We characterize properties of the so-called repulsive polaron across the recently discovered orbital Feshbach resonance in alkaline-earth(-like) atoms. Being a metastable quasiparticle excitation at the positive energy, the repulsive polaron is induced by the interaction between an impurity atom and a Fermi sea. By analyzing in detail the energy, the polaron residue, the effective mass, and the decay rate of the repulsive polaron, we reveal interesting features that are intimately related to the two-channel nature of the orbital Feshbach resonance. In particular, we find that the life time of the repulsive polaron is non-monotonic in the Zeeman-field detuning bewteen the two channels, and has a maximum on the BEC-side of the resonance. Further, by considering the stability of a mixture of the impurity and the majority atoms against phase separation, we show that the itinerant ferromagnetism may exist near the orbital Feshbach resonance at appropriate densities. Our results can be readily probed experimentally, and have interesting implications for the observation of itinerant ferromagnetism near an orbital Feshbach resonance.

We study the impurity problem in a Fermi gas of 173 Yb atoms near an orbital Feshbach resonance, where a single moving particle in the 3 P0 state interacting with two background Fermi seas of particles in different nuclear states of the ground 1 S0 manifold. By employing wave function ansatzs for molecule and polaron states, we investigate various properties of the molecule, the attractive polaron, and the repulsive polaron states. We find that in comparison to the case of only one Fermi sea is populated, the presence of an additional Fermi sea acts as an energy shift between the two channels of the orbital Feshbach resonance. Besides, the fluctuation around the Fermi level would also bring sizable effects to the attractive and repulsive polaron states.

We study the Fermi polaron problem of one mobile spin-up impurity immersed atop the bath consisting of spin-down fermions in one-and two-dimensional square lattices. We solve this problem by applying a variational approach with non-Gaussian states after separating the impurity and the background by the Lee-Low-Pines transformation. The ground state for a fixed total momentum can be obtained via imaginary time evolution for the variational parameters. For the one-dimensional case, the variational results are compared with numerical solutions of the matrix product state method with excellent agreement. In two-dimensional lattices, we focus on the dilute limit, and find a polaron-molecule evolution in consistence with previous results obtained by variational and quantum Monte Carlo methods for models in continuum space. Comparing to previous works, our method provides the lowest ground state energy in the entire parameter region considered, and has an apparent advantage as it does not need to assume in priori any specific form of the variational wave function.

We show that in two-band $s$-wave superfluids it is possible to induce quantum phase transitions (QPTs) by tuning intraband and interband $s$-wave interactions, in sharp contrast to single-band $s$-wave superfluids, where only a crossover between Bardeen-Cooper-Schrieffer (BCS) and Bose-Einstein condensation (BEC) superfluidity occurs. For non-zero interband and attractive intraband interactions, we demonstrate that the ground state has always two interpenetrating superfluids possessing three spectroscopically distinct regions where pairing is qualitatively different: (I) BCS pairing in both bands (BCS-BCS), (II) BCS pairing in one band and BEC pairing in the other (BCS-BEC), and (III) Bose pairing in both bands (BEC-BEC). Furthermore, we show that by fine tuning the interband interactions to zero one can induce QPTs in the ground state between three distinct superfluid phases. There are two phases where only one band is superfluid ($S_1$ or $S_2$), and one phase where both bands are superfluid $(S_1 + S_2)$, a situation which is absent in one-band $s$ wave systems. Lastly, we suggest that these crossovers and QPTs may be observed in multi-component systems such as $^{6}{\rm Li}$, $^{40}{\rm K}$, $^{87}{\rm Sr}$, and $^{173}{\rm Yb}$.

In recent years, alkaline-earth and alkaline-earth-like atoms have attracted much research interest in the field of ultracold atom. Especially, the recently discovered orbital Feshbach resonance makes it possible to investigate a strongly interacting gas of alkaline-earth or alkaline-earth-like atoms, which has greatly enriched the scope of quantum simulation in these systems. This paper focuses on the impurity problem in a Fermi gas of ¹⁷³Yb atoms near orbital Feshbach resonance. In this problem, the impurity atom in ³<i>P</i>₀ state will interact with the background Fermi sea in the ground state and the molecule or polaron state will be produced out of the Fermi sea. By using the Chevy-like ansatz, we investigate the properties of the molecule and attractive polaron states firstly and a transition between these two states will be found. Then, some properties of the repulsive polaron state will be introduced, such as the effective mass and the decay rate. Furthermore, the effect of an additional Fermi sea will be considered in this system. Finally, we will discuss the impurity problem in a two-dimensional system.