Long-Range Atom–Ion Rydberg Molecule: A Novel Molecular Binding Mechanism

Abstract

We present a novel binding mechanism where a neutral Rydberg atom and an atomic ion form a molecular bound state at a large internuclear distance. The binding mechanism is based on Stark shifts and level crossings that are induced in the Rydberg atom due to the electric field of the ion. At particular internuclear distances between the Rydberg atom and the ion, potential wells occur that can hold atom–ion molecular bound states. Apart from the binding mechanism, we describe important properties of the long-range atom–ion Rydberg molecule, such as its lifetime and decay paths, its vibrational and rotational structure, and its large dipole moment. Furthermore, we discuss methods of how to produce and detect it. The unusual properties of the long-range atom–ion Rydberg molecule give rise to interesting prospects for studies of wave packet dynamics in engineered potential energy landscapes.

Nonadiabatic decay of metastable states on coupled linear potentials

“…Potential wells emerging from two intersecting diabatic potentials with opposite slopes, coupled by an (approximately) constant interaction, are abound in physics and chemistry [1,2]. Examples include atom traps in optical lattices with Raman couplings [3][4][5][6], confinement of Bose-Einstein condensates on RF-dressed magnetic potentials with spin-dependent slopes [7][8][9][10], atom interferometry in RF-dressed magnetic guiding potentials [11][12][13][14], dressed atom-RF-field states in cavity-QED systems [15,16], Rydberg atoms in external fields [17][18][19], intersecting potential energy curves with radially dependent adiabatic electronic states in Rydberg-Rydberg [20,21], Rydberg-ground [20,22] and Rydberg-ion [23][24][25][26] molecules, and a host of conical intersections in quantum chemistry [27][28][29][30]. If the slopes of the diabatic potentials have opposite signs, the upper adiabatic potential surface exhibits a potential well, and the classical motion in this well is a bound, periodic oscillation about the avoided crossing.…”

“…If the slopes of the diabatic potentials have opposite signs, the upper adiabatic potential surface exhibits a potential well, and the classical motion in this well is a bound, periodic oscillation about the avoided crossing. Such cases are common in molecular physics, as in Rydberg-ion molecules [23][24][25][26], and in atom trapping [31][32][33]. The semi-classical Landau-Zener (LZ) tunneling equation [34,35] has sometimes been applied to estimate nonadiabatic decay rates of quantum states in such adiabatic-potential wells.…”

Spatial imaging of a novel type of molecular ions

“…With the advent of experimental techniques enabling the control of cold ions immersed in ultracold neutral atoms [22][23][24][25][26][27][28][29], the study of weakly-bound neutral molecules can be extended to molecular ions. In this context, a new type of Rydberg molecule has been theoretically proposed, consisting of an ion and a Rydberg atom [30,31]. The novel binding mechanism is based on a flipping dipole of the Rydberg atom interacting with the electric field around the ion.…”

“…2a. The methods for calculating the potential are covered in the Methods section and are motivated by recent publications [30,31]. The deep outer potential V 1 hosts a series of vibrational states (Fig.…”

Probing ultracold gases using photoionization fine structure

“…The full potential of this method will unfold in future work with the inclusion of spin-orbit coupling effects and multiple scattering off of several perturber atoms. Future extensions of our theory will permit to investigate the emerging diverse settings of Rydberg interacting systems, such as Rydberg-Rydberg [34][35][36][37] and, very recently, Rydberg-ion, bound states [38][39][40], using the fine structure of photoionization and its variants as a sensitive probe.…”