Ground-state properties of ultracold trapped bosons with an immersed ionic impurity

Abstract

We consider a trapped atomic ensemble of interacting bosons in the presence of a single trapped ion in a quasi-one-dimensional geometry. Our study is carried out by means of the newly developed multilayer-multiconfiguration time-dependent Hartree method for bosons, a numerical exact approach to simulate quantum many-body dynamics. In particular, we are interested in the scenario by which the ion is so strongly trapped that its motion can be effectively neglected. This enables us to focus on the atomic ensemble only. With the development of a model potential for the atom-ion interaction, we are able to numerically obtain the exact many-body ground state of the atomic ensemble in the presence of an ion. We analyze the influence of the atom number and the atom-atom interaction on the ground state properties. Interestingly, for weakly interacting atoms, we find that the ion impedes the transition from the ideal gas behavior to the Thomas-Fermi limit. Furthermore, we show that this effect can be exploited to infer the presence of the ion both in the momentum distribution of the atomic cloud and by observing the interference fringes occurring during an expansion of the quantum gas. In the strong interacting regime, the ion modifies the fragmentation process in dependence of the atom number parity which allows a clear identification of the latter in expansion experiments. Hence, we propose in both regimes experimentally viable strategies to assess the impact of the ion on the many-body state of the atomic gas. This study serves as the first building block for systematically investigating the many-body physics of such hybrid system.

Cold hybrid ion-atom systems

“…In recent years, a significant effort has been undertaken to simulate in a numerically efficient way the many-body Schrödinger equation describing an ion in a one-dimensional atomic cloud. The ground-state properties of ultracold bosons in interaction with a static (i.e., tightly trapped) ion impurity have been investigated by (Schurer et al, 2014) by means of the multiconfigurational time-dependent Hartree method for bosons (Alon et al, 2008;Cao et al, 2013;Krönke et al, 2013). A harmonically trapped ensemble of atoms with a static ion has been considered, with the effective 1D Hamiltonian…”

Capture dynamics of ultracold atoms in the presence of an impurity ion

“…The interaction between the ion at z I and an atom at z A behaves in 1D at large distances as e z z (2( ) ) 2 A I 4 α − − up to a minimal cutoff distance R 1D [32], where α is the polarizability of the atoms and e the elementary charge. For numerical many-body simulations with MCTDHB it is more convenient, however, to define a model potential as [28]:…”

Confinement-induced resonances in ultracold atom-ion systems

“…Their combination defines indeed a new quantum system characterised by an interaction with different energy and length scales with respect to ultracold atoms, which allows to study the formation of molecular ions [13,14], polarons [15], density bubbles [16], mesoscopic entanglement [17,18], novel ground state properties [19] and collective excitations [20], and quantum information processing [21][22][23]. Further, the interaction of the atoms with the phonons of an ion crystal may serve to investigate solid-state phenomena [24].…”