Creating a gas of ultracold ion pairs out of long-range Rydberg molecules

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The goal of this proposal is the exploration of a new approach to create a strongly-coupled neutral plasma. Strongly-coupled neutral plasmas consist of an equal number of positive and negative charges, whose interaction strength is much stronger than the thermal energy of the system. These plasmas exhibit strong spatial correlations between the charged particles. The many-body physics of such systems plays an important role in the core of gas-planets or fusion devices.The central idea of this project is the transformation of an ultracold gas of cesium atoms into a cesium-ion and –anion plasma. In a first step, pairs of ground-state atoms will be transformed into a longrange Rydberg molecule by absorption of a photon (photoassociation). The binding of such a molecule results from the scattering of the almost-free Rydberg electron off a ground-state atom within its orbit. The molecular states will be chosen such that their binding is dominated by scattering in a channel with a single quantum of angular momentum (p-wave scattering). In this case, dipole-allowed transitions exist between the scattering state of the electron-neutral system and the bound ground state of the cesium-anion.In a next step, the long-range Rydberg molecule will be transformed into an ion-pair state by stimulated emission, driven from a laser pulse in the mid infra-red. The ion-pair state is a bound state of an ion and an anion, whose properties are dominated by the Coulumb interaction between the charged particles. Because the Hamiltonian of system corresponds to the one of a Rydberg atom, the binding energies of the vibrational states of the ion-pair will also be described by Rydberg’s formula. Because the reduced mass of the ion-anion system is much larger than the one of an electron-ion system, these molecules are called “heavy-Rudberg molecules”. In a last step, the dissociation of heavy-Rydberg molecules into a free ion-anion pair will be investigated. The combination of all three steps will thus convert a gas of ultracold atoms into a gas of ultracold ions and anions.