2024
Eleonora Lippi
Cs-133 atoms in a Li-6 Fermi sea for exploring polaron physics in the heavy impurity limit PhD Thesis
2024.
@phdthesis{Lippi2024b,
title = {Cs-133 atoms in a Li-6 Fermi sea for exploring polaron physics in the heavy impurity limit },
author = {Eleonora Lippi},
url = {http://www.ub.uni-heidelberg.de/archiv/35527},
doi = {10.11588/heidok.00035527},
year = {2024},
date = {2024-10-30},
abstract = {The thesis deals with the experimental study of dilute ultracold gases of Cs-133 atoms mixed with a degenerate Fermi Sea of Li-6 atoms. It focuses on the problem of the coupling of an impurity to a surrounding quantum bath, which can be described as a quasi-particle known as polaron. The large mass imbalance between the impurity (Cs) and the bath (Li) leads to unique many-body phenomena, but also poses significant experimental challenges for mixing the two species at ultracold temperature where Li is quantum degenerate. In this work, we realize a mixture of a degenerate Li Fermi Sea and a dilute thermal Cs gas by adopting a bichromatic trapping approach and implementing a tightly confining and movable single beam trap for Li at the Cs tune-out wavelength. This allows the sequential preparation of the Li Fermi Sea, which can be overlapped with Cs atoms in a controlled manner, compensating for the differential gravitational sag between the two species. To probe the Fermi-polaron scenario, an optical spectroscopic method based on two-photon Raman transitions between the two lowest Zeeman states of Cs is implemented. Guided by theoretical predictions of the polaron spectral function, ejection spectroscopy on Cs impurities is performed to map the polaron energy spectrum as a function of interaction strength near a Li-Cs Feshbach resonance at 890 G, which provides high tunability of the interspecies interactions. Limitations to this kind of experiments and strategies to overcome them are discussed, laying the groundwork for exploring polaron physics with heavy mass impurities.},
keywords = {},
pubstate = {published},
tppubtype = {phdthesis}
}
The thesis deals with the experimental study of dilute ultracold gases of Cs-133 atoms mixed with a degenerate Fermi Sea of Li-6 atoms. It focuses on the problem of the coupling of an impurity to a surrounding quantum bath, which can be described as a quasi-particle known as polaron. The large mass imbalance between the impurity (Cs) and the bath (Li) leads to unique many-body phenomena, but also poses significant experimental challenges for mixing the two species at ultracold temperature where Li is quantum degenerate. In this work, we realize a mixture of a degenerate Li Fermi Sea and a dilute thermal Cs gas by adopting a bichromatic trapping approach and implementing a tightly confining and movable single beam trap for Li at the Cs tune-out wavelength. This allows the sequential preparation of the Li Fermi Sea, which can be overlapped with Cs atoms in a controlled manner, compensating for the differential gravitational sag between the two species. To probe the Fermi-polaron scenario, an optical spectroscopic method based on two-photon Raman transitions between the two lowest Zeeman states of Cs is implemented. Guided by theoretical predictions of the polaron spectral function, ejection spectroscopy on Cs impurities is performed to map the polaron energy spectrum as a function of interaction strength near a Li-Cs Feshbach resonance at 890 G, which provides high tunability of the interspecies interactions. Limitations to this kind of experiments and strategies to overcome them are discussed, laying the groundwork for exploring polaron physics with heavy mass impurities.
2023
Karen Wadenpfuhl
Emergence of synchronisation in a driven-dissipative hot Rydberg vapour Masters Thesis
2023.
@mastersthesis{nokey,
title = {Emergence of synchronisation in a driven-dissipative hot Rydberg vapour},
author = {Karen Wadenpfuhl},
url = {https://www.physi.uni-heidelberg.de/Publications/MThesis_KarenWadenpfuhl.pdf},
year = {2023},
date = {2023-09-15},
urldate = {2023-09-15},
keywords = {},
pubstate = {published},
tppubtype = {mastersthesis}
}
2022
Binh Tran
From Efimov Physics to Polarons in an Ultracold Mixture of Li and Cs Atoms PhD Thesis
2022.
@phdthesis{nokey,
title = {From Efimov Physics to Polarons in an Ultracold Mixture of Li and Cs Atoms},
author = {Binh Tran},
url = {https://archiv.ub.uni-heidelberg.de/volltextserver/31882/, heiDOK},
year = {2022},
date = {2022-06-30},
abstract = {This thesis reports on the reconstruction and improvement of a quantum gas experiment for studying Bose polarons as well as on theoretical investigations at the interface between Efimov physics and Fermi polarons. In both experiment and theory an ultracold mixture of fermionic 6Li and bosonic 133Cs with a large mass ratio is considered. With the improved experimental setup we realize Bose-Einstein condensates (BEC) of 133Cs with N = 10^4 atoms and molecular BECs of 6Li2 with N = 10^5 dimers. For the creation of Bose polarons we trap a small number of Li atoms in a tightly confined optical dipole trap and propose a scheme to combine them with the 133Cs BEC. In a theoretical study, employing the Born-Oppenheimer approximation, we calculate Efimov bound state energies (E < 0) in a three body Cs-Cs-Li system and in a many-body environment where two 133Cs atoms are immersed in a Fermi sea of 6Li atoms. In these systems the intraspecies scattering length determine the ground state and the Fermi sea leads to a modification of the binding energies. For the scattering states (E > 0) we calculate the induced scattering length between two 133Cs atoms mediated by the Fermi sea, and find resonant behavior. We find that for large mass ratios bound states can persist at positive energies to form quasibound states.},
keywords = {},
pubstate = {published},
tppubtype = {phdthesis}
}
This thesis reports on the reconstruction and improvement of a quantum gas experiment for studying Bose polarons as well as on theoretical investigations at the interface between Efimov physics and Fermi polarons. In both experiment and theory an ultracold mixture of fermionic 6Li and bosonic 133Cs with a large mass ratio is considered. With the improved experimental setup we realize Bose-Einstein condensates (BEC) of 133Cs with N = 10^4 atoms and molecular BECs of 6Li2 with N = 10^5 dimers. For the creation of Bose polarons we trap a small number of Li atoms in a tightly confined optical dipole trap and propose a scheme to combine them with the 133Cs BEC. In a theoretical study, employing the Born-Oppenheimer approximation, we calculate Efimov bound state energies (E < 0) in a three body Cs-Cs-Li system and in a many-body environment where two 133Cs atoms are immersed in a Fermi sea of 6Li atoms. In these systems the intraspecies scattering length determine the ground state and the Fermi sea leads to a modification of the binding energies. For the scattering states (E > 0) we calculate the induced scattering length between two 133Cs atoms mediated by the Fermi sea, and find resonant behavior. We find that for large mass ratios bound states can persist at positive energies to form quasibound states.
Saba Zia Hassan
Dynamics of anions and ultracold atoms in a hybrid atom-ion trap PhD Thesis
2022.
@phdthesis{nokey,
title = {Dynamics of anions and ultracold atoms in a hybrid atom-ion trap},
author = {Saba Zia Hassan},
url = {https://archiv.ub.uni-heidelberg.de/volltextserver/31692/, heiDOK},
year = {2022},
date = {2022-05-24},
urldate = {2022-05-24},
abstract = {In this work, the dynamics of anion-neutral interactions are studied in a hybrid atom-ion trap. An octupole radio-frequency trap is used for trapping anions, and a dark spontaneous-force optical trap is employed to create ultracold rubidium (Rb) atoms. Spatial density distributions of the ion and atom clouds are determined via photodetachment tomography and saturation absorption imaging, respectively. A method to map the ions’ translational temperature onto their time of flight to the detector is presented. This technique is applied to determine the temperature of OH−anions as they undergo laser-induced forced evaporative cooling to temperatures below 4 K. The dynamics of associative electronic detachment reaction between closed-shell anions OH−and alkali atoms are investigated where for a ground-state Rb the influence of a dipole-bound state as a reaction intermediate is observed. The interaction dynamics of Rb with OH−(H2O) are also explored, where a smaller atom-to-ion mass ratio favors sympathetic cooling via elastic collisions. For atomic O−, the detachment processes involving ground-state Rb are found to be closed and efficient anion sympathetic cooling, via ultracold Rb, is observed. These results present hybrid systems as a platform to investigate anion-neutral collision dynamics, particularly interesting for astrochemistry, fundamental physics, and quantum chemistry.},
keywords = {},
pubstate = {published},
tppubtype = {phdthesis}
}
In this work, the dynamics of anion-neutral interactions are studied in a hybrid atom-ion trap. An octupole radio-frequency trap is used for trapping anions, and a dark spontaneous-force optical trap is employed to create ultracold rubidium (Rb) atoms. Spatial density distributions of the ion and atom clouds are determined via photodetachment tomography and saturation absorption imaging, respectively. A method to map the ions’ translational temperature onto their time of flight to the detector is presented. This technique is applied to determine the temperature of OH−anions as they undergo laser-induced forced evaporative cooling to temperatures below 4 K. The dynamics of associative electronic detachment reaction between closed-shell anions OH−and alkali atoms are investigated where for a ground-state Rb the influence of a dipole-bound state as a reaction intermediate is observed. The interaction dynamics of Rb with OH−(H2O) are also explored, where a smaller atom-to-ion mass ratio favors sympathetic cooling via elastic collisions. For atomic O−, the detachment processes involving ground-state Rb are found to be closed and efficient anion sympathetic cooling, via ultracold Rb, is observed. These results present hybrid systems as a platform to investigate anion-neutral collision dynamics, particularly interesting for astrochemistry, fundamental physics, and quantum chemistry.
Manuel Gerken
Exploring p-wave Feshbach Resonances in Ultracold Lithium and Lithium-Cesium Mixtures PhD Thesis
2022.
@phdthesis{nokey,
title = {Exploring p-wave Feshbach Resonances in Ultracold Lithium and Lithium-Cesium Mixtures},
author = {Manuel Gerken},
url = {https://archiv.ub.uni-heidelberg.de/volltextserver/31719/, heiDOK},
year = {2022},
date = {2022-05-18},
abstract = {This thesis reports on the exploration of p-wave Feshbach resonances in ultracold Li-6 and Li-6-Cs-133 gases where the pair rotation angular momentum is l=1. An improved experimental apparatus is presented, allowing atom loss spectroscopy with a magnetic field resolutions down to several milli-Gauss on three Li-6, and five Li-6-Cs-133 Feshbach resonances. A doublet structure is observed for the first time on three Li-6 p-wave Feshbach resonances. We assign the splittings to spin-spin interactions where the projection of the pair rotation angular momentum m_l splits the resonance into m_l=0 and |m_l|=1. For the first time we report on observation of spin-rotation interaction on three Li-6-Cs-133 p-wave Feshbach resonances. Here the pair-rotation couples to the atomic spins, leading to an additional splitting of the m_l=-1 and m_l=+1 projections. Via coupled channel calculations we determine the dimensionless spin rotation constant to be |gamma|=0.566(50)x10^(-3). With a simple model we show that the strength of spin-rotation coupling depends significantly on the short-range part of the electron wave functions, highlighting the potential of Feshbach resonances to provide precise information on electron and nuclear wave functions at short internuclear distance. In an additional exploratory study of losses close to a single component Fermi pwave, Feshbach resonance we find changes in qualitative loss behavior depending on the density and temperature of the gas. We separate two regimes depending on the dominance of either elastic or inelastic collisions showing three- or two-body loss behavior, respectively. Collisional losses with possible cooling efficiencies similar to classic evaporative cooling are predicted.},
keywords = {},
pubstate = {published},
tppubtype = {phdthesis}
}
This thesis reports on the exploration of p-wave Feshbach resonances in ultracold Li-6 and Li-6-Cs-133 gases where the pair rotation angular momentum is l=1. An improved experimental apparatus is presented, allowing atom loss spectroscopy with a magnetic field resolutions down to several milli-Gauss on three Li-6, and five Li-6-Cs-133 Feshbach resonances. A doublet structure is observed for the first time on three Li-6 p-wave Feshbach resonances. We assign the splittings to spin-spin interactions where the projection of the pair rotation angular momentum m_l splits the resonance into m_l=0 and |m_l|=1. For the first time we report on observation of spin-rotation interaction on three Li-6-Cs-133 p-wave Feshbach resonances. Here the pair-rotation couples to the atomic spins, leading to an additional splitting of the m_l=-1 and m_l=+1 projections. Via coupled channel calculations we determine the dimensionless spin rotation constant to be |gamma|=0.566(50)x10^(-3). With a simple model we show that the strength of spin-rotation coupling depends significantly on the short-range part of the electron wave functions, highlighting the potential of Feshbach resonances to provide precise information on electron and nuclear wave functions at short internuclear distance. In an additional exploratory study of losses close to a single component Fermi pwave, Feshbach resonance we find changes in qualitative loss behavior depending on the density and temperature of the gas. We separate two regimes depending on the dominance of either elastic or inelastic collisions showing three- or two-body loss behavior, respectively. Collisional losses with possible cooling efficiencies similar to classic evaporative cooling are predicted.
Renato Ferracini Alves
Realization of a Heisenberg XXZ spin system using Rydberg atoms PhD Thesis
2022.
@phdthesis{,
title = {Realization of a Heisenberg XXZ spin system using Rydberg atoms},
author = {Renato Ferracini Alves },
url = {https://archiv.ub.uni-heidelberg.de/volltextserver/31511/, heiDOK},
year = {2022},
date = {2022-02-02},
urldate = {2022-02-02},
abstract = {In this thesis, we present the realization of an isolated Heisenberg XXZ spin 1/2 system with an off-diagonal disorder in the coupling constants using cold atoms in highly excited Rydberg states. We select a set of Rydberg states that interact via van der Waals interaction which can be mapped onto an interacting spin system. We investigate the out-of-equilibrium dynamics of the spin system after it has been initialized in a fully magnetized state. Following unitary evolution governed by the Heisenberg spin Hamiltonian, we measure the magnetization as a function of the evolution time. By fitting a stretched exponential function to the resulting magnetization dynamics be obtain a stretched exponent of β = 0.32 revealing a slow relaxation of the spin system, similar to what is found in spin glasses. By choice, the initial state is an eigenstate of the mean-field Hamiltonian and thus the observed relaxation indicates that the dynamics are triggered by quantum fluctuations. We find that varying the distribution of coupling constants by means of the so-called dipole blockade effect has no impact on the stretching exponent indicating that it is a universal parameter of the system independent of the microscopic details for the range of disorder explored in the experiment. It also allows us to combine the different datasets by re-scaling the time domain with the characteristic interaction strength. The combined datasets expand our measurements to two orders of magnitude in the re-scaled time-domain showing that slow dynamics is a persistent effect for long evolution times.},
keywords = {},
pubstate = {published},
tppubtype = {phdthesis}
}
In this thesis, we present the realization of an isolated Heisenberg XXZ spin 1/2 system with an off-diagonal disorder in the coupling constants using cold atoms in highly excited Rydberg states. We select a set of Rydberg states that interact via van der Waals interaction which can be mapped onto an interacting spin system. We investigate the out-of-equilibrium dynamics of the spin system after it has been initialized in a fully magnetized state. Following unitary evolution governed by the Heisenberg spin Hamiltonian, we measure the magnetization as a function of the evolution time. By fitting a stretched exponential function to the resulting magnetization dynamics be obtain a stretched exponent of β = 0.32 revealing a slow relaxation of the spin system, similar to what is found in spin glasses. By choice, the initial state is an eigenstate of the mean-field Hamiltonian and thus the observed relaxation indicates that the dynamics are triggered by quantum fluctuations. We find that varying the distribution of coupling constants by means of the so-called dipole blockade effect has no impact on the stretching exponent indicating that it is a universal parameter of the system independent of the microscopic details for the range of disorder explored in the experiment. It also allows us to combine the different datasets by re-scaling the time domain with the characteristic interaction strength. The combined datasets expand our measurements to two orders of magnitude in the re-scaled time-domain showing that slow dynamics is a persistent effect for long evolution times.
2021
Annika Tebben
2021.
@phdthesis{nokey,
title = {Rydberg Electromagnetically Induced Transparency - A vanishing linear response, resonances, and a stationary Rydberg polariton},
author = {Annika Tebben},
url = {https://archiv.ub.uni-heidelberg.de/volltextserver/30661/, heiDOK},
year = {2021},
date = {2021-10-22},
urldate = {2021-10-22},
abstract = {Rydberg electromagnetically induced transparency (Rydberg EIT) enables extremely strong optical nonlinearities, opening the possibility for photon-photon interactions and exotic states of light. Subjects of this thesis are the development and the experimental test of semiclassical models for Rydberg EIT systems on two-photon resonance. Beyond that, this thesis opens the route towards enhanced photon-photon interactions in terms of an increased interaction time. Three major results are achieved: (i) In the semiclassical regime, we extend existing models and reveal that a two-body, two-photon resonance leads to an enhanced nonlinear optical response. (ii) We develop an experimental method to rigorously test semiclassical models of Rydberg EIT. For this purpose, we go beyond previous experimental investigations and measure transmission spectra on two-photon resonance, where the linear response of the system vanishes. We identify qualitative differences between a measured absorption feature and predictions provided by a mean-field model, a Monte-Carlo rate equation simulation, and a theory based on a pairwise treatment of atomic interactions. (iii) In the quantum regime, we propose and analyze a novel scheme to endow a stationary light polariton with a Rydberg character, resulting in a stationary Rydberg polariton. Our scheme offers the prospect for polariton interactions with increased interaction time, and thus might find application in the creation of exotic states of light.},
keywords = {},
pubstate = {published},
tppubtype = {phdthesis}
}
Rydberg electromagnetically induced transparency (Rydberg EIT) enables extremely strong optical nonlinearities, opening the possibility for photon-photon interactions and exotic states of light. Subjects of this thesis are the development and the experimental test of semiclassical models for Rydberg EIT systems on two-photon resonance. Beyond that, this thesis opens the route towards enhanced photon-photon interactions in terms of an increased interaction time. Three major results are achieved: (i) In the semiclassical regime, we extend existing models and reveal that a two-body, two-photon resonance leads to an enhanced nonlinear optical response. (ii) We develop an experimental method to rigorously test semiclassical models of Rydberg EIT. For this purpose, we go beyond previous experimental investigations and measure transmission spectra on two-photon resonance, where the linear response of the system vanishes. We identify qualitative differences between a measured absorption feature and predictions provided by a mean-field model, a Monte-Carlo rate equation simulation, and a theory based on a pairwise treatment of atomic interactions. (iii) In the quantum regime, we propose and analyze a novel scheme to endow a stationary light polariton with a Rydberg character, resulting in a stationary Rydberg polariton. Our scheme offers the prospect for polariton interactions with increased interaction time, and thus might find application in the creation of exotic states of light.
Jonas Tauch
New approaches for cooling molecular anions to the Kelvin range PhD Thesis
2021.
@phdthesis{nokey,
title = {New approaches for cooling molecular anions to the Kelvin range},
author = {Jonas Tauch},
url = {https://archiv.ub.uni-heidelberg.de/volltextserver/30105/, heiDOK},
year = {2021},
date = {2021-06-02},
abstract = {This thesis presents two anion cooling techniques based on their interaction with photons or ultracold atoms, pushing the frontier of anion cooling beyond state-of-the-art experiments. A hybrid atom-ion trap (HAITrap) is presented, combining an octupole radio frequency (rf) trap and a dark spontaneous-force optical trap for rubidium. The anions and atoms are probed via photodetachment tomography, time-of-flight thermometry and saturation absorption imaging, respectively. The anion photodetachment via a focused far-threshold laser beam removes anions selectively by their energy. This thesis reports forced evaporative cooling of OH− via dynamically moving the beam, below 4 Kelvin in 2 seconds. A derived thermodynamic model describes the evolution of anion temperature and number, including the importance of ion-ion thermalization and resulting rf-heating in such traps. It shows experimental and theoretical framework to prepare any anionic specie in a vast energy range. This thesis also reports the sympathetic cooling and the collision dynamics of anions with ultracold rubidium in a HAITrap. The cooling is experimentally demonstrated to 30(2) Kelvin for O− and 135(8) Kelvin for OH−. The different cooling behavior is explained by their dissimilar loss channels, which are identified and quantified. These limitations can be overcome in future experiments, providing a tool to cool anions translationally and internally.},
keywords = {},
pubstate = {published},
tppubtype = {phdthesis}
}
This thesis presents two anion cooling techniques based on their interaction with photons or ultracold atoms, pushing the frontier of anion cooling beyond state-of-the-art experiments. A hybrid atom-ion trap (HAITrap) is presented, combining an octupole radio frequency (rf) trap and a dark spontaneous-force optical trap for rubidium. The anions and atoms are probed via photodetachment tomography, time-of-flight thermometry and saturation absorption imaging, respectively. The anion photodetachment via a focused far-threshold laser beam removes anions selectively by their energy. This thesis reports forced evaporative cooling of OH− via dynamically moving the beam, below 4 Kelvin in 2 seconds. A derived thermodynamic model describes the evolution of anion temperature and number, including the importance of ion-ion thermalization and resulting rf-heating in such traps. It shows experimental and theoretical framework to prepare any anionic specie in a vast energy range. This thesis also reports the sympathetic cooling and the collision dynamics of anions with ultracold rubidium in a HAITrap. The cooling is experimentally demonstrated to 30(2) Kelvin for O− and 135(8) Kelvin for OH−. The different cooling behavior is explained by their dissimilar loss channels, which are identified and quantified. These limitations can be overcome in future experiments, providing a tool to cool anions translationally and internally.
Tobias Martin Wintermantel
Complex systems dynamics in laser excited ensembles of Rydberg atoms PhD Thesis
2021.
@phdthesis{nokey,
title = {Complex systems dynamics in laser excited ensembles of Rydberg atoms},
author = {Tobias Martin Wintermantel},
url = {https://archiv.ub.uni-heidelberg.de/volltextserver/29303/, heiDOK},
year = {2021},
date = {2021-01-13},
abstract = {In this thesis I present experimental and theoretical results showing that an ultracold gas under laser excitation to Rydberg states offers a controllable platform for studying the interesting complex dynamics that can emerge in driven-dissipative systems. The findings can be summarized according to the following three main insights: (i) The discovery of self-organized criticality (SOC) in our Rydberg system under facilitated excitation via three signatures: self-organization of the density to a stationary state; scale invariant behavior; and a critical response in terms of power-law distributed excitation avalanches. Additionally, we explore a mechanism inherent to our system which stabilizes the SOC state. We further investigate this stabilization via a controlled, variable driving of the system. These analyses can help answer the question of why scale invariant behavior is so prevalent in nature. (ii) A striking connection between the power-law growth of the Rydberg excitation number and epidemic spreading is found. Based on this, an epidemic network model is devised which efficiently describes the collective excitation dynamics. The importance of heterogeneity in the emergent Rydberg network and associated Griffiths effects provide a way to explain the observation of non-universal power laws. (iii) A novel quantum cellular automata implementation is proposed using atomic arrays together with multifrequency laser fields. This provides a natural framework to study the relation between microscopic processes and global dynamics, where special rules are found to generate entangled states with applications in quantum metrology and computing.},
keywords = {},
pubstate = {published},
tppubtype = {phdthesis}
}
In this thesis I present experimental and theoretical results showing that an ultracold gas under laser excitation to Rydberg states offers a controllable platform for studying the interesting complex dynamics that can emerge in driven-dissipative systems. The findings can be summarized according to the following three main insights: (i) The discovery of self-organized criticality (SOC) in our Rydberg system under facilitated excitation via three signatures: self-organization of the density to a stationary state; scale invariant behavior; and a critical response in terms of power-law distributed excitation avalanches. Additionally, we explore a mechanism inherent to our system which stabilizes the SOC state. We further investigate this stabilization via a controlled, variable driving of the system. These analyses can help answer the question of why scale invariant behavior is so prevalent in nature. (ii) A striking connection between the power-law growth of the Rydberg excitation number and epidemic spreading is found. Based on this, an epidemic network model is devised which efficiently describes the collective excitation dynamics. The importance of heterogeneity in the emergent Rydberg network and associated Griffiths effects provide a way to explain the observation of non-universal power laws. (iii) A novel quantum cellular automata implementation is proposed using atomic arrays together with multifrequency laser fields. This provides a natural framework to study the relation between microscopic processes and global dynamics, where special rules are found to generate entangled states with applications in quantum metrology and computing.