Lattice Bose polarons at strong coupling and quantum criticality

Year: 2025

Authors: Alhyder R., Colussi V.E., Cufar M., Brand J., Recati A., Bruun G.M.

Autors Affiliation: Inst Sci & Technol Austria ISTA, Campus 1, A-3400 Klosterneuburg, Austria; Aarhus Univ, Ctr Complex Quantum Syst, Dept Phys & Astron, Ny Munkegade 120, DK-8000 Aarhus C, Denmark; Univ Trento, Pitaevskii BEC Ctr, CNR INO, I-38123 Trento, Italy; Univ Trento, Dipartimento Fis, I-38123 Trento, Italy; Infleqtion Inc, 3030 Sterling Circle, Boulder, CO 80301 USA; Te Whai Ao Dodd Walls Ctr Photon & Quantum Technol, Auckland 0632, New Zealand; Massey Univ, New Zealand Inst Adv Study, Ctr Theoret Chem & Phys, Private Bag 102904, Auckland 0745, New Zealand.

Abstract: The problem of mobile impurities in quantum baths is of fundamental importance in many-body physics. There has recently been significant progress regarding our understanding of this due to cold atom experiments, but so far it has mainly been concerned with cases where the bath has no or only weak interactions, or the impurity interacts weakly with the bath. Here, we address this gap by developing a new theoretical framework for exploring a mobile impurity interacting strongly with a highly correlated bath of bosons in the quantum critical regime of a Mott insulator (MI) to superfluid (SF) quantum phase transition. Our framework is based on a powerful quantum Gutzwiller (QGW) description of the bosonic bath combined with diagrammatic field theory for the impurity-bath interactions. By resumming a selected class of diagrams to infinite order, a rich picture emerges where the impurity is dressed by the fundamental modes of the bath, which change character from gapped particle-hole excitations in the MI to Higgs and gapless Goldstone modes in the SF. This gives rise to the existence of several quasiparticle (polaron) branches with properties reflecting the strongly correlated environment. In particular, one polaron branch exhibits a sharp cusp in its energy, while a new ground-state polaron emerges at the O(2) quantum phase transition point for integer filling, which reflects the nonanalytic behavior at the transition and the appearance of the Goldstone mode in the SF phase. Smooth versions of these features are inherited in the polaron spectrum away from integer filling due to the influence of Mott physics on the bosonic bath. We furthermore compare our diagrammatic results with quantum Monte Carlo calculations, obtaining excellent agreement. This accuracy is quite remarkable for such a highly non-trivial case of strong interactions between the impurity and bosons in a maximally correlated quantum critical regime, and it establishes the utility of our framework. Finally, our results show how impurities can be used as quantum sensors and highlight fundamental differences between experiments performed at a fixed particle number or a fixed chemical potential.

Journal/Review: SCIPOST PHYSICS

Volume: 19 (1)      Pages from: 2-1  to: 2-39

More Information: This work has been supported by the Danish National Research Foundation through the Center of Excellence CCQ (Grant agreement No. DNRF156) , the Independent Research Fund Denmark-Natural Sciences via Grant No. DFF-8021-00233B. This research was supported in part by the National Science Foundation under Grant No. NSF PHY-1748958. This project has received financial support from Provincia Autonoma di Trento and the Italian MIUR through the PRIN2017 project CEnTraL (Protocol No. 20172H2SC4) . The work was supported by the Marsden Fund of New Zealand (Contract No. MAU 2007) , from government funding managed by the Royal Society of New Zealand Te Aparangi. We acknowledge support by the New Zealand eScience Infrastructure (NeSI) high-performance computing facilities in the form of a merit project allocation. This research used resources of the Oak Ridge Leadership Computing Facility at the Oak Ridge National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC05-00OR22725.
KeyWords: Gas; Superfluid; Insulator; Atoms
DOI: 10.21468/SciPostPhys.19.1.002