Repulsive Fermi polarons and their induced interactions in binary mixtures of ultracold atoms

Abstract

We explore repulsive Fermi polarons in one-dimensional harmonically trapped few-body mixtures of ultracold atoms using as a case example a 6 Li-40 K mixture. A characterization of these quasiparticlelike states, whose appearance is signaled in the impurity's radiofrequency spectrum, is achieved by extracting their lifetime and residua. Increasing the number of 40 K impurities leads to the occurrence of both single and multiple polarons that are entangled with their environment. An interactiondependent broadening of the spectral lines is observed suggesting the presence of induced interactions. We propose the relative distance between the impurities as an adequate measure to detect induced interactions independently of the specifics of the atomic mixture, a result that we showcase by considering also a 6 Li-173 Yb system. This distance is further shown to be indicative of the generation of entanglement independently of the size of the bath ( 6 Li) and the atomic species of the impurity. The generation of entanglement and the importance of induced interactions are revealed with an emphasis on the regime of intermediate interaction strengths.

Many-body quantum dynamics and induced correlations of Bose polarons

“…In a corresponding experiment, this quench protocol can be implemented by using a radiofrequency π/2 pulse with an exposure time much smaller than ω −1 [19]. The pulse acts upon the spin degree of freedom of the impurity, which maps the pseudospin- impurities to the superposition state | The setup and processes addressed in our work can be experimentally realized utilizing radiofrequency spectroscopy [9,18,22,23,43] and Ramsey interferometry [18].…”

“…To capture the emerging effective interactions between the two bosonic impurities we monitor their relative distance [9,42] given by Here,N a with =   a , is the number operator that measures the number of bosons in the spin-a state. Experimentally, ( ) á ñ r t aa can be probed via in situ spin-resolved single-shot measurements on the spin-a state [91].…”

“…acts on the impurities just as an additional repulsive (g BI >0) or attractive (g BI <0) potential on top of the externally imposed parabolic trap. It is noteworthy that the simplification of the impurity problem provided by equation (9) neglects several phenomena that might be important for the description of the ground state of the impurity system. First, the renormalization of the impurity's mass,  m m I I eff by the coupling with its environment is neglected and, most importantly, the possible emergence of induced interactions is not contained in equation (9), due to the absence of two-body terms.…”

“…the polarons [1,2], which were originally introduced by Landau [3][4][5]. This dressing mechanism can strongly modify the elementary properties of the impurity atoms and lead to concepts such as effective mass and energy [6,7], induced interactions [8,9] and attractively bound bipolaron states [1,2,10,11]. Polaron states have been recently realized in ultracold atom experiments [12][13][14], which exhibit an unprecedented degree of controllability and, in particular, allow to adjust the interaction between the impurities and the medium with the aid of Feshbach resonances [15,16].…”

“…Experimentally Bose [20][21][22][23][24] and Fermi [12,13,17] polarons have been observed and these experiments confirmed the importance of higher-order correlations for the description of the polaronic properties. The experiments in turn have spurred additional several theoretical investigations which have aimed at describing different polaronic aspects [25,26] by operating e.g.within the Fröhlich model [27][28][29][30][31], effective Hamiltonian approximations [8,[32][33][34], variational approaches [7,9,22,[35][36][37], renormalization group methods [25,38,39] and the path integral formalism [40,41].…”