incorporate them into the hybrid system apparatus within our lab. The chips are intended to serve as a platform for facilitating the interaction between the atomic gas ensemble and mesoscopic solid-state devices, allowing for the hybridization of the two systems. In this work I describe the design of the trapping wire configuration and the fabrication of the first two generations of chip prototypes. Additionally, I provide numerical simulations of the produced magnetic field, from which estimates of the trap frequency and depth can be calculated. Finally, I introduce some basic characterization tests of the absolute current limitations and resistive behavior of the chip wires, and the dimensional uniformity of the fabricated wire profiles.
Using matter wave interferometry to perform high precision measurements is an exciting field of modern day physics and engineering. Physical constants and anomalies too small to observe with classical devices can be probed and measured with quantum technology. The ability to control the wave nature of a specific particle opens up a vast set of methodologies engineered for the given particle. The most complete toolboxes exist for alkali metals such as rubidium and cesium. The atomic structure of strontium provides a number of advantages in further developing these methods and technologies, especially in the resolution of spectroscopic measurements.A promising method of matter-wave control utilizes optical waveguides and atomic properties to trap and guide matter waves. Using laser cooling techniques, atoms are cooled to microkelvin temperatures before being loaded onto the nanophotonic chip, thus receiving the appropriate name, atom-on-chip devices. The ability to manufacture the photonic waveguides in a multitude of different arrangements shows promise in being able to develop atomtronic devices which are equivalent to electronic devices, but utilize matter-waves of neutral atoms instead of electrons.The heart of our novel technology is an ultra-high vacuum (UHV) apparatus with sample loading capabilities. In this thesis, I discuss the design and construction of the apparatus to provide quick turn over between loading nanophotonic devices and experimental trapping by separation of the main chamber from a load lock. The ultimate pressures in both reach 3.8times10−11 and below 1times10−11 Torr and initial trials were conducted with a 36-48 hour turn over between loading a chip at atmosphere, and inserting it into the UHV main chamber. These metrics beats other groups by an order of magnitude in pressure and others week-long loading time. Continual improvements are being made to further decrease this time.