Correlated Quantum Dynamics of a Single Atom Collisionally Coupled to an Ultracold Finite Bosonic Ensemble

TL;DR

This paper investigates the complex quantum energy exchange between a single atom and a finite bosonic environment, revealing how correlations influence incoherent transfer processes and subsystem excitations.

Contribution

It provides a detailed ab-initio analysis of correlated quantum dynamics in a single atom coupled to a finite bosonic ensemble, highlighting the role of system-environment correlations.

Findings

Energy transfer accelerates with more bosons but becomes less complete.

Correlations are significant except during highly imbalanced energy distributions.

Energy transfer involves non-coherent states and specific excitations in the environment.

Abstract

We explore the correlated quantum dynamics of a single atom, regarded as an open system, with a spatio-temporally localized coupling to a finite bosonic environment. The single atom, initially prepared in a coherent state of low energy, oscillates in a one-dimensional harmonic trap and thereby periodically penetrates an interacting ensemble of $N_A$ bosons, held in a displaced trap. We show that the inter-species energy transfer accelerates with increasing $N_A$ and becomes less complete at the same time. System-environment correlations prove to be significant except for times when the excess energy distribution among the subsystems is highly imbalanced. These correlations result in incoherent energy transfer processes, which accelerate the early energy donation of the single atom and stochastically favour certain energy transfer channels depending on the instantaneous direction of transfer. Concerning the subsystem states, the energy transfer is mediated by non-coherent states of the single atom and manifests itself in singlet and doublet excitations in the finite bosonic environment. These comprehensive insights into the non-equilibrium quantum dynamics of an open system are gained by ab-initio simulations of the total system with the recently developed Multi-Layer Multi-Configuration Time-Dependent Hartree Method for Bosons.