This thesis focusses on the use of a Digital Micromirror Device (DMD) to produce spatially and temporally varying optical potentials for the manipulation of ultracold atoms. I discuss the apparatus used to generate ultracold atomic samples as well as that used to manipulate them, including a comparison of the various light sources used with the DMD. Here I demonstrate the advantages in image quality that can be achieved using a superluminescent diode. I also report on work which uses the capability to produce spatially and temporally controlled potentials to engineer a synthetic dimension of harmonic oscillator sites, forming a lattice consisting of 10s of lattice sites on which Bloch Oscillations are demonstrated. Finally I describe simulations which demonstrate the clustering behaviour of quantised vortices in a Bose-Einstein condensate when arranged in linear structures, as could be done by the method of phase imprinting using a DMD. I demonstrate the use of a cluster detection algorithm which is novel in the field of quantised vortices, and show that in many cases, vortex clusters can be modelled by methods similar to those used for single vortices.
This thesis focusses on the use of a Digital Micromirror Device (DMD) to produce spatially and temporally varying optical potentials for the manipulation of ultracold atoms. I discuss the apparatus used to generate ultracold atomic samples as well as that used to manipulate them, including a comparison of the various light sources used with the DMD. Here I demonstrate the advantages in image quality that can be achieved using a superluminescent diode. I also report on work which uses the capability to produce spatially and temporally controlled potentials to engineer a synthetic dimension of harmonic oscillator sites, forming a lattice consisting of 10s of lattice sites on which Bloch Oscillations are demonstrated. Finally I describe simulations which demonstrate the clustering behaviour of quantised vortices in a Bose-Einstein condensate when arranged in linear structures, as could be done by the method of phase imprinting using a DMD. I demonstrate the use of a cluster detection algorithm which is novel in the field of quantised vortices, and show that in many cases, vortex clusters can be modelled by methods similar to those used for single vortices.
We report on the realization and characterization of optical potentials for ultracold atoms using a superluminescent diode. The light emitted by this class of diodes is characterized by high spatial coherence but low temporal coherence. On the one hand, this implies that it follows Gaussian propagation similar to lasers, allowing for high intensities and well-collimated beams. On the other, it significantly reduces those interference effects that lead to severe distortions in imaging. By using a high-resolution optical setup, we produce patterned optical potentials with a digital micromirror device and demonstrate that the quality of the patterns produced by our superluminescent diode is consistently and substantially higher than those produced by our laser. We show that the resulting optical potentials can be used to arrange the atoms in arbitrary structures and manipulate them dynamically. Our results can open new opportunities in the fields of quantum simulations and atomtronics.
The development of novel trapping potentials for degenerate quantum gases has been an important factor driving experimental progress in the field. The introduction of spatial light modulators (SLMs) into quantum gas laboratories means that a range of configurable geometries are now possible. Here we demonstrate the production of arbitrary and dynamic high-resolution traps for Bose-Einstein condensates (BECs) using a (1200 x 1920) pixel digital-micromirror device (DMD) and commercially available microscope objectives. Direct imaging of the DMD provides significant advantages over phase-based SLMs, while still providing high resolution projected patterns. We find that atoms confined in a hybrid optical/magnetic or all-optical potential can be patterned using repulsive blue- detuned (532 nm) light with 630(10) nm full-width at half-maximum (FWHM) resolution, while imaging at 780 nm similarly achieves 960(80) nm resolution FWHM, within 5% and 8% of the diffraction limit respectively. This performance is > 7 times improved over previously reported DMD trapping. The result is near arbitrary control of the atomic distribution over the spatial extent of the BEC trapping volume. Furthermore, we produce time-averaged potentials with the DMD, demonstrating the ability to produce multiple grayscale levels with minimal heating of the atomic cloud. These techniques, along with the high level of dynamic control afforded by DMDs, will enable the realization and control of diverse optical potentials for superfluid dynamics and atomtronics applications with quantum gases.
The implementation of spatial light modulators (SLMs) in quantum gas experiments has allowed the realization of ever more complex trapping geometries. As ultracold atoms may be sensitive to perturbations of the trapping potential at the 1% level, the high contrast ratios of digital micromirror devices are proving advantageous for use in optical trapping. Our laboratory pursues configurable traps based on the direct (nearly diffraction limited) imaging of a digital micromirror device (DMD). We achieve highly flexible potentials using commercially available microscope objectives external to our vacuum chamber that directly project the DMD to the atom plane, producing optical traps over an area of 130 μm × 200 μm, with a resolution of 630(10) nm full width at half maximum (FWHM) at 532 nm illumination. We combine these potentials with a horizontally propagating TEM00 or TEM01 Hermite-Gaussian optical sheet that provides vertical confinement. With the dynamic control enabled by the maximum full-frame rate of 20 KHz and on-board storage of <13,000 frames of the DMD, we study the transport of atoms and superfluid dynamics in configurable trapping geometries. Using the fast frame rate of the DMD we also produce intermediate grey levels that complement half-toning techniques for producing optimized grayscale patterns.
Bose-Einstein condensates are superfluids which when engineered under suitable laboratory conditions support dissipationless flows and facilitate the development of quantum enhanced applications. Realising those suitable conditions requires experimental technologies which enable the complete dynamical control of the superfluid density and velocity profiles. This thesis conceives and demonstrates several dynamical controls using optical potentials formed using commercially available spatial-light-modulator technologies, and constitutes important progress toward many future experiments and the realisation of practical applications.Experimental systems and control sequences are designed using complimentary acousto-optic deflection and digital micromirror spatial light modulator technologies, rather than magnetic field based approaches, given their inherently favourable spatial and temporal resolutions. An experimental apparatus which includes a time-averaged acousto-optic controlled potential is constructed to generate toroidal potentials suitable for developing inertial rotation sensors. Density and phase manipulation strategies are developed using that apparatus which prepare condensates with arbitrarily controllable wavefunctions. Complementary digital micromirror based adaptations are subsequently developed during this project.Corrugations across the condensate density distributions are reduced using an iteratively corrected spatial light modulator configuration. Rigorous and generalised scan requirements are established for engineering time-averaged potentials; numerical methods are conceived which facilitate the simulation of these systems. The combination of the feedforward density control and time-averaging phase control enable the deterministic preparation of persistent currents around multiply connected condensates. These capabilities enable experiments into many-body groundstates, superfluid turbulence, atomtronics and metrology.Spatial light modulator trapping sequences geared toward the study of Onsager vortices, vortex dipole optics, inertial rotation sensing and wake turbulence are specifically developed. Several upgraded experimental systems are finally designed using knowledge gained during this thesis, which enable these various applications in future. This thesis therefore constitutes significant progress toward several important experimental investigations using dynamically controllable optical trapping technologies.
Programable spatial light modulators (SLMs) have significantly advanced the configurable optical trapping of particles. Typically, these devices are utilized in the Fourier plane of an optical system, but direct imaging of an amplitude pattern can potentially result in increased simplicity and computational speed. Here we demonstrate high-resolution direct imaging of a digital micromirror device (DMD) at high numerical apertures (NA), which we apply to the optical trapping of a Bose-Einstein condensate (BEC). We utilise a (1200 x 1920) pixel DMD and commercially available 0.45 NA microscope objectives, finding that atoms confined in a hybrid optical/magnetic or all-optical potential can be patterned using repulsive blue-detuned (532 nm) light with 630(10) nm full-width at half-maximum (FWHM) resolution, within 5% of the diffraction limit. The result is near arbitrary control of the density the BEC without the need for expensive custom optics. We also introduce the technique of time-averaged DMD potentials, demonstrating the ability to produce multiple grayscale levels with minimal heating of the atomic cloud, by utilising the high switching speed (20 kHz maximum) of the DMD. These techniques will enable the realization and control of diverse optical potentials for superfluid dynamics and atomtronics applications with quantum gases. The performance of this system in a direct imaging configuration has wider application for optical trapping at non-trivial NAs.
Physics of ultra cold atoms and molecules is one of the most rapidly developing areas of the modern atomic, molecular, optical physics and quantum optics.This area covers several sub-areas of diverse importance, but definitely two trends can be easily identifies: i) fundamental research on properties of ultra cold atoms and molecules, and in particular atomic and molecular condensates trapped and lattice gases; here the fundamental questions of nature and form of phase transitions in degenerate systems are being posed and studied; ii) more applications oriented research on ultracold atoms and molecules, involving in particular applications in precision measurements, atomic clocks, frequency standards, atom and molecule interferometry, quantum information, quantum engineering, "super" chemistry etc.This thesis concerns both of these major trends.The applications, or more specifically quantum engineering aspect are discussed in the first four chapters of the thesis, which deal with optical manipulations of ultra cold gases, in particular optical generation of vortices in Bose condensates, quasi-solitons in Fermi gases, and retarded dipole-dipole interactions in Bose, or Fermi gases.This thesis consists of four main chapters.Chapter 2, "Optical generation of vortices in Bose Einstein Condensates".In this chapter we study theoretically the generation of vortices by phase imprinting in trapped Bose-Einstein condensates.Phase imprinting is achieved by passing a short off-resonance laser pulse through an appropriately designed absorption plate, and impinging it on a condensate.We answer the fundamental question of how the circulation and the vortex are introduced into the system, and discuss the creation of vortex arrays.We discuss vortex dynamics and interactions in such configurations.Various methods of vortex detection based on interference combined with Bragg scattering are also analyzed.In Chapter 3, "Fermionic 'Solitons'" we investigate in detail the concept of low energy excitations of ultra cold Fermi gases.This excitations are generated using the same idea of phase imprinting as that employed in the generation of vortices in BEC.We address in this chapter some questions concerning the generation (via phase imprinting) of soliton-like solutions in a single-component Fermi gas of neutral atoms at zero and finite temperatures.By using both numerical and analytical calculations, we find the conditions under which it is possible to find in non-interacting Fermi gases, quasisolitons which resemble the properties of solitons in non-linear integrable equations.We present the results for both spatially homogeneous and trapped cases, and emphasize the importance of Fermi statistics and the absence of interactions for the existence of such solutions.In Chapter 4, "Generating Dipole Condensate" we keep studying the possibilities of optical manipulations of ultracold gases.In particular, we study two different ways to laser-induce dipole-dipole interactions in trapped Bose-Einstein condensates.The first one employs the fact that those atoms in high Rydberg states posses a large dipolar moment.We first analyze the idea of imposing the dipole moment as a time average over short stroboscopic pulses.These pulses are coherently transporting the atoms from the ground atomic state to some high Rydberg state and back.The second idea is based on the observation that in strong static or oscillatory electric fields, atoms polarize and acquire dipole moment.We analyze the possibilities and limitations of inducing such a high electric field using lasers of low frequency.In Chapter 5, "Dipolar BCS", we continue our study of trapped fermionic gases, with the analysis of the BCS transition in trapped dipolar fermionic gases.We find that the critical strength of the dipole-dipole interaction to achieve BCS pairing, depends on the trap geometry.We find the particular form of this dependence, and present the solutions for the order parameter.This first chapter is meant as a general introduction to the thesis.This introduction is by no means exhaustive, and should be rather treated as a collection of basic facts concerning ultra cold gases, without rigorous derivations.The last subsection of the introductory chapter, discusses very briefly the most important achievements and trends in the field and the current state of the art.