Unveiling the superfluid and solid behaviour in dipolar supersolids

@article{PoliPhD,
  title = {Unveiling the superfluid and solid behaviour in dipolar supersolids},
  author = {Elena Poli},
  journal = {PhD Thesis},
  year = {2025},
  month = {Sep},
  abstract = {Ultracold atomic gases offer a highly controllable platform for studying fundamental
properties of quantum matter. Since the first realization of Bose-Einstein condensation,
the field has progressed rapidly, enabling increasingly sophisticated experiments
aimed at deepening our understanding of quantum matter under controllable conditions.
Among the atomic species brought to quantum degeneracy, highly magnetic atoms such
as chromium, erbium, and dysprosium have opened new directions for research. Their
large magnetic dipole moments introduce long-range and anisotropic dipolar interactions,
which, in competition with short-range contact interactions, give rise to a rich
landscape of many-body phenomena. A particularly exciting development is the possibility
to access supersolid phase of matter, which uniquely combine superfluid and
crystalline properties–two properties typically considered mutually exclusive.
This thesis presents a theoretical study of two-dimensional dipolar supersolids, with
a focus on the characterization of their solid and superfluid properties. Using extensive
numerical simulations, we identify the key control parameters that enabled the first
experimental observation of the transition from one-dimensional to two-dimensional
supersolidity. We further study the formation dynamics of the supersolid states and
characterize the excitation spectrum to determine the nature of the gapless modes, each
associated with a spontaneously broken symmetry. Within a hydrodynamic framework,
we extract sound velocities and elastic parameters, including the shear modulus, which
serves as signature of solid behaviour.
The superfluid nature is explored via studies of the system’s rotational dynamics.
We first focus on collective angular oscillations, known as the scissor mode, and assess
whether the frequency of this mode provides information about the superfluid fraction.
We then explore a different regime by implementing full rotations through magnetic field
stirring. This protocol enables the nucleation of quantized vortices, topological defects
manifesting as phase singularities. These are one of the most distinctive manifestation
of superfluid nature. These studies led to the first experimental observations of vortices
in rotating dipolar supersolids.
Finally, the results of this thesis are extended to propose a novel application of dipolar
supersolids as quantum analogues of the inner crust of neutron stars. We develop a
model to simulate glitches, sudden spin-up events usually observed in pulsars, via vortex
unpinning mechanisms. We show how dipolar supersolids provide a unique opportunity
to study both vortex and crystal dynamics during such events, which remain inaccessible
through direct astrophysical observation. This work marks the first concrete application
of supersolids to large scale systems, like neutron stars, and an important step towards
quantum simulations of stellar objects from Earth.},
  url = {https://www.erbium.at/FF/wp-content/uploads/2025/09/PhDthesis_Poli.pdf},
}