2017/12/31 by Arturo Camacho-Guardian, A. Camacho-Guardian, Georg M. Bruun · 84 citations
Physics and Astronomy · #Bose–Einstein condensate #Cold Atom Physics and Bose-Einstein Condensates #Condensed matter physics #Physics #Quantum electrodynamics #Quantum mechanics #Quantum, superfluid, helium dynamics #Quasiparticle #Strong Light-Matter Interactions #Superconductivity #cond-mat.quant-gas
paper · pdf · doi:10.1103/physrevx.8.031042
published in Physical Review X 8(3) (American Physical Society) · 12 pages
openalex publication_date 2018/08/15 · arxiv created 2018/08/16 · arxiv updated 2018/08/17 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Landau's description of the excitations in a macroscopic system in terms of quasiparticles stands out as one of the highlights in quantum physics. It provides an accurate description of otherwise prohibitively complex many-body systems and has led to the development of several key technologies. In this paper, we investigate theoretically the Landau effective interaction between quasiparticles, so-called Bose polarons, formed by impurity particles immersed in a Bose-Einstein condensate (BEC). In the limit of weak interactions between the impurities and the BEC, we derive rigorous results for the effective interaction. They show that it can be strong even for a weak impurity-boson interaction, if the transferred momentumenergy between the quasiparticles is resonant with a sound mode in the BEC. We then develop a diagrammatic scheme to calculate the effective interaction for arbitrary coupling strengths, which recovers the correct weak-coupling results. Using this scheme, we show that the Landau effective interaction, in general, is significantly stronger than that between quasiparticles in a Fermi gas, mainly because a BEC is more compressible than a Fermi gas. The interaction is particularly large near the unitarity limit of the impurity-boson scattering or when the quasiparticle momentum is close to the threshold for momentum relaxation in the BEC. Finally, we show how the Landau effective interaction leads to a sizable shift of the quasiparticle energy with an increasing impurity concentration, which should be detectable with presentday experimental techniques.