We present a combined experimental and theoretical study of beam formation from a cryogenic buffer gas cell. Atoms and molecules are loaded into the cell by laser ablation of a target, and are cooled and swept out of the cell by a flow of cold helium. We study the thermalization and flow dynamics inside the cell and measure how the speed, temperature, divergence and extraction efficiency of the beam are influenced by the helium flow. We use a finite element model to simulate the flow dynamics and use the predictions of this model to interpret our experimental results.

We demonstrate the deceleration of heavy polar molecules in low-field-seeking states by combining a cryogenic source and a traveling-wave Stark decelerator. The cryogenic source provides a high-intensity beam with low speed and temperature, and the traveling-wave decelerator provides large deceleration forces and high phase-space acceptance. We prove these techniques using YbF molecules and find the experimental data to be in excellent agreement with numerical simulations. These methods extend the scope of Stark deceleration to a very wide range of molecules.

The fluorescence spectrum resulting from laser excitation of the A(2)Π(1/2)←X(2)Σ(+) (0,0) band of ytterbium monofluoride, YbF, has been recorded and analyzed to determine the Franck-Condon factors. The measured values are compared with those predicted from Rydberg-Klein-Rees (RKR) potential energy curves. From the fluorescence decay curve the radiative lifetime of the A(2)Π(1/2) state is measured to be 28 ± 2 ns, and the corresponding transition dipole moment is 4.39 ± 0.16 D. The implications for laser cooling YbF are discussed.

It has been proposed that a Rydberg electron interacting via the zero-range Fermi pseudopotential with a nearby perturbing atom could bind into ultralong range Rydberg molecular states1. An experiment with ultracold Rydberg atoms in a dense rubidium magneto-optical trap (MOT) recently realized the existence of the istotropic utralong range Rydberg molecules2. We predict the existence of a class of ultralong range macroscopic Rydberg molecules which can be created in ultracold traps from a polar molecule and a Rydberg atom3. The molecular binding is due to the long range anisotropic interaction of the Rydberg electron with the permanent dipole of the trapped polar molecule. These giant molecules have deep binding energies, Eb ≃ 20 GHz, are ultralong range, R ≃ 2000 a0, and are well protected from the non-adiabatic avoided crossings, which could lead to their premature demise. A double-well structure, shown in Fig. 1(left), arrises in which the orientation of the polar molecule dipole, d, is controlled by the Rydberg electron, as shown schematically in Fig. 1(right). The lowest vibrational levels in L (0L) and R (0R) wells in Fig. 1 (left) can be coherently coupled via a microwave Raman transition. The on-resonance, but weak intensity two-photon transition, via an intermediate vibrational state (vR) in the extended right well efficiently transfers population between different electronic states. The configurations in the L and R wells, respectively, are with the molecular dipole pointing toward or away from the ionic core. The coherent Raman scheme ensures that the molecular dipole orientations become entangled. The dipolar interaction of two polarized giant Rydberg molecules could be coupled to the internal superposition states of the polar molecules.