Speaker
Description
Ultracold quantum gases offer a highly tunable platform for exploring strongly interacting many-body systems. In highly imbalanced mixtures, we can explore the quantum behavior of impurities. Our investigation focuses on bosonic $^{41}$K impurities interacting with a Fermi sea of $^6$Li atoms, forming a system that can be described in terms of quasiparticles known as Fermi polarons. While previous studies have probed the static and dynamic features of such polarons using radio-frequency spectroscopy [1], understanding kinetic properties such as effective mass and dispersion relation can be accomplished by means of Raman spectroscopy [2]. Notably, Raman transitions do not only facilitate manipulation of the impurity's internal state but they also offer control over its momentum state. Utilizing a newly built Raman setup, we can transfer multiple photon momenta to the impurities in a controlled manner, enabling the investigation of polaron behavior with finite momentum within a Fermi sea. Here, we present our experimental results on the momentum-dependent polaron energy for different interaction strengths, highlighting the breakdown of the polaron picture at low momenta.
The figure shows the energy of the attractive Fermi polaron as a function of the transferred momentum. The low-momentum behavior is governed by the effective mass, while at high momenta the polaron gets "undressed" and the effective mass description breaks down.
[1] Fritsche et al., Phys. Rev. A 103, 053314 (2021)
[2] Ness et al., Phys. Rev. X 10, 041019 (2020)
