From molecular spectroscopy to entanglement of atoms – a trek with supersonic velocity

The supersonic free-jet expansion technique is being used in different fields of research in physics, and physical chemistry to study vibrational and rotational molecular structures in ground and excited electronic energy states. The supersonic beam technique exploits a source of monokinetic, rotationally and vibrationally cold van der Waals (vdW) molecules that are very weakly bound in their ground electronic states. In this article we review experiments at the Jagiellonian University in Kraków (Poland) in which the supersonic free-jet beam serves as a source of ground-state vdW molecules in studies of neutral–neutral interactions between 12-group metal (Me = Zn, Cd, Hg) and 18-group noble gas (Ng = He, Ne, Ar, Kr, Xe) atoms. The experiments lead to determination of spectroscopical characteristics and interatomic potentials of MeNg and Me2 molecules, allowing determination of distinct trends in the Me–Ng and Me–Me interactions in different regions of internuclear separation. The determined interatomic potentials are also used in designing mechanisms of internal vibrational cooling of molecules photoassociated in magneto-optical traps. Recently, versatility of supersonic beams is confirmed in quantum information where the technique is planned to be used to create pairs of entangled atoms in experiments dedicated for testing of Bell’s inequality for atoms. A purpose of the experiment – which is in a preparational stage in our laboratory – is to create pairs of entangled cadmium atoms with regard to their nuclear spin orientations. It is planned to be achieved in supersonic molecular beams of cadmium dimers using two dye-laser pulses and stimulated Raman process leading to a controlled photodissociation of the molecule.