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.
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.
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.
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.
We report the transport of magnetically trapped cold atoms over a large distance. Atoms are captured in a magneto-optical trap (MOT) and loaded into a magnetic quadrupole trap. The quadrupole potential is then moved over a distance of 33 cm into an ultra-high-vacuum (UHV) chamber using a chain of quadrupole coils. By running suitable currents through the quadrupole coil pairs the trapping geometry of the potential is maintained during the transport process, thus minimizing heating of the trapped atom cloud. Magnetically trapped 87Rb atoms at an initial temperature of $T=125 \ensuremath{\mu}\mathrm{K}$ were heated by less than $20 \ensuremath{\mu}\mathrm{K}$ during the transport process, and up to 109 atoms were transferred into the UHV chamber. Due to the spatial separation of the final magnetic trap and the MOT we have been able to capture atoms in the MOT, while storing magnetically trapped atoms in the UHV chamber.
We have constructed in our laboratory two rectangular shaped current carrying coils in accordance with the parameters used in our design so that they can be put in use in the Two Dimensional Magneto Optical Trap (2D-MOT)to obtain very high value of Optical Depth(OD). The dimensions of the coils are 8cm x 10cm. When put in anti-Helmholtz configuration as required in a 2D-MOT, these coils generate magnetic field such that it becomes zero along a line bisecting the space between the two coils. The magnetic field gradient near the zero magnetic field line is measured to be 3.33 Gauss/cm when the current passing through the coils is 3.5A. We have also made measurements at other values of current and found, as expected, this gradient increases with current. These results match nicely with the estimated values and hence a significant step forward towards the experimental realization of the design proposed by us.
Cold atoms form the backbone of many quantum technology applications, including quantum computation, sensing, and networking. These experiments require a robust cold atom source, precise control of beam parameters, and large optical access. We demonstrate a compact cesium magneto-optical trap (MOT) directly loaded from background vapor, with a footprint of 34 × 56 cm2. The quadrupole and compensation coils are mounted on additively manufactured components, eliminating the need for water cooling and minimizing eddy currents, which enables fast magnetic field switching with a measured settling time of 240 μs. Finite element analysis confirms the mechanical robustness and thermal stability of the coil mounts. The MOT achieves 5 × 106 atoms at a density of 109 cm-3, with a temperature of 76 ± 2 μK, demonstrating a reliable and compact platform suitable for quantum technology experiments.
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.