Interfacing ultracold atoms with nanomagnetic domain walls

This thesis presents the first realisation of a new type of hybrid quantum device based on spintronic technology. We demonstrate an interaction between the magnetic fringing fields produced by domain walls within planar permalloy nanowires and a cloud of ultracold Rubidium 87 atoms. This interaction is manifested through the realisation of a magnetic atom mirror produced by a two-dimensional domain wall array. The interaction is tuned through the reconfiguration of the micromagnetic structure. Analytic modelling of the fringing fields is developed and shows good agreement with calculations based on micromagnetically simulated structures. The accurate and rapid calculation of the fringing fields permits simulation of the resulting atom dynamics, which agrees well with data. In turn, we use the atom dynamics as a probe of the micromagnetic reconfiguration processes that take place and observe a collective behaviour which is both reliably reproducible and in agreement with alternative, conventional magnetometry. We also observe evidence of stochastic behaviour, characteristic of superparamagnetic systems. We consider the development of a more advanced spintronics-based atom chip which will allow for the creation of extremely tight mobile atom traps. We consider the problems associated with ensuring that the trapping potential is adiabatic, sufficiently deep, and technically feasible. In particular we examine techniques to circumvent losses due to Majorana spin-flip transitions. As a result of this study we propose a novel scheme for creating time-averaged potentials via the piezoelectric actuation of magnetic field sources. We show that this technique presents significant fundamental and technical advantages over conventional time-averaging schemes

HARP/ACSIS: A submillimetre spectral imaging system on the James Clerk Maxwell Telescope

This paper describes a new Heterodyne Array Receiver Programme (HARP) and Auto-Correlation Spectral Imaging System (ACSIS) that have recently been installed and commissioned on the James Clerk Maxwell Telescope (JCMT). The 16-element focal-plane array receiver, operating in the submillimetre from 325 to 375 GHz, offers high (three-dimensional) mapping speeds, along with significant improvements over single-detector counterparts in calibration and image quality. Receiver temperatures are $\sim$120 K across the whole band and system temperatures of $\sim$300K are reached routinely under good weather conditions. The system includes a single-sideband filter so these are SSB figures. Used in conjunction with ACSIS, the system can produce large-scale maps rapidly, in one or more frequency settings, at high spatial and spectral resolution. Fully-sampled maps of size 1 square degree can be observed in under 1 hour. The scientific need for array receivers arises from the requirement for programmes to study samples of objects of statistically significant size, in large-scale unbiased surveys of galactic and extra-galactic regions. Along with morphological information, the new spectral imaging system can be used to study the physical and chemical properties of regions of interest. Its three-dimensional imaging capabilities are critical for research into turbulence and dynamics. In addition, HARP/ACSIS will provide highly complementary science programmes to wide-field continuum studies, and produce the essential preparatory work for submillimetre interferometers such as the SMA and ALMA.Comment: MNRAS Accepted 2009 July 2. 18 pages, 25 figures and 6 table

The sublime network; painterly passage and materiality in the post internet era

This practice-led research project investigates painting in the Post Internet era. In the vast database of the Internet, paintings both historical and contemporary are distanced from their makers and contexts. Their diachronic position in a once considered "linear" historical model has been disrupted. The Internet fractures historical narratives, identities and oeuvres and makes them miscellaneous. Through painting I aim to communicate the paradoxical disparity and conflation that occurs between artworks, oeuvres and artistic identities online. Within the rhizomatic space of the Internet, I source and montage various digital examples of Romantic landscape painting into new mashed Romantic images that become source material for my paintings. Here I find synergy between the Post Enlightenment definition of the sublime and a contemporary fascination in the digital sublime - of which the Internet is champion. The project interrogates the Internet in a new and promiscuous way. I use the Internet to identify and disseminate what was once only trusted to the canonical archives of printed literature - the narrative of history

Towards Laser Spectroscopy of Highly Charged Ions: Dynamics of 40Ca+ Ions in a Penning Trap

To date, the most successful quantum field theory is quantum electrodynamics (QED) which offers a fully quantum mechanical description of the electromagnetic interaction between charged particles. Laboratory tests of the theory have been performed for a wide range of field strengths and no significant deviation from the predictions of the theory have been found. For heavy highly charged ions (HCI), the electric and magnetic fields around the nucleus can be orders of magnitude higher than those achievable by conventional means in a laboratory. Therefore, these ions offer a new regime in which the theory should be tested. For HCI above Z > 60, the ground state hyper fine structure splitting (HFS) shifts into the optical region, and becomes accessible to laser light sources. The aim of the SPECTRAP experiment at GSI in Germany, is to perform laser spectroscopy of the HFS in H-like and Li-like HCI, as a test of the corresponding bound-state QED calculations. In order for this to be successful, the weak magnetic HFS transitions need to be measured to a high precision. This will be accomplished in the SPECTRAP experiment by trapping and cooling bunches of HCI, such that the relative precision of the measured transition will be on the level of 10-7, allowing bound-state high order QED calculations to be tested to the level of a few percent. As fluorescence rates will be low, a critical final part in preparing the ions in the trap will be the application of a rotating dipole ('rotating wall') about the magnetic field axis allowing for compression of the ion cloud in the trap, thereby increasing the fluorescence collection efficiency and signal to noise for detection. In London, due to the availability of our own superconducting magnet, we have performed systematic measurements of the dynamics of laser cooled Ca+ ions confined in a Penning trap driven by a rotating wall. With CCD camera imaging, we have measured the fluorescence from a cloud of ions, identified as being a strongly correlated non-neutral plasma, as a function of the rotating wall drive amplitude, frequency, sense of rotation and trap potential. We show that a cloud driven at sufficient amplitude reaches a low-slip regime within the time frame of a single CCD exposure (~ 1s), and that heating resonances are observed on scanning the rotation frequency. These resonances are identified as being associated with the axial motion of the ions in the trap potential, and the lowest order azimuthal plasma modes which are believed to be excited indirectly by a misalignment of the electric and magnetic fields. By operating the rotating wall in the opposite sense of rotation to that used for cloud compression, the excitation of these plasma modes is shown to be a good diagnostic probe of the laser cooled rigid rotation frequency of the cloud, allowing the number density to be inferred from the measurement. These results will allow the SPECTRAP collaboration to define a procedure and set of optimum parameters for use of the rotating wall technique that offers maximum compression of ions needed for the precision spectroscopy of HCI. These results have been accepted for publication in Applied Physics B [1], and were presented at the European Conference for Trapped Ions in September 2010. The in-vacuum confocal fluorescence collection optical design proved valuable in alignment of the imaging system outside the magnet, and successful in increasing the detected fluorescence rates. As a result, the optical design and techniques employed here, have been successfully transferred to the GSI experiment. We also present simulations conducted to optimise the transport and in- flight capture of HCI into the SPECTRAP ion trap from the HITRAP facility at GSI, and report on the first attempts at trapping singly charged Mg+ and Ar+ ions, testing the ability of the system to capture, localise and cool ions

Projective Space: Structuring a Beholder’s Imaginative Response

The thesis explores the reciprocal relationship between an artwork and the space of its reception. It proposes a distinctive position on spatiality and the virtual. The thesis is submitted in two parts: a written thesis (Part One), and a documentation of my own art practice (Part Two). The artwork that comprises the practice component is not that of a painter, and yet the sculptural installations I present allude to perspectival paintings. Utilising perspectival geometry, these site-responsive works engage the threshold between two and three-dimensional representation in a way whereby implicit and actual beholder’s viewpoints are contrasted or fused. The written thesis focuses on the reception of perspectival painting, rather than on my own artworks. Referencing analytical philosophical arguments on representational seeing, and the reception aesthetics of Wolfgang Kemp, it puts forward a distinctive position that contends that while the visual imagination does not define depiction, it plays a pivotal role in supplementing perception in works where the spectator attends to and/or imagines away the threshold separating the real and fictive realms. After Merleau-Ponty, I call such an imaginative engagement seeing-with, which describes a particular use to which painting is put. In providing a strongly felt pictorial depth, I argue that such an implied pictorial space incorporates the space between painting and spectator position. I investigate two categories of works where such imagining facilitates a distinctive access to the picture’s content: (i) paintings containing what Wollheim refers to as an ‘internal spectator’; and (ii) paintings integrated into their architectural settings, where the internal onlooker is fused with the external spectator. I highlight differences afforded internal and external spectators: with the former, the viewer identifies with a spectator who already occupies an unrepresented extension of the ‘virtual’ space; with the latter, the beholder enters that part of the fictive world depicted as being in front of the picture surface, the work thus drawing the ‘real’ space of the spectator into its domain. This distinction mirrors two distinct types of visualization: where a scene is imagined as elsewhere, and where it is situated, juxtaposed with an existing reality. Imagination provides a reciprocity that replicates the experience of our bodily situatedness, in that it structures our implied spatial access to the depicted scene. In establishing a bodily frame of reference, it draws upon nonconceptual content. The thesis tests the philosophical argument against specific paintings, including works that introduce a break from a situated relationship in order to depict the supernatural or the unconscious

Matter in Plotinus's Normative Ontology.

To most interpreters, the case seems to be clear: Plotinus identifies matter and evil, as he bluntly states in Enn. I.8[51] that ‘last matter’ is ‘evil’, and even ‘evil itself’. In this paper, I challenge this view: how and why should Plotinus have thought of matter, the sense-making έσχατον of his derivational ontology from the One and Good, evil? A rational reconstruction of Plotinus’s tenets should neither accept the paradox that evil comes from Good, nor shirk the arduous task of interpreting Plotinus’s texts on evil as a fitting part of his philosophy on the whole. Therefore, I suggest a reading of evil in Plotinus as the outcome of an incongruent interaction of matter and soul, maintaining simultaneously that neither soul nor matter are to be considered as bad or evil. When Plotinus calls matter evil, he does so metonymically denoting matter’s totally passive potentiality as perceived by the toiling soul trying to act upon it as a form-bringer. As so often, Plotinus is speaking quoad nos here rather than referring to ‘matter per se’ (for Plotinus, somewhat of an oxymoron) which, as mere potentiality (and nothing else) is not nor can be evil. In short: matter is no more evil than the melancholy evening sky is melancholy – not in itself (for it isn’t), but as to its impression on us who contemplate it. As I buttress this view, it will also become clear that matter cannot tritely be considered to be the αυτό κακόν as a prima facie-reading of Enn. I.8[51] might powerfully suggest, but that the αυτό κακόν, far from being a principle of its own, has to be interpreted within the dynamics of Plotinus’s philosophical thinking as a unique, though numerously applicable flaw-pattern for all the single kakã (hence the Platonic αύτό). To conclude, I shall offer a short outlook on the consistency of this interpretation with Plotinus’s teaching on the soul and with the further Neoplatonic development of the doctrine of evil

A ROBUST RGB-D SLAM SYSTEM FOR 3D ENVIRONMENT WITH PLANAR SURFACES

Simultaneous localization and mapping is the technique to construct a 3D map of unknown environment. With the increasing popularity of RGB-depth (RGB-D) sensors such as the Microsoft Kinect, there have been much research on capturing and reconstructing 3D environments using a movable RGB-D sensor. The key process behind these kinds of simultaneous location and mapping (SLAM) systems is the iterative closest point or ICP algorithm, which is an iterative algorithm that can estimate the rigid movement of the camera based on the captured 3D point clouds. While ICP is a well-studied algorithm, it is problematic when it is used in scanning large planar regions such as wall surfaces in a room. The lack of depth variations on planar surfaces makes the global alignment an ill-conditioned problem. In this thesis, we present a novel approach for registering 3D point clouds by combining both color and depth information. Instead of directly searching for point correspondences among 3D data, the proposed method first extracts features from the RGB images, and then back-projects the features to the 3D space to identify more reliable correspondences. These color correspondences form the initial input to the ICP procedure which then proceeds to refine the alignment. Experimental results show that our proposed approach can achieve better accuracy than existing SLAMs in reconstructing indoor environments with large planar surfaces

THE FIRST PERSON PERSPECTIVE: LANGUAGE, THOUGHT, AND ACTION

What it is to have a first person perspective? How do we come to understand our own perspective in the world? How do we take into account other people\u27s perspectives in our social and linguistic interactions? This dissertation is an exploration of these issues. But instead of approaching them in the abstract, it aims to shed light on these difficult questions through a series of case studies. First, I examine the role of the first person perspective in our agency, and explain the sense in which it is essential for action. Next, drawing on recent work in psychology, I propose an model of the development of temporal self-understanding in young children. Lastly, I develop a two-level pragmatic theory of epistemic modals