Abstract:

Ultracold atomic gases are exceptionally well suited to study the physics of strongly
interacting Fermi gases. Tunable interactions and engineered geometries have enabled
insights into the origin of fermionic pairing, superfluidity and collective excitations in normal
and degenerate Fermi gases. The next step in this endeavor will be to gain access to single-
particle observables for a microscopic comparison between experiment and theory.
I will present our recent development of such microscopic probes for few-body Fermi gases.
Using a free-space fluorescence imaging scheme for Lithium 6, we detect individual particles
after time-of flight and determine the spin and momentum of every particle in the system.
We apply this technique to few-fermion states in two dimensions, which we assemble
particle by particle. Even in the absence of interactions, we observe order enforced by the
Pauli exclusion principle [1]. Switching on attractive interactions between the particles
induces pair formation and momentum correlations. We find that even systems consisting
of only a dozen particles exhibit correlations and excitation spectra known from many-body
theory [2].
Our experiments provide a new avenue to systematically explore the emergence of
collective phenomena from the microscopic limit.

[1] M. Holten et al., Phys. Rev. Lett. 126, 020401 (2021)
[2] L. Bayha et al., Nature 587, 583 (2020)