A microscopic view of fermionic quantum matter with long-range interactions

Project Information

LongRangeFermi

Grant agreement ID: 101019739

DOI

10.3030/101019739

EC signature date 3 May 2021

Start date 1 October 2021

End date 30 June 2027

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 2 496 420,00

EU contribution

€ 2 496 420,00

Coordinated by

UNIVERSITY OF STUTTGART
Germany

Periodic Reporting for period 3 - LongRangeFermi (A microscopic view of fermionic quantum matter with long-range interactions)

Reporting period: 2024-10-01 to 2026-03-31

Summary of the context and overall objectives of the project

Strongly interacting Fermi gases appear in nature from the smallest to the largest scales — from atomic nuclei to white dwarfs and neutron stars. However, they are notoriously difficult to model and understand theoretically. Emulating such Fermi systems with ultracold atoms has been highly successful in recent years, but the approach has been limited to short-range interactions of the van der Waals type. The central goal of the proposed project is to gain microscopic understanding of fermionic quantum matter beyond local interactions — from dipolar to charged Fermi polarons. We will tackle these challenging fundamental physics problems experimentally with two innovative quantum gas microscopy techniques suited for the detection of strong dipolar quantum correlations in lattices and bilayers, and fermionic correlations around impurities and charges. The first technique is based on non-linear optical microscopy to study dipolar fermions on lattices and bilayers. The second technique is a newly developed and demonstrated pulsed ion microscope with unprecedented spatial (<200 nm) and temporal (<10 ns) resolution at 100 μm depth of field that will be extended to study impurities created in a bulk Fermi gas. The pulsed operation enables controlled studies of transport of charged polarons in a Fermi gas. This novel quantum gas microscope can resolve the dynamics from the two-body collisional time scale to the collective many-body timescale. With these versatile tools at hand, we will gain a deep microscopic understanding of the underlying physics of strongly correlated fermionic quantum matter with interactions longer-ranged than those typically present in all previous experiments. These highly controllable atomic model systems promise to guide research on related Fermi systems in material science, nuclear physics, and astrophysics.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

• The proposed work packages (WP) for the period are WP1 with the goal of developing a super resolution quantum gas microscope (QGM) for dysprosium atoms as well as WP4 aimed at creating a degenerate Fermi gas of lithium atoms under the pulsed ion microscope.
• WP1: An ultra-high vacuum setup as well as an accompanying laser system was constructed, which is used for trapping and laser cooling of dysprosium atoms. Up to 10^9 162Dy atoms are trapped in a five-beam magneto-optical trap (MOT) at temperatures of about 20 µK. The atoms are then loaded into a crossed beam optical dipole trap. The next step will be to evaporatively cool the atoms into quantum degeneracy. A setup for transporting the atoms from the ‘main’ chamber, where the MOT is created, to a separate ‘science’ chamber, where the QGM will be implemented, was tested and characterized. Furthermore, a setup for the active magnetic field stabilization to achieve the necessary stability for the super resolution scheme was developed. The science chamber, a custom very high numerical aperture in-vacuum objective (NA=0.9) as well as the specific trap geometry for the quantum gas microscope were designed and all necessary components will be ordered soon. As we are very sensitive to stray as well as scattered light, dedicated measures were developed to minimize the detrimental influence on any trap geometry. These measures include special coatings on optical surfaces, the geometry of the chamber itself as well as planning for a small hole in the center of the objective. A detailed simulation of the full imaging scheme including all relevant noise sources was performed, which confirmed the expected super resolution capabilities of the scheme as well as allowed us to developed suitable image analysis methods to be used with the QGM.
• WP4: The ion microscope was tested with bosonic rubidium atoms and the proven working principle will be extended to the Fermi gas of lithium atoms. Within the WP4, our existing setup needs to be upgraded in two broad aspects, which are
o Design and test of a dual species beam source for rubidium and lithium atoms.
o Setting up of the lasers for cooling and Rydberg excitation of lithium atoms.
We have designed a dual species effusive atomic oven based on the mixing chamber design, where both the atomic species effuse out towards the dual species Zeeman slower via a common exit aperture. We are currently in the process of assembling the different vacuum components and testing the performance of the oven design in a test setup. Keeping in mind the challenges of operating the atomic reservoirs at two vastly different temperatures, we are also currently testing the performance of atomic dispensers for lithium. These dispensers, when tested and integrated, are a promising direction towards making the atomic beam source compact. The lasers for the cooling and Rydberg excitation of lithium were purchased, delivered and tested. We have planned an optical setup for implementing the laser cooling of Lithium atoms and the necessary optical elements have been ordered.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

• We will implement a super resolution quantum gas microscope for dysprosium atoms. After cooling the ensemble of dysprosium atoms to quantum degeneracy, we will load it into a UV lattice and image the atoms using the custom high numerical aperture (NA) optical microscope, while applying a shelving scheme to achieve super resolution performance. As the dipolar interactions scale as (1/r3), the short 180 nm lattice spacing will be essential to realize significant nearest-neighbor interactions, in order to reach the strongly correlated regime where all relevant energy scales (tunnel coupling, on-site interactions, nearest-neighbor interactions and temperature) are of a similar order. We will adapt the experimental setup to be capable of trapping and cooling fermionic isotopes of Dysprosium as well in order to study fermionic extended Hubbard models. We will implement a sub-wavelength optical barrier to construct a bilayer situation for fermionic dysprosium atoms, with an even smaller spatial separation (~30 nm). In this configuration, we can investigate strong long-range correlations and the emergence of an interlayer superfluid in a 2D bulk system, and ultimately pair super fluidity.

• Once we have achieved to create degenerate Fermi gas of lithium atoms under the pulsed ion microscope, we will start with the textbook example of the Pauli hole in the bulk Fermi gas and the Friedel oscillations of a non-interacting Fermi gas around a light-induced impurity, and then systematically study the effects of interactions. In a next step, we will replace this external and immobile impurity with a well-controlled but mobile single ionic charge. In this way, we can study the charged polaron formation dynamics in a Fermi sea, where the interaction length between an atom and a single ionic impurity can exceed several hundred nanometers. The observation of charged polaron formation will be accompanied by transport measurements, where the charged polaron can be dragged through the Fermi gas by a controlled electric field and can be observed on the time scale of its internal dynamics

Picture Experience Setup

Picture MOT

Picture LongRangeFermi