This week we had the pleasure of welcoming Dr. Philipp Preiss from the University of Heidelberg who gave a talk on “Precursor of the Higgs Mode in Ultracold Few-Fermion Systems”. The abstract can be read below.

Precursor of the Higgs Mode in Ultracold Few-Fermion Systems

The emergence of collective modes from single-particle excitations is one of the most striking features of strongly interacting systems. Understanding such excitations is an ongoing challenge in nuclear physics, strongly correlated electron systems, and high-energy physics. Ultracold atoms in optical potentials provide a unique setting to precisely study the appearance of collective excitations in a tunable laboratory setting.

Here we experimentally observe the “birth” of a collective mode in a few-body system of ultracold Fermions. Using optical tweezers, we deterministically prepare few Fermions in the ground state of a two dimensional trap. This system exhibits a shell structure of stable “magic” numbers of 2,6,12… particles. We perform many-body spectroscopy through a modulation of the interaction strength find both single-particle and two-particle excitations. The latter consists of pairwise excitations akin to Cooper pairs and can be identified as the precursor of the Higgs mode in a two-dimensional Fermi gas.

In the future, we will probe such mesoscopic Fermi systems with single-particle detection. We recently demonstrated spin-resolved fluorescence imaging of individual atoms in free space, which will allow us to detect the momenta of every particle in the system in time-of-flight. We expect to directly see the formation of Cooper pairs and the momentum space signature of the BEC-BCS crossover.