Ultracold Dipolar Erbium Atoms: From Scattering Phenomena to Quantum Simulations

by Simon Baier
Abstract:
Remarkable progress in the field of experimental quantum physics has enabled the preparation of quantum systems across various experimental platforms. The ability to precisely control and manipulate quantum states by experimental means, allows to study fundamental laws of quantum mechanics and their impact at the many-body level. Ultracold atomic gases are a powerful and flexible platform, providing precise control of key parameters, such as temperature, density, internal and external degrees of freedom, dimensionality, or the trapping geometry. With the access of controllable interparticle interaction, a plethora of fascinating quantum phenomena has been observed. While the field was pioneered along studies with short-range contact interaction, nowadays dipolar interactions, featuring a long-range and anisotropic character, are attracting a large attention within the community. This thesis reports on the investigation of quantum phenomena emerging from dipolar interactions. As a workhorse for our studies, we use ultracold gases of strongly magnetic erbium atoms. Erbium has first been Bose-Einstein condensed in 2012 in our laboratory. Shortly after, we created the first degenerate Fermi gas of erbium. This thesis focuses on the use of both systems as a resource to investigate dipolar quantum phenomena from the few- to the many-body level. With dipolar fermions, we unveil the universal character of ultracold dipolar scattering, enabling a unique path towards quantum degenerate identical fermions. We further observe a peculiar dependence of the total elastic scattering cross section on the dipole orientation. The few-body collisional physics also impacts the behavior of the system at the many-body level. Reporting on the first observation of a many-body effect in a dipolar Fermi gas, we demonstrate the deformation of the Fermi surface. With bosonic particles, we investigate the origin of a strong level repulsion in Feshbach spectra of magnetic lanthanides and trace it back to the anisotropic van der Waals interaction among the atoms. Utilizing Feshbach resonances, we report on the first production of dipolar Feshbach molecules and reveal a universal behavior of the stabilization of inelastic losses in reduced dimensions by dipolar interactions. As a major step towards strongly correlated dipolar systems, we investigate the system’s behavior in a three-dimensional optical lattice. In particular, we report on the realization of extended Hubbard models with dipolar bosonic and fermionic atoms. In bosonic systems, we directly observe nearest-neighbor interactions activated by the long-range dipolar interaction. We demonstrate the strengthening or weakening of the Mott insulator quantum many-body phase via solely changing the dipole orientation. For the fermionic counterpart, we add the spin-degree of freedom, giving rise to a large spin-19/2 system. A lattice protection technique allows to investigate in detail the elastic collisional properties of a two-state mixture. With our method, we realize for the first time a strongly interacting dipolar Fermi gas. The successful preparation of extended spinor Fermi Hubbard systems brings exciting prospects for future investigations at the interface with solid state physics. Offsite terms emerging from dipolar interactions give rise to clustered states, exotic lattice spin models, resonant demagnetization dynamics, or exotic quantum phases.
Reference:
Ultracold Dipolar Erbium Atoms: From Scattering Phenomena to Quantum Simulations,
Simon Baier,
PhD Thesis, 2018.
Bibtex Entry:
@article{BaierPhD,
  title = {Ultracold Dipolar Erbium Atoms: From Scattering Phenomena to Quantum Simulations},
  author = {Baier, Simon},
  journal = {PhD Thesis},
  year = {2018},
  month = {Oct},
  abstract = {Remarkable progress in the field of experimental quantum physics has enabled the preparation
of quantum systems across various experimental platforms. The ability to precisely
control and manipulate quantum states by experimental means, allows to study fundamental
laws of quantum mechanics and their impact at the many-body level.
Ultracold atomic gases are a powerful and flexible platform, providing precise control of key
parameters, such as temperature, density, internal and external degrees of freedom, dimensionality,
or the trapping geometry. With the access of controllable interparticle interaction,
a plethora of fascinating quantum phenomena has been observed. While the field was pioneered
along studies with short-range contact interaction, nowadays dipolar interactions,
featuring a long-range and anisotropic character, are attracting a large attention within the
community.
This thesis reports on the investigation of quantum phenomena emerging from dipolar interactions.
As a workhorse for our studies, we use ultracold gases of strongly magnetic erbium
atoms. Erbium has first been Bose-Einstein condensed in 2012 in our laboratory. Shortly
after, we created the first degenerate Fermi gas of erbium. This thesis focuses on the use of
both systems as a resource to investigate dipolar quantum phenomena from the few- to the
many-body level.
With dipolar fermions, we unveil the universal character of ultracold dipolar scattering,
enabling a unique path towards quantum degenerate identical fermions. We further observe
a peculiar dependence of the total elastic scattering cross section on the dipole orientation.
The few-body collisional physics also impacts the behavior of the system at the many-body
level. Reporting on the first observation of a many-body effect in a dipolar Fermi gas, we
demonstrate the deformation of the Fermi surface. With bosonic particles, we investigate
the origin of a strong level repulsion in Feshbach spectra of magnetic lanthanides and trace
it back to the anisotropic van der Waals interaction among the atoms. Utilizing Feshbach
resonances, we report on the first production of dipolar Feshbach molecules and reveal a
universal behavior of the stabilization of inelastic losses in reduced dimensions by dipolar
interactions.
As a major step towards strongly correlated dipolar systems, we investigate the system’s
behavior in a three-dimensional optical lattice. In particular, we report on the realization of
extended Hubbard models with dipolar bosonic and fermionic atoms. In bosonic systems, we
directly observe nearest-neighbor interactions activated by the long-range dipolar interaction.
We demonstrate the strengthening or weakening of the Mott insulator quantum many-body
phase via solely changing the dipole orientation. For the fermionic counterpart, we add the
spin-degree of freedom, giving rise to a large spin-19/2 system. A lattice protection technique
allows to investigate in detail the elastic collisional properties of a two-state mixture. With
our method, we realize for the first time a strongly interacting dipolar Fermi gas.
The successful preparation of extended spinor Fermi Hubbard systems brings exciting
prospects for future investigations at the interface with solid state physics. Offsite terms
emerging from dipolar interactions give rise to clustered states, exotic lattice spin models,
resonant demagnetization dynamics, or exotic quantum phases.},
  url = {http://www.erbium.at/FF/wp-content/uploads/2018/10/Dissertation_Simon_Baier.pdf},
}