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We report the observation of spin-singlet ultralong-range Rydberg butterfly molecules consisting of a ground-state atom bound to a Rydberg atom by $P$-wave scattering of ${}^{87}\mathrm{Rb}$Rydberg electrons from ${}^{87}\mathrm{Rb}\left(5\mathrm{s}\right)$atoms. A three-photon excitation scheme enables the photoassociation of these molecules by weakly admixing $\mathrm{Rb}\left(18f_{7/2}\right)$states. The measured binding energies, kilo-Debye permanent electric dipole moments, and lifetimes are in excellent agreement with theory. Two long-lived vibrational levels, red detuned from the $\mathrm{Rb}\left(18f_{7/2}\right)$threshold, are observed. This experiment is a foundational step in the production of ultracold anions and heavy Rydberg ion-pair systems. 

Resonant energy transfer (RET) between the equal parity 1s65s ${}^3{\mathrm{S}}_1$and 1s66s ${}^3{\mathrm{S}}_1$Rydberg levels in helium has been observed in low-temperature ( $\sim 80\mathrm{mK}$) collisions with ammonia molecules that undergo inversion transitions in their X ${}^1{\mathrm{A}}_1$ground electronic state. This hybrid Rydberg-atom–polar-molecule resonant energy transfer represents a monopole-dipole energy exchange reaction that necessarily requires spatial overlap of the Rydberg-electron and molecular wave functions. Calculations that account explicitly for the charge-dipole interaction between the Rydberg electron and the molecule provide a quantitative explanation of the observations. Total parity is conserved in the reaction through the mixing of collisional angular momentum in the atom-molecule complex. This work opens opportunities to expand the toolbox for quantum science with charge-dipole-mediated energy exchange in hybrid atom–polar-molecule platforms. 

Abstract We propose leveraging strong and ultrastrong light-matter coupling to efficiently generate and exchange nonclassical light and quantum matter states. Two initial conditions are considered: (a) a displaced quadrature-squeezed matter state, and (b) a coherent state in a cavity. In both scenarios, polaritons mediate the dynamical generation and transfer of nonclassical states between light and matter. By monitoring the dynamics of both subsystems, we uncover the emergence of cavity-induced beatings in the collective matter oscillations. The beating period depends on the particle density through the vacuum Rabi splitting and peaks sharply under light-matter resonance conditions. For initial condition (a), nonclassicality is efficiently transferred from matter to photons under strong and ultrastrong coupling. However, for initial condition (b), nonclassical photonic states are generated only in the ultrastrong coupling regime due to the counter-rotating terms, highlighting the advantages of ultrastrong coupling. Furthermore, in the ultrastrong coupling regime, distinctive asymmetries relative to cavity detuning emerge in dynamical observables of both light and matter. The nonclassical photons can be extracted through a semi-transparent cavity mirror, while nonclassical matter states can be detected via time-resolved spectroscopy. This work highlights that polariton states may serve as a tool for dynamically generating and transferring nonclassical states, with potential applications in quantum technology.