The recent advance in techniques for laser cooling and manipulation of neutral atomic gases has opened the possibility of unveiling the quantum behaviour of individual atoms at extremely low temperatures (few tens of microKelvin).
Optical manipulation also allows to prepare an atom in a highly excited electronic state: one of the valence electrons is excited by a laser pulse, leading to the formation of a so called "superatom” , or a largely “inflated “ atom, with radius stretched out thousands of times. In this way, effectively the electric dipole moment is largely increased and the system behaves like an “antenna”, capable of emitting and receiving electric signals.
For these reasons, ultra-cold Rydberg atoms offer a unique experimental tool to study and control interactions amongst atomic systems since they appear to be "frozen", moving negligibly during the time scale of experimental interest. In a cloud of ultracold Rydberg atoms, the dynamics are determined by dipole-dipole interactions only. These interactions can be tuned, by controlling the electronic state (principal quantum number), external electric fields or even the interatomic distance.
The Cold Atoms Lab (www.physics.open.ac.uk/~sbergamini) has recently been awarded a grant (470,000 £) by EPSRC to carry out a research project aimed at studying cold atoms in Rydberg states.
Novel experiments will be performed to study the interactions of small clouds of atoms stored in micrometer-sized dipole traps, when a controllable number of atoms (one or more) in each cloud are excited to a Rydberg state. Exploiting the high sensitivity of Rydberg atoms to electric fields, the ultimate goal is to use a single excited atom in an optical trap to probe the electric field of another Rydberg atom or arrays of Rydberg atoms.
