This thesis details the advances made in the use of additive manufacturing to produce magnetic field generating devices and vacuum components for atomic quantum technologies. Cold atomic clouds are used across a suite of quantum sensors including magnetometers, gravimeters and navigational interferometers; as these sensors approach industrial use, they must be translated from laboratory systems to portable devices. The discussion focuses on a number of devices that demonstrate the benefits provided by this approach. Specifically, the devices discussed are a current carrying cylinder trapping device, an ultra-high vacuum (UHV) chamber and a hollow-core coil mount device. This thesis also covers a range of auxiliary developments that have been made alongside the main body of work including a microprocessor-based control system and a pre-cooling stage for cold atom experiments. To begin this thesis reviews the underlying physical phenomena which are exploited when trapping neutral atoms. In particular, it is important to understand the details of the specific case when working with rubidium-87, including the relevant energy levels diagrams and corresponding laser frequencies. This allows for the discussion of the key forces that are used in magneto-optical trapping (MOT) and magnetic trapping including the origin of the magnetic fields generated by these devices using the Biot-Savart law. The key results that are presented in this thesis centre on the efficacy of these devices as atom traps for quantum technologies and atomic experiments. The atom trap cylinder is capable of trapping 108 rubidium atoms at a temperature of 20 µK, demonstrating the feasibility of this approach. The hollow coil mount device presents a viable route for magnetic trapping. Lastly, the UHV chamber operates in the range of 10-10 mbar as necessary for atomic physics experiments. In addition, this thesis reviews the design of a pre-cooling stage for complex atomic experiments and a simplified experimental control system. These are addressed in a systematic approach to the experimental constituents with a comparison between complex fundamental physics experiments and the developments made towards a portable quantum technology device.
This thesis details the advances made in the use of additive manufacturing to produce magnetic field generating devices and vacuum components for atomic quantum technologies. Cold atomic clouds are used across a suite of quantum sensors including magnetometers, gravimeters and navigational interferometers; as these sensors approach industrial use, they must be translated from laboratory systems to portable devices. The discussion focuses on a number of devices that demonstrate the benefits provided by this approach. Specifically, the devices discussed are a current carrying cylinder trapping device, an ultra-high vacuum (UHV) chamber and a hollow-core coil mount device. This thesis also covers a range of auxiliary developments that have been made alongside the main body of work including a microprocessor-based control system and a pre-cooling stage for cold atom experiments. To begin this thesis reviews the underlying physical phenomena which are exploited when trapping neutral atoms. In particular, it is important to understand the details of the specific case when working with rubidium-87, including the relevant energy levels diagrams and corresponding laser frequencies. This allows for the discussion of the key forces that are used in magneto-optical trapping (MOT) and magnetic trapping including the origin of the magnetic fields generated by these devices using the Biot-Savart law. The key results that are presented in this thesis centre on the efficacy of these devices as atom traps for quantum technologies and atomic experiments. The atom trap cylinder is capable of trapping 108 rubidium atoms at a temperature of 20 µK, demonstrating the feasibility of this approach. The hollow coil mount device presents a viable route for magnetic trapping. Lastly, the UHV chamber operates in the range of 10-10 mbar as necessary for atomic physics experiments. In addition, this thesis reviews the design of a pre-cooling stage for complex atomic experiments and a simplified experimental control system. These are addressed in a systematic approach to the experimental constituents with a comparison between complex fundamental physics experiments and the developments made towards a portable quantum technology device.
The development of quantum technologies has been an important topic of research and technological development over the last few years, with numerous projects aiming to exploit cold atoms and Bose-Einstein condensates for sensing applications and probes of fundamental physics. To further develop the emerging applications of new quantum mechanical phenomena, the UK established the a national quantum tech program in 2014. The University of Nottingham, alongside university partners across the country, is currently involved in advancing quantum-based technologies for sensors and metrology applications. A key part of many experiments in this area is the Magneto-Optical Trap, or MOT, which plays a pivotal role in the initial stages of the atom cooling required to reach the nK temperatures necessary to form a condensate. Traditionally, MOTs are typically comprised of multiple pieces of specialised equipment including an ultra-high vacuum chamber, several lasers and magnetic field generating devices, all of which occupy 10's cm in linear dimensions on a laboratory bench and require mains power. As in previous quantum-enabled technologies, including MRI scanners, simulation and optimisation may prove crucial in reducing the size, weight and power requirements of such systems, and for improving their performance. Consequently, it is natural to apply such optimisation methods to emerging quantum technologies, in order to meet the restrictions on experimental size, weight and power necessary the practical cold atom-based sensing systems. As it forms a crucial part of many cold atom quantum technologies, the MOT is a natural initial target for simulation and subsequent optimisation. To develop system design capabilities, this thesis firstly presents three optimisation methods for permanent magnets. One of these builds on previous work to optimise ferromagnetic films for Ioffe-Pritchard arrays (chapter \ref{Magnetic Plate Optimisation}), the others are novel optimisation methods, drawing on more general approaches and on shimming methods frequently used in MRI. Permanent magnets were chosen for use in MOTs in order to reduce the required power and volume of current experimental equipment. While each of the three optimisation methods have different capabilities, two were particularly powerful for designing high field fidelity MOTs. One of these methods was developed specifically to design magnet systems for use with the 3D printed vacuum chamber of the Innovate UK-funded OptaMOT project, illustrating its potential to develop experimental systems. The magnetic field was generated to high accuracy by using the new optimisation algorithm, presented in chapter \ref{Spherical Harmonic Optimisation}, by using mass produced magnets, thereby offering improved practicality over designs that require, expensive, custom-made magnets. With the aim of improving the holistic design capabilities required to advance MOTs, simulation software for the dynamics of atoms in MOTs was also developed. The simulations were capable of modelling the dynamics of atom clouds in both a typical 6 beam MOT and an optical molasses arrangement. It was also used to elucidate the action of a significantly more complicated beam arrangement exploiting more advanced physical phenomena. Remarkably, the arrangement, developed by Hub partners at The University of Southampton, experimentally shows a high atom number and the potential presence of a restoring force without an applied magnetic field. The laser beam geometry also exhibits an unusual dependence of the final atom number on laser beam detuning and power. The simulations provided insights into the potential origins of this dependence (suggesting a combination of beam interference and an additional detuning from the laser fields), whilst confirming that the laser beam configuration alone creates a damping force, as with an optical molasses arrangement. However, the origins and presence of a restoring force still, unfortunately, remain unknown.
A key element in the study of cold atoms, and their use in emerging quantum technologies, is trapping the atoms in an ultra-high vacuum (UHV) chamber. Many methods have been used to trap atoms including atom chips and magneto-optical traps (MOTs). However, the bulky apparatus, and current-carrying coils, used so far in most MOTs restrict the reduction of power and physical size, as required for quantum technology applications. The advent of 3D printing technology now offers a new route to making MOTs with current paths that can be freely shaped and shrunk to several centimetres, thereby helping to reduce the power consumption and simplify the production of the MOT itself. In this paper, we present designs for 3D printed MOTs and analyse their performance by using COMSOL simulations. We predict that the 3D-printed conductors can create magnetic fields with gradients around 15 G/cm and passing through zero, as required for atom trapping, with Joule heating as low as 0.2 W.
Abstract Recent advances in the understanding and control of quantum technologies, such as those based on cold atoms, have resulted in devices with extraordinary metrological performance. To realise this potential outside of a lab environment the size, weight and power consumption need to be reduced. Here we demonstrate the use of laser powder bed fusion, an additive manufacturing technique, as a production technique relevant to the manufacture of quantum sensors. As a demonstration we have constructed two key components using additive manufacturing, namely magnetic shielding and vacuum chambers. The initial prototypes for magnetic shields show shielding factors within a factor of 3 of conventional approaches. The vacuum demonstrator device shows that 3D-printed titanium structures are suitable for use as vacuum chambers, with the test system reaching base pressures of 5 ± 0.5 × 10−10 mbar. These demonstrations show considerable promise for the use of additive manufacturing for cold atom based quantum technologies, in future enabling improved integrated structures, allowing for the reduction in size, weight and assembly complexity.
Novel quantum technologies and devices place unprecedented demands on the performance of experimental components, while their widespread deployment beyond the laboratory necessitates increased robustness and fast affordable production.We show how the use of additive manufacturing, together with mathematical optimization techniques and innovative designs, allows the production of compact lightweight components with greatly enhanced performance.We use such components to produce a magneto-optical trap that captures approximately 2 × 10 8 rubidium atoms, employing for this purpose a compact and highly stable device for spectroscopy and optical power distribution, optimized neodymium magnet arrays for magnetic field generation, and a lightweight additively manufactured ultrahigh-vacuum chamber.We show how the use of additive manufacturing enables substantial weight reduction and stability enhancement, while also illustrating the transferability of our approach to experiments and devices across the quantum technology sector and beyond.
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.
Atom interferometers have been used to measure accelerations and rotations in many laboratories around the world. They have demonstrated very high long-term stability, making them well suited for development into an inertial navigation system. The next stage of development towards a full navigation system is to move these laboratory demonstrators into the field, and improve their resilience to the effects of a more turbulent environment. This thesis presents the development of the first transportable quantum inertial sensor at the Centre for Cold Matter at Imperial College London, developing on the laboratory-based systems which have already been demonstrated. Rubidium-87 atoms are delivered into an ultra-high vacuum chamber with a 2D+ magneto optical trap (MOT), before being trapped in a 3D MOT and cooled to below 5 µK using polarisation gradient cooling. Atoms are efficiently prepared in a magnetically insensitive energy level, before a narrow velocity class of atoms is selected, to reduce the effect of thermal dephasing mechanisms. A three pulse, π/2−π−π/2, interferometer sequence coherently splits, reverses and recombines the atom cloud, and the atomic energy level populations are recorded after the third pulse using fluorescence imaging. Interference fringes have been demonstrated for a number of different interferometer times in the laboratory, and initial characterisation of the fringe contrast has been performed. In addition to in-laboratory characterisation, data from three field trials, alongside the Royal Navy, are presented. The trials have enabled us to benchmark the system’s performance outside of the laboratory, and highlight the areas of development required for improved system performance in future field trials.