Browsing by Author "Lech, Alex"

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    Patterns in Interacting Quantum Gases
    (2021-11-19) Bekassy, Viktor; Heuts, Olivia; Lech, Alex; Lundqvist, Carin; Magnusson, Erik; University of Gothenburg/Department of physics; Göteborgs universitet/Institutionen för fysik
    Quantum gases is a novel field of experimental research, where it is possible to study the universal behaviour of quantum particles under controlled circumstances. In two experiments by Zürn et al. and Holten et al., patterns such as paring effects, magic numbers and Pauli crystals have emerged in a quantum gas consisting of a few ultracold 6Li atoms confined in an optical trap. By modelling these experiments and using the universal behaviour of quantum particles, we can achieve a greater understanding of how the building blocks of our universe behave and then apply that knowledge to more complicated systems, such as neutron stars or the atomic nucleus. This thesis aims to model the mentioned experiments as a few interacting fermions in a harmonic potential. By treating the interaction as a minor perturbation and calculating the energy of the system numerically with perturbation theory, we were able to compare our results with the experiments by Zürn et al. and found that they were in good agreement. Both showed a pronounced shell structure, resulting in magic numbers, and the emergence of pairing between fermions. Furthermore, the results were consistent with our analytically derived solution for two particles. Additionally, Pauli crystals in one and two dimensions were simulated using Matlab and the Metropolis algorithm, resulting in us successfully recreating the very recent experimental results by Holten et al.. Finally, interactions were added to Pauli crystals in 1D, showing new pairing patterns and opening up for further research.
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    Simulation of light-absorbing microparticles in an optical landscape
    (2024-06-10) Lech, Alex; University of Gothenburg/Department of Physics; Göteborgs universitet / Institutionen för fysik
    Simulating the dynamics of active particles play a key role in understanding the many behaviours active matter can exhibit. Experimental studies are more costly than simulations in this regard, as there is much work that needs to be performed with setups and observation time. Computer simulations are a powerful and costeffective supplements to experiments. One topic of study within active matter is light-absorbing microparticles which are commonly made of silica with a lightabsorbing metallic compound such as iron oxide or gold. One such microparticle is the Janus particle, a silica particle with a hemispherical coating of gold as the absorbing compound. When illuminated with a laser, the coating absorbs the light and heats up rapidly, generating a temperature gradient which allows the Janus particle to exhibit self-propulsion and clustering with other Janus particles due to thermophoresis and Brownian motion. In this thesis, I introduce a model which simulates light-absorbing microparticles with a desired distribution of iron oxide in an optical landscape. In particular, the case of an optical landscape characterized by a periodical sinusoidal intensity profile of a given spatial periodicity will be considered. The results show that for a hemispherical distribution (Janus particle) there is selfpropulsion originating at the side of the cap, with super-diffusive characteristics. When the laser periodicity is similar to the particle radius, it becomes confined between two high intensity peaks. A particle with uniform distribution diffuses with Brownian motion, with no self-propulsion. Clustering behaviour arises when multiple particles are in close proximity to each other, as observed in experiments. The agreement with experimental results opens up for the opportunity to simulate other light-absorbing particles with different distributions of absorbing compounds.