Non-uniform electric and magnetic fields provide a versatile tool to manipulate and control the motional states of polarizable and magnetizable particles in a remote and non-destructive fashion. However, as the field force falls dramatically with the particle size, the manipulation of sub-micron particles against their Brownian motion at room temperature is challenging. This requires the use of strong field gradients and high intensities which makes the miniaturization of the field-producing structures preferable. Other motivations to develop miniaturized trapping structures are the improved positional control and reduced power consumption provided by them. The objective of this thesis is to pursue the realization of two novel miniaturized manipulation tools based on static electric and magnetic fields by modeling the trapping potentials, and fabricating the trapping structures. In particular, a method to fabricate a three-dimensional periodic nanoelectrode array for nanoparticle manipulation is described. The method is based on tapering a microstructured photonic crystal fiber and filling the contracted capillaries with a conductive material. Based on numerical simulations, such nanoelectrodes can be used to produce electric-field patterns with nanometer scale features for control and assembly of nanoparticles at room temperature. The other miniaturized device considered in this thesis is a permanent-magnet chip for atom and nanoparticle manipulation. Microscopic magnetic-domain patterns recorded in a ferrite-garnet (FG) film can be used to create microscopic traps for nanoparticles at room temperature and for atoms cooled to AK-range temperatures. The magnetic-domain patterns can be created by using a conventional magneto-optical recording technique. In addition, we have developed a novel technique to record the domain patterns all-optically. These techniques allow one to record and reconfigure the domain patterns in situ. In essence, arbitrary two-dimensional trapping structures can be readily produced. Our FG chip has many advantages over the conventionally used current-carrying wire structures. Most important of them are optical transparency, reconfigurability, and the ability to produce nearly noiseless and strong magnetic fields without any electric-power consumption. In our laboratory, this kind of microscopic magnetic atom traps have been demonstrated experimentally using 85Rb atoms. In all-optical recording the local magnetization direction in the FG film is controlled purely optically by adjusting the beam parameters of the recording laser. This magnetization-reversal phenomenon is intriguing from both fundamental and technological points of view and can be used not only in the magnetic chip technology, but also in other magnetic and optical device applications in which the use of electricity is undesirable. As an example, a novel concept of all-optical memory elements that allow writing and erasing of information in three dimensions, is introduced in this thesis. Both the nanoelectrode array and magnetic FG chip could be integrated with other nano- and microfabricated components to built multifunctional devices on a single substrate. With this respect, the work introduced in this thesis constitutes one more step forwards the "lab on a chip" technology.
Non-uniform electric and magnetic fields provide a versatile tool to manipulate and control the motional states of polarizable and magnetizable particles in a remote and non-destructive fashion. However, as the field force falls dramatically with the particle size, the manipulation of sub-micron particles against their Brownian motion at room temperature is challenging. This requires the use of strong field gradients and high intensities which makes the miniaturization of the field-producing structures preferable. Other motivations to develop miniaturized trapping structures are the improved positional control and reduced power consumption provided by them. The objective of this thesis is to pursue the realization of two novel miniaturized manipulation tools based on static electric and magnetic fields by modeling the trapping potentials, and fabricating the trapping structures. In particular, a method to fabricate a three-dimensional periodic nanoelectrode array for nanoparticle manipulation is described. The method is based on tapering a microstructured photonic crystal fiber and filling the contracted capillaries with a conductive material. Based on numerical simulations, such nanoelectrodes can be used to produce electric-field patterns with nanometer scale features for control and assembly of nanoparticles at room temperature. The other miniaturized device considered in this thesis is a permanent-magnet chip for atom and nanoparticle manipulation. Microscopic magnetic-domain patterns recorded in a ferrite-garnet (FG) film can be used to create microscopic traps for nanoparticles at room temperature and for atoms cooled to AK-range temperatures. The magnetic-domain patterns can be created by using a conventional magneto-optical recording technique. In addition, we have developed a novel technique to record the domain patterns all-optically. These techniques allow one to record and reconfigure the domain patterns in situ. In essence, arbitrary two-dimensional trapping structures can be readily produced. Our FG chip has many advantages over the conventionally used current-carrying wire structures. Most important of them are optical transparency, reconfigurability, and the ability to produce nearly noiseless and strong magnetic fields without any electric-power consumption. In our laboratory, this kind of microscopic magnetic atom traps have been demonstrated experimentally using 85Rb atoms. In all-optical recording the local magnetization direction in the FG film is controlled purely optically by adjusting the beam parameters of the recording laser. This magnetization-reversal phenomenon is intriguing from both fundamental and technological points of view and can be used not only in the magnetic chip technology, but also in other magnetic and optical device applications in which the use of electricity is undesirable. As an example, a novel concept of all-optical memory elements that allow writing and erasing of information in three dimensions, is introduced in this thesis. Both the nanoelectrode array and magnetic FG chip could be integrated with other nano- and microfabricated components to built multifunctional devices on a single substrate. With this respect, the work introduced in this thesis constitutes one more step forwards the "lab on a chip" technology.
We describe experiments on the trapping of atoms in microscopic magneto-optical traps on an optically transparent permanent-magnet atom chip. The chip is made of magnetically hard ferrite-garnet material deposited on a dielectric substrate. The confining magnetic fields are produced by miniature magnetized patterns recorded in the film by magneto-optical techniques. We trap Rb atoms on these structures by applying three crossed pairs of counterpropagating laser beams in the conventional magneto-optical trapping geometry. We demonstrate the flexibility of the concept in creation and in situ modification of the trapping geometries through several experiments.
Ultracold atomic gases can be utilised as extremely sensitive probes of their surrounding environment. In particular, samples of ultracold atoms confined using chip-based microtraps are an ideal tool for mapping electric and magnetic field landscapes. Over the course of this thesis, a new experiment capable of performing surface microscopy using magnetically trapped clouds of cold rubidium-87 atoms has been built. The focus of the work is on the design and construction of the experimental system, which must incorporate many different aspects for manipulating thermal atomic gases, with a view to positioning them at sub-micron distances from special surfaces. This reduced atom-surface separation is necessary for implementing a high resolution, high sensitivity magnetic field sensor with cold atoms. Although current microfabrication techniques easily enable trapping at distances on the order of micrometres, several distance-dependent surface effects - such as the Casimir-Polder force, Johnson-Nyquist noise, and stray potentials - eventually impede magnetic trapping at the sub-micron level. These surface effects can greatly modify the confining potentials, which reduces the trap depth and consequently leads to an additional loss rate of atoms from the trap. We have explored the possibility of using special surfaces such as nano-membranes of silicon nitride and graphene, which have reduced atom- surface interactions, to enable trapping distances at the sub-micron level. A multilayer printed circuit board chip has been designed to form an initial magnetic trap and then transport the cloud of atoms to a desired location over the samples. This chip, along with various samples, is mounted on a custom-made electrical feedthrough designed to make connections to all conductor that are inside the vacuum chamber. The initial cloud of cold atoms can then be prepared in the central region of the chip and delivered to the location of the samples on either side. The experimental system is able to routinely capture over 10^8 rubidium-87 atoms at a temperature of 80 micro-Kelvin in a magneto-optical trap using a novel scheme of five laser beams. A method is demonstrated for enhancing the atom number in the magneto-optical traps by a factor of two by using laser beams with two slightly different frequencies. Atoms from the magneto-optical trap are then transferred to a purely magnetic trap formed by the wires on the printed circuit board chip. Time-dependent currents in the chip wires then create a dynamic potential, which is shown to successfully transport the atomic sample over a distance of 12 millimetre with minimal atom loss. This thesis describes the development of the apparatus in detail, along with careful characterisation of the cold cloud at various stages of the experimental sequence. Initial results on the long distance atom transport are presented. Finally, the experimental results of the two frequency magneto-optical trap for atom number improvement are discussed.
During the past two decades the dramatic developments in cooling and trapping of gaseous atomic samples has produced a variety of techniques to manipulate the external and internal atomic states with electromagnetic fields. The research efforts so far have mainly focused on studying the fundamental aspects of modern quantum physics, although numerous practical applications, e.g., in integrated matter-wave optics and quantum information processing, are expected to soon be added to the already established atom-optics products, such as atomic clocks and acceleration sensors. One of the most promising foundations for the practical applications of Bose-Einstein condensates (BECs) and coherent matter waves is the technology based on the creation of microscopic atom traps on the surface of a solid substrate. This trapping technique has recently been used to successfully control the motion of microscopic atomic samples and to significantly simplify the creation of BEC.\n\nThe main research topic of this thesis is the development and design of surface-mounted atom traps on transparent dielectric substrates. Such traps could provide an extra flexibility and stability for the experiments, since they would allow unimpeded control of atoms with laser light and provide reduction of magnetic-field fluctuations associated with the thermal motion of free electrons in the substrate material. The thesis describes several novel approaches to the creation of such surface traps by superimposing repulsive evanescent optical waves with strongly localized magnetic or electric fields. These fields can be produced by either conductive or permanently magnetized, optically transparent patterns imprinted in a thin layer on a transparent dielectric substrate. The evanescent wave can also be used to cool the atoms in a gravitational field before loading them into the microtrap. The lateral confinement of the atoms on the evanescent wave can be realized with a thin-walled hollow laser beam, the creation of which is demonstrated in the thesis. The thesis also describes certain general aspects concerning evanescent-wave cooling. In particular, the influence that multiple reabsorption of resonance-frequency photons in a cloud of evanescent-wave cooled atoms has on the cooling efficiency is investigated. Also, a theoretical model based on classical statistical mechanics and thermodynamics is introduced to show how a microtrap on an evanescent-wave mirror can be used to decrease the temperature, increase the phase-space density, and provide temperature conserving spin-polarization of the atoms.
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.
This thesis describes and characterizes a setup to conduct experiments combining the fields of cold atoms and nanophotonics. Furthermore, a series of numerical simulations is employed to deepen of atom transport under experimentally realistic conditions. The study of cold atoms is usually fundamental in nature and a very clean approach to investigate the laws of physics. High purity samples of atoms are cooled down to millikelvins or microkelvins. The potential landscape for the atoms can be carefully controlled using lasers and/or magnetic fields. Since the atoms' responses to electric, magnetic or electromagnetic fields are known with very high fidelity, any deviations to the state the atoms are prepared in can be precisely measured. Nanophotonics is the study of light close to or beyond the diffraction limit. In this region the field-like nature of light starts to play a role. By confining light in sub-wavelength-sized structures, high peak intensities can be achieved, giving rise to exciting non-linear optics phenomena. The strong field gradient that can be created allows, for instance, precise spectroscopy measurements, phase-sensitive sub-wavelength microscopy, as well as producing highly receptive sensing devices. Combining cold atoms and nanophotonics creates strong synergy effects. It gives access to strong coupling of light and matter. The scalability of nanophotonics now extends to atomic physics. Atoms can be trapped, coupled and manipulated at very small length scales, and in large numbers. Moreover, the potential landscape for atoms is highly customizable. The rubidium isotope 87 is used in this setup. A cloud of rubidium atoms is gathered and cooled in a two dimensional magneto-optical trap (MOT). Since the atoms are only cooled in two dimensions, they are free to escape in the third dimension and load a following three dimensional MOT. The atoms are now cooled further, compressed and loaded into an optical dipole trap. This dipole trap transports the atoms close to a sample inside the vacuum chamber. A moving optical lattice, or optical conveyor belt, brings the atoms then close to the sample surface. Now experiments can be conducted, studying the interaction of cold atoms and strongly confined light. The atom transport down to the sample surface shows some unexpected behaviour: the atoms seem to spread through the optical lattice during transport. A combination of microscopic and macroscopic numerical simulations, including genetic algorithms, are used to deepen our understanding of the underlying physics. This also allows us to get access to experimental variables that cannot be directly obtained.
Abstract Atom chips provide flexible technologies for implementing modern concepts in quantum optics, quantum measurement, and quantum information processing. Atom chips are miniature devices that confine, control and manipulate cold atoms using electric, magnetic, and light fields. Due to the shrinkage of scale, arbitrary magnetic traps can be generated from current sources outside the chip’s vacuum compartment, in contrast to a traditional setup. This makes it easy to change trap configurations in an experiment that involves rapid prototyping of quantum states and quantum trajectory designs in free space. In this work, we show relevant parameters needed for transferring a cold atom cloud at the recoil limit from a magneto-optical trap (MOT) to an area close to the atom chip. To create a movable magnetic potential for this transfer, we used the MOT coils and an additional pair of coils in an anti-Helmholtz configuration. The properties of the movable potential were obtained by performing the Computer Simulation Tool (CST EM Studio suite®). Furthermore, an appropriate magnetic trap on a chip is developed, based on the simulation from COMSOL Multiphysics. We used a magnetic field gradient of around 20 G/cm to transport the cold atom with a distance over 20 mm with a temperature gain below 100 micro-Kelvin. The simulation results are based on an atom chip with a size of 2×2 cm2 and a copper wire thickness of 2 mm. The atom chip consists of Z, U and I-shaped wires that generate a quadrupole magnetic field. The resulting field minimum can be made at least 7 mm away from the chip surface.