Experiments with ultracold quantum degenerate gases such as Bose-Einstein Condensates or degenerate Fermi gases are at the forefront of modern atomic physics. These systems allow the investigation of complicated quantum-mechanical dynamics of many-body systems in a well controlled environment. Since these gases require temperatures near absolute zero, they must be well isolated from any room temperature environment. Mechanical forces that laser beams exert on atoms are well suited for trapping and manipulating these atoms. The goal of our studies is the investigation of holographic techniques to generate nearly arbitrary lightfields for the manipulation of ultracold quantum gases. The project has three major components: periodic lattices, aperiodic patterns, and computer generated binary holography.
Experiments with ultracold quantum degenerate gases such as Bose-Einstein Condensates or degenerate Fermi gases are at the forefront of modern atomic physics. These systems allow the investigation of complicated quantum-mechanical dynamics of many-body systems in a well controlled environment. Since these gases require temperatures near absolute zero, they must be well isolated from any room temperature environment. Mechanical forces that laser beams exert on atoms are well suited for trapping and manipulating these atoms. The goal of our studies is the investigation of holographic techniques to generate nearly arbitrary lightfields for the manipulation of ultracold quantum gases. The project has three major components: periodic lattices, aperiodic patterns, and computer generated binary holography.
In this habilitation-thesis a collection of 14 experiments is presented. In these experiments we have developed and used novel techniques to control ultracold gases on the quantum level. In brief, Bose-Einstein condensates (BEC) and degenerate Fermi gases of laser-cooled alkali atoms are subjected to specially designed optical and magnetic fields. The fields influence in a coherent way the behavior, properties and dynamics of the gases. On this basis we developed tools to prepare, coherently manipulate, and analyze pre-defined quantum states. With this high level of control, it was possible to investigate interesting physics phenomena, and we were able to achieve several breakthroughs in the field of ultracold atoms. Highlights of our experimental results include the demonstration of phase engineering of a BEC wavefunction where we created solitons in a BEC and studied their propagation. In another experiment we constructed a spatially resolved matter wave interferometer with which we mapped out the phase distribution on a condensate. Illuminating the BEC with a periodic pattern, i.e. an optical lattice, allowed us to study solid states physics phenomena. In a second set of experiments we demonstrated optically tuning of the interaction between atoms with optical Feshbach resonances. Employing either magnetically tunable Feshbach resonances or laser radiation, we were able to produce ground state molecules in well defined quantum states. This led to the production of the first molecular BEC. By tuning the coupling of atom pairs in a Fermi gas of atoms, we could for the first time investigate the so-called BEC-BCS crossover which describes the continuous change from a BEC superfluid to a Bardeen-Cooper Schrieffer (BCS) superfluid. Due to the excellent control on the quantum level, the developed cold atom techniques open up intriguing prospects for future applications and experiments. They represent a general tool box to investigate fundamental physical phenomena in a pure and undisturbed environment. In the future, cold atoms might serve as a testing ground for fundamental theories or as quantum simulators for complex systems.
Ultracold atomic gases can be prepared in laboratory environments with unrivaled control and purity. In one and a half decades the field has evolved from the first Bose condensates in dilute alkali gases to multiple species mixtures and degenerate Fermi systems. Combining quantum degenerate fermions and optical lattices enables the simulation of relevant condensed matter systems. By observing the final state of an atomic sample in a tailored optical potential the system can be used as an analog quantum computer to evaluate Hamiltonians that are computationally impossible to tackle on classical computers. A versatile optical dipole trap has been constructed and characterized. The trap can be converted to an optical lattice, allowing for the investigation of the phase diagram of the two-component, one-dimensional, imbalanced Fermi gas.
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.
Ultracold atoms are used to study various fundamental physics, including many-body system, nonequilibrium dynamics, and find many applications in quantum computing and quantum sensing. In this thesis, we studied the dynamics of ultracold atom gases with controllable two-body interactions. One of the major concerns is to manipulate the atomic states with electromagnetic fields. Here, we will show four projects associated with this topic. The first project is about the Sagnac interferometer based on trapped Bose-Einstein condensate. We explored the dynamics of the atoms and their relation to the sensitivity. We came up with an optimised driving field, and the performance is examined with interactions taken into consideration. The second project is about the quantum dynamics of bosonic atoms in an optical lattice with long-range interactions by Rydberg-dressing. It has been widely studied due to its controllable strength, length and anisotropy, which paves the new approach to engineering exotic quantum states and improving the performance of quantum devices. We found that phase transitions of Mott-insulator, superfluid supersolid, and density wave during a quench process. The correlation of the atoms is studied which reveals the properties of long-range interactions. The third project shows new designs of the magneto-optical trap for atom cooling. They are proposed to be manufactured by 3D printing technology. We simulated their performance and optimised the geometric parameters. The time-response and impedance have also been analysed. The fourth project studies the ground state of Rydberg-dressed fermions from the perspective of Fermi surface deformation. We calculated the deformation manifested by the aspect ratio and the appearance of Cooper pairs. The power-law scaling relations have been found with respect to the laser field, atom density and the quantum number of Rydberg states.
The 1995 observation of Bose–Einstein condensation in dilute atomic vapours spawned the field of ultracold, degenerate quantum gases. Unprecedented developments in experimental design and precision control have led to quantum gases becoming the preferred playground for designer quantum many-body systems. This self-contained volume provides a broad overview of the principal theoretical techniques applied to non-equilibrium and finite temperature quantum gases. Covering Bose–Einstein condensates, degenerate Fermi gases, and the more recently realised exciton–polariton condensates, it fills a gap by linking between different methods with origins in condensed matter physics, quantum field theory, quantum optics, atomic physics, and statistical mechanics. Thematically organised chapters on different methodologies, contributed by key researchers using a unified notation, provide the first integrated view of the relative merits of individual approaches, aided by pertinent introductory chapters and the guidance of editorial notes. Both graduate students and established researchers wishing to understand the state of the art will greatly benefit from this comprehensive and up-to-date review of non-equilibrium and finite temperature techniques in the exciting and expanding field of quantum gases and liquids.