Many-body quantum dynamics and induced correlations of Bose polarons

Abstract

We study the ground state properties and non-equilibrium dynamics of two spinor bosonic impurities immersed in a one-dimensional bosonic gas upon applying an interspecies interaction quench. For the ground state of two non-interacting impurities we reveal signatures of attractive induced interactions in both cases of attractive or repulsive interspecies interactions, while a weak impurityimpurity repulsion forces the impurities to stay apart. Turning to the quench dynamics we inspect the time-evolution of the contrast unveiling the existence, dynamical deformation and the orthogonality catastrophe of Bose polarons. We find that for an increasing postquench repulsion the impurities reside in a superposition of two distinct two-body configurations while at strong repulsions their corresponding two-body correlation patterns show a spatially delocalized behavior evincing the involvement of higher excited states. For attractive interspecies couplings, the impurities exhibit a tendency to localize at the origin and remarkably for strong attractions they experience a mutual attraction on the two-body level that is imprinted as a density hump on the bosonic bath.

Pump-probe spectroscopy of Bose polarons: Dynamical formation and coherence

“…1(f) and 1(g)] is negligible, suggesting that attractive induced interactions cannot be directly unveiled by the observed shift. A result that complements earlier predictions indicating that attractive induced interactions are suppressed in the repulsive regime [60,98]. Indeed, for g BI > 0 the density of the BEC is less distorted compared to g BI < 0 [60,61].…”

“…A result that complements earlier predictions indicating that attractive induced interactions are suppressed in the repulsive regime [60,98]. Indeed, for g BI > 0 the density of the BEC is less distorted compared to g BI < 0 [60,61]. Accordingly, the impurities are less attracted to these distortions and consequently to each other.…”

“…is the σspecies (σ = B, ↑, ↓) one-body reduced density matrix, | (t ) is the MB wave function, and ρ (1) σ (x; t ) is the one-body density, see also Appendix D. Importantly, |g (1) σ (x, x ; t )| ∈ [0, 1] indicates the spatially resolved deviation of a MB wave function from a corresponding product state. Specifically, if |g (1) σ (x, x ; t )| = 1, then the system is termed fully coherent;, otherwise, coherence losses occur, signifying the buildup of correlations [60,99]. Indeed, the instantaneous |g (1) ↑ (x, x ; t d = 2ω)| for g BI = 1.5 h 3 ω/m clearly dictates that the quasiparticle remains adequately coherent since, e.g., |g (1) ↑ (x = −5 √h /mω, x = 5 √h /mω;…”

“…Additionally, interactions among quasiparticles in liquid helium mixtures [67,68] and cuprates [69,70] are considered to be responsible for conventional and high-T c superconductivity [71][72][73][74][75][76][77]. Here we consider a Bose-Einstein condensate (BEC) with one or two impurities of either bosonic or fermionic nature immersed into it and track the emergent Bose polaron formation [42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61] with a PPS radiofrequency protocol analogous to the one used in the experiment of Ref. [78].…”

“…In systems where the interaction strength between the impurity and the background is not larger than the interaction strength within the background gas, polaronic excitations can have long lifetimes. However, beyond that limit substantial losses of coherence occur with a temporal orthogonality catastrophe (TOC) [59][60][61]83] being imprinted in the probe spectrum. The TOC emerges due to the relaxation of the quasiparticles into energetically lower-lying, phaseseparated states.…”