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arXiv:2608.12716 · Physical Review A

Predissociation dynamics of charged long-range Rydberg molecules

Neethu Abraham, Panagiotis Giannakeas, Matthew T. Eiles

Published Oct 23, 2026• 0 citations
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Abstract

We investigate predissociation in homonuclear ($^{87}$Rb$^*$$^{87}$Rb$^+$) and heteronuclear ($^{87}$Rb$^*$$^{7}$Li$^+$) long-range Rydberg atom-ion molecules. Owing to their micron-scale bond lengths, these dissociate on time scales far removed from those of more tightly bound diatomic molecules. We employ the eigenchannel $R$-matrix method to compute predissociation rates for a broad range of principal quantum numbers $n$. The rates depend strongly on the mass, but more remarkably display a rapid and periodic variation as a function of $n$ as well as within a single vibrational ladder. A semiclassical Landau-Zener-Stückelberg analysis reveals that Stückelberg interference governs the decay process and produces the observed variation in the molecular lifetime. Although the heavy mass of the homonuclear Rb molecule constrains its predissociation rates to a sub-kHz level, the lighter molecule $^{87}$Rb$^*$$^{7}$Li$^+$ dissociates on time scales competitive with radiative and collisional decay. This can enable in situ study of non-adiabatic decay via ion microscopy.

DOI
10.1103/n299-png4

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We investigate predissociation in homonuclear (87^{87}87Rb^*$$^{87}Rb+^++) and heteronuclear (87^{87}87Rb^*$$^{7}Li+^++) long-range Rydberg atom-ion molecules. Owing to their micron-scale bond lengths, these dissociate on time scales far removed from those of more tightly bound diatomic molecules. We employ the eigenchannel RRR-matrix method to compute predissociation rates for a broad range of principal quantum numbers nnn. The rates depend strongly on the mass, but more remarkably display a rapid and periodic variation as a function of nnn as well as within a single vibrational ladder. A semiclassical Landau-Zener-Stückelberg analysis reveals that Stückelberg interference governs the decay process and produces the observed variation in the molecular lifetime. Although the heavy mass of the homonuclear Rb molecule constrains its predissociation rates to a sub-kHz level, the lighter molecule 87^{87}87Rb^*$$^{7}Li+^++ dissociates on time scales competitive with radiative and collisional decay. This can enable in situ study of non-adiabatic decay via ion microscopy.
We examine an effectively one-electron system with three positive nuclei composed of a Rb * 87 Rydberg atom interacting with a pair of Rb + 87 ions and predict the existence of metastable vibrationally bound states of Rb 3 2 + 87 . These molecules are long-range trimers whose stability rests on the presence of core-shell electrons and favorable scaling of the Rydberg atom's quadrupole moment with the principal quantum number n . Unlike recently observed ion-Rydberg dimers, whose binding is due to internal flipping of the Rydberg atom's dipole moment, the binding of Rb 3 2 + 87 arises from the interaction of the ions with the Rydberg atom's quadrupole moment. The stability of these trimers is highly sensitive to n . For n ≤ 35 , we estimate that the lifetime of the bound states should be limited by intercore tunneling of the Rydberg electron, which creates an instability in the system. However, we predict that the rate of this process decreases significantly with n , such that already for n = 38 it is comparable in magnitude to the rate of spontaneous emission of the Rydberg state. The decreasing depth of the binding potential at larger n will further lead to an increase in the tunneling rate of the vibrational states from the molecular binding potential to dissociative regions of the adiabatic potential energy surface. Nonetheless, at n = 38 , this mechanism is only relevant for the highest-excited vibrational states in the binding potential. Published by the American Physical Society 2024
Heavy-Rydberg ion-pair states, molecular quantum systems that are bound by their long-range pure Coulomb attraction, are formed through Rydberg atom collisions with molecules that attach low energy electrons. Collisions of potassium Rydberg atoms K(np) with the attaching species CCl4 and SF6 lead, respectively, to dissociative and non-dissociative electron attachment with subsequent formation of bound ion-pair states K+..Cl- and K+..SF6-.\nThe experimental apparatus used to produce and detect heavy-Rydberg ion-pair states consists of a reaction region and a separate analysis region. It separates a fraction of the product ion pairs from the parent Rydberg atoms, eliminating spurious background signals associated with blackbody-induced and electric-field ionization of Rydberg atoms. A position sensitive detector in the analysis region is employed to measure their velocity, angular, and binding energy distribution and lifetimes. Measurements of the spatial distribution of ion pairs provide information on their velocity and angular distributions, and their binding energy distribution is measured using electric field-induced dissociation. The lifetime of the ion-pair states is influenced by multiple processes including internal-to-translational energy transfer, autodetachment of the electron, and neutralization through charge transfer.\nThe experimental results are compared with the results of a Monte Carlo collision code that models both the initial Rydberg electron attachment and the subsequent evolution and molecular dynamics of the ion pairs. This model highlights the factors such as the kinematics of the Rydberg atom and the attaching particle and energy released in dissociation (in the case of dissociative attachment) that are important in governing ion pair formation. The model calculations are in good agreement with the experimental data.
Ultra-long-range Rydberg molecules (ULRMs) have attracted significant interest due to their unique electronic properties and potential applications in quantum technologies. We theoretically investigate the formation and characteristics of heteronuclear ULRMs, focusing on Rb-Cs systems. We explore the vibrational energy levels of heteronuclear nD ULRMs and compare them with homonuclear counterparts. We also predict the formation of polyatomic heteronuclear ULRMs, discussing how the binding energy and spectral features evolve as the number of ground-state atoms increases. Our theoretical predictions are presented in terms of molecular spectra and provide insight into the formation dynamics of these systems. The study further explores the potential applications of heteronuclear ULRMs in quantum information processing, quantum simulation, and precision measurements, offering new avenues for future research in many-body physics and quantum technologies.
The lifetimes and decay channels of ultralong-range Rydberg molecules created in a dense Bose-Einstein condensate are examined by monitoring the time evolution of the Rydberg population using field ionization. Studies of molecules with values of the principal quantum number, nnn, in the range n=49n=49n=49 to n=72n=72n=72 that contain tens to hundreds of ground-state atoms within the Rydberg electron orbit show that their presence leads to marked changes in the field ionization characteristics. The Rydberg molecules have lifetimes of $\ensuremath{\sim}1\ensuremath{-}5\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{s}$, their destruction being attributed to two main processes: formation of Sr2+{\mathrm{Sr}}_{2}{}^{+}Sr2​+ ions through associative ionization and dissociation induced through LLL-changing collisions. The observed loss rates are consistent with a reaction model that emphasizes the interaction between the Rydberg core ion and its nearest-neighbor ground-state atom. The measured lifetimes place strict limits on the time scales over which studies involving Rydberg species in cold, dense atomic gases can be undertaken and limit the coherence times for such measurements.
The decay of Rydberg-atom--ion molecules (RAIMs) due to nonadiabatic couplings between electronic potential-energy surfaces is investigated. We employ the Born-Huang representation and perform numerical simulations using a Crank-Nicolson algorithm. The nonadiabatic lifetimes of rubidium RAIMs for the lowest ten vibrational states, $\ensuremath{\nu}$, are computed for selected Rydberg principal quantum numbers, nnn. The nonadiabatic lifetimes are found to generally exceed the radiative Rydberg-atom lifetimes. We observe and explain a trend of the lifetimes as a function of $\ensuremath{\nu}$ and nnn, and attribute irregularities to quantum interference arising from a shallow potential well in an inner potential surface. Our results will be useful for future spectroscopic studies of RAIMs.
We present a kinetic model based on coupled rate-equation simulations that accounts for state-detailed rate processes in the evolution of a molecular Rydberg gas to plasma. Calculations support a steady-state picture of Rydberg predissociation and its contribution to plasma dissipation. Inelastic collisions of electrons with Rydberg states efficiently transfer energy from and to the thermal bath of free electrons, giving rise to quasi equilibria of relatively high temperature. Dissipative effects that remove low- n population change the time course of this heating. Including statistically sampled channels of Rydberg predissociation with n - and ℓ-dependent lifetimes slows the relaxation to quasi equilibrium and retards the initial electron temperature increase. At later times, the dissociative loss of low- n population displaces this quasi equilibrium leading to continuous electron heating. Dissociation products appear at a rate that is controlled initially by the rate of Rydberg relaxation to quasi equilibrium. Thereafter, the overall rate at which the total dissociation consumes neutral molecules determines the decay rate for all levels. Simulations predict a total predissociation rate that is smaller than the initial rate of direct electron–ion dissociative recombination. At later times, residual predissociation displays an apparent first-order decay with a rate constant that fits well with experimental observations.