In this thesis, we develop, validate and apply a non-destructive, spin-sensitive probing method for ultracold gases of sodium. By exploiting the polarization dependence of the atom-light interaction, the method combines optical hardware with computational reconstruction to access spin-resolved density and magnetization distributions from a single, minimally destructive exposure. The thesis is structured in three parts; firstly, we describe the experimental platform for making, probing and manipulating sodium spinor Bose–Einstein condensates, including laser cooling, optical and magnetic trapping, and radio-frequency techniques for coherent spin preparation. In the second part, we develop the core measurement technique of spin-dependent off-axis holography is developed, and evaluate its robustness to technical noise and the magnetic field variations. The reconstruction and analysis pipeline is presented in detail, with special emphasis on the background noise suppression using an inpainting technique based on principal component analysis. In the final part, the method is applied to investigate dynamics in spin-1 ultracold atomic sodium. To that end, we introduce the theory of three-level spin systems and propose magnetization-preparation and precise Zeeman-sublevel readout schemes, which are experimentally verified. These tools are then used to investigate spin diffusion and spin mixing dynamics, and the formation and evolution of spin domains. This work establishes spin-dependent off-axis holography as a powerful tool for probing spinor quantum gases. The techniques developed here enable efficient and minimally destructive imaging of spin dynamics, and provide new opportunities for studying non-equilibrium spin phenomena and magnetism in ultracold atomic systems.
In this thesis, we develop, validate and apply a non-destructive, spin-sensitive probing method for ultracold gases of sodium. By exploiting the polarization dependence of the atom-light interaction, the method combines optical hardware with computational reconstruction to access spin-resolved density and magnetization distributions from a single, minimally destructive exposure. The thesis is structured in three parts; firstly, we describe the experimental platform for making, probing and manipulating sodium spinor Bose–Einstein condensates, including laser cooling, optical and magnetic trapping, and radio-frequency techniques for coherent spin preparation. In the second part, we develop the core measurement technique of spin-dependent off-axis holography is developed, and evaluate its robustness to technical noise and the magnetic field variations. The reconstruction and analysis pipeline is presented in detail, with special emphasis on the background noise suppression using an inpainting technique based on principal component analysis. In the final part, the method is applied to investigate dynamics in spin-1 ultracold atomic sodium. To that end, we introduce the theory of three-level spin systems and propose magnetization-preparation and precise Zeeman-sublevel readout schemes, which are experimentally verified. These tools are then used to investigate spin diffusion and spin mixing dynamics, and the formation and evolution of spin domains. This work establishes spin-dependent off-axis holography as a powerful tool for probing spinor quantum gases. The techniques developed here enable efficient and minimally destructive imaging of spin dynamics, and provide new opportunities for studying non-equilibrium spin phenomena and magnetism in ultracold atomic systems.
In this thesis, we develop, validate and apply a non-destructive, spin-sensitive probing method for ultracold gases of sodium. By exploiting the polarization dependence of the atom-light interaction, the method combines optical hardware with computational reconstruction to access spin-resolved density and magnetization distributions from a single, minimally destructive exposure. The thesis is structured in three parts; firstly, we describe the experimental platform for making, probing and manipulating sodium spinor Bose–Einstein condensates, including laser cooling, optical and magnetic trapping, and radio-frequency techniques for coherent spin preparation. In the second part, we develop the core measurement technique of spin-dependent off-axis holography is developed, and evaluate its robustness to technical noise and the magnetic field variations. The reconstruction and analysis pipeline is presented in detail, with special emphasis on the background noise suppression using an inpainting technique based on principal component analysis. In the final part, the method is applied to investigate dynamics in spin-1 ultracold atomic sodium. To that end, we introduce the theory of three-level spin systems and propose magnetization-preparation and precise Zeeman-sublevel readout schemes, which are experimentally verified. These tools are then used to investigate spin diffusion and spin mixing dynamics, and the formation and evolution of spin domains. This work establishes spin-dependent off-axis holography as a powerful tool for probing spinor quantum gases. The techniques developed here enable efficient and minimally destructive imaging of spin dynamics, and provide new opportunities for studying non-equilibrium spin phenomena and magnetism in ultracold atomic systems.
The three experiments described in this thesis investigate fundamental properties of ultracold atoms. Using laser cooling and evaporative cooling, a dilute gas of sodium atoms is cooled to ~100 nK. Under these circumstances a Bose-Einstein condensate (BEC) forms, where millions of atoms collapse into the lowest energy state of the system and share a macroscopic wavefunction. The experiments are done in an ultrahigh vacuum and the atoms are manipulated remotely using laser beams, magnetic fields, and RF-fields. Using ultracold atoms allows unprecedented control over the internal and external degrees of freedom of the system, making it very suitable for precision measurements. Ultracold atoms also serve as a model system for more complicated or remote fields such as solid-state physics and cosmology. In the first experiment the refractive index of an ultracold bosonic gas is studied. The atomic clouds are analyzed for temperature and number of particles using nearly non-destructive phase-contrast imaging. After each pulse of probe light a small fraction of the atoms is lost, while the cloud is simultaneously slightly heated. This makes it possible to study the scattering rate as a function of temperature using only a single sample. It is observed that the scattering rate increases below the critical temperature for BEC by more than a factor of 3 compared to the classical value. This enhancement is in good agreement with the predictions by theoretical work that takes two-body correlation and the Lorentz-Lorenz correction into account. The method is also used to perform calorimetry on the Bose gas and directly measure the heat capacity of the BEC. The second chapter deals with magnetism in ultracold gases. When cooling an ultracold gas containing different spin components below the critical temperature for BEC, stable magnetic domains form. The appearance of these domains and the dynamics of the domain walls are studied. The spin mixture is prepared by performing an RF-sweep on ground state atoms in the presence of a magnetic field. Spin dynamics are induced by applying magnetic gradients. Spin drag, which is the transport coefficient responsible for damping spin currents, was measured in a two-component system. Furthermore a new method for spin resolved phase contrast imaging is presented, which is used to study time evolution in situ non-destructively. The last experiment focuses on spontaneous symmetry breaking. When passing a continuous phase transition, spontaneous symmetry breaking causes the development of domains with an independently chosen order parameter. The domains are separated by boundary defects. In this experiment the spontaneous creation of solitons was observed, which are boundary defects in the phase of the condensate, as well as magnetic domain walls, which are the boundary defects in the magnetization. Through the Kibble-Zurek mechanism it is possible to determine the critical exponents that characterize the phase transition. The critical exponents are predicted to be universal, i.e. do not depend on the microphysics of the system, so the results from our ultracold atoms lab can help answer universal questions for example from cosmology and from the early universe.
We introduce a noninvasive imaging technique based on spin-dependent off-axis holography for spin-1 Bose-Einstein condensates. Utilizing a dual reference beam strategy, this method records two orthogonal circular polarization components of a single probe beam. The circular birefringence of spin-polarized atoms induces differing complex phase shifts in the polarization components of the light, which are reconstructed from the interference patterns captured on camera. Our approach enables spin- and density-resolved imaging of both phase and amplitude information in situ on a submillisecond timescale with minimal disturbance to the condensate. We explore the technique's efficacy under various background static fields, demonstrating its sensitivity to the quantization axis of the atoms and confirming its effectiveness.
Optical imaging plays a central role in ultracold atom experiments by enabling quantitative measurements of atomic density, temperature, atom number, and condensate dynamics. Achieving high-fidelity absorption imaging requires a well-characterized optical system with accurately calibrated magnification and spatial resolution. In this work, I designed, implemented, and experimentally characterized a dual-view optical imaging platform for future absorption imaging of ultracold sodium atoms. The system consists of two independent three-lens relay imaging systems providing top and side views of the atomic sample. Two low-magnification configurations with nominal magnification 0.6 were developed for imaging the relatively large sodium magneto-optical trap (MOT), while higher-magnification configurations with nominal magnifications of 4 and 10 were designed for Bose–Einstein condensate (BEC) imaging. The work included the integration and optimization of the laser cooling and trapping apparatus, improvements to the magnetic-field control system, and the alignment and calibration of both imaging paths. Characterization using a laser and a USAF 1951 resolution target yielded measured magnifications of 0.653 ± 0.033 and 0.521 ± 0.016 for the side and top MOT imaging systems, with corresponding spatial resolutions of 13.92 µm and 9.84 µm. The BEC imaging systems achieved measured magnifications of 4.094 ± 0.060 (top) and 10.817 ± 0.172 (side), with spatial resolutions of 9.84 µm and 6.20 µm, respectively. These measurements agree well with the theoretical diffraction-limited resolutions of 7.19 µm for the 0.6 and 4 magnification systems and 2.87 µm for the 10 magnification system, with the remaining differences attributed primarily to practical optical aberrations and alignment tolerances. The calibrated dual-view imaging platform provides the spatial resolution and quantitative accuracy required for absorption imaging of ultracold sodium atoms and establishes the experimental foundation for future investigations of sodium magneto-optical traps, Bose–Einstein condensation, and coherent spin dynamics in spinor sodium gases.
We introduce a novel, non-invasive imaging technique based on spin-dependent off-axis holography (SOAH) for spin-1 Bose-Einstein condensates (BECs). Utilizing a dual reference beam strategy, this method records two orthogonal circular polarization components of a single probe beam. The circular birefringence of spin-polarized atoms induces differing complex phase shifts in the polarization components of the light, which are reconstructed from the interference patterns captured on camera. Our approach enables spin- and density-resolved imaging of both phase and amplitude information \emph{in-situ} on a sub-millisecond time scale with minimal disturbance to the condensate. We explore the technique's efficacy under various background static fields, demonstrating its sensitivity to the quantization axis of the atoms and confirming its effectiveness.
This thesis details the development of a new ultracold atom experiment hosting (bosonic) ³⁹K, from the drawing board to its eventual utilisation in studying atom-light scattering in a uniform system of ultracold atoms with tunable interactions. This work is conceptually divided into three parts. The first part (Inferno), covering Chapters 1 - 3, establishes the theoretical framework for ultracold Bose gases and details the design philosophy and construction of the machine at the heart of this work. The primary benchmarks of the experiment include the production of harmonically trapped condensates of up to 1.2×10⁶ atoms in ≈ 12 s, uniform 3D degenerate gases of 0.8×10⁶ atoms in ≈ 14 s, and uniform 2D systems of 1.5×10⁵ atoms in ≈ 20 s. The second part (Purgatorio), covering Chapters 4 and 5, builds upon the machine's established capabilities. First, we detail the process by which we generate a uniform condensate used for our atom-light scattering experiments. Second, we demonstrate an alternative, all-optical route to quantum degeneracy that bypasses the usage of a magnetic trap in the sequence which is a central component of conventional methods (such as the one in Chapter 3). This technique is an intermediate step between sub-Doppler cooling and optical dipole trap (ODT) loading, designed to optimise the initial conditions for optical evaporation in the ODT. In particular, our method uses the simultaneous compression and cooling of a sub-Doppler cloud within a dynamically tunable blue-detuned tube trap, thereby enhancing the atom loading fraction into the ODT, where the final evaporation towards degeneracy occurs. The improvement of the initial conditions is the critical step that allows this all-optical sequence to successfully reach quantum degeneracy. The third and final part (Paradiso), covering Chapter 6, presents the main scientific result of this thesis. Here, we study the scattering between off-resonant light and a uniform Bose gas with tunable interactions, and illustrate the extreme sensitivity of atom-light scattering to local atomic correlations. We begin by showing that for the (quasi-)ideal (non-interacting) gas, the observed enhancement in atom-light scattering is captured by quantum statistical effects. This picture changes dramatically however, once we introduce atomic interactions. We find that due to the presence of local correlation effects, even weak repulsive interactions can completely suppress the enhancement in atom-light scattering, while attractive ones increase it above the ideal-gas level. Moreover, by studying the dynamics after an interaction quench, we show that the post-quench correlation dynamics are orders of magnitude faster than the dynamics associated with changes to momentum-space occupations or the density distribution. Our results thus establish off-resonant light scattering as a powerful and sensitive probe of equilibrium and non-equilibrium many-body physics.