Charge-dipole-dipole interactions in cold gases

Charge-dipole interactions are very common interactions among atoms and molecules, especially materials that can emit light or contain free charges. The second-order charge-dipole interactions, proportional to 1 R 4 , are stronger than the second-order dipole-dipole interactions or van der Waals interactions, proportional to 1 R 6 , at longer distances. In reality, there is more than one atom or charge; therefore, we focus on few-body charge-dipole interactions, such as charge-dipole-dipole interactions. Laser cooling and trapping allow us to study such interactions with much higher precision. In this article, charge-dipole interactions will be investigated in cold gases. To increase the interaction strength, we excite the cold atoms to highly excited states, Rydberg states. Here, we treat one Rydberg atom as a dipole; the excited electron and the ion core are the two poles of an electric dipole. Specifically, we study charge-atom interactions in cold Rydberg gases. The laser-cooled lower level atoms were excited to highly excited states, and we scanned a microwave to look at the line shape of a particular transition between two Rydberg states. It has been shown that adding a charge can enhance atom-atom interactions under certain circumstances.