The work performed in the project included:
(1) The development of a cryogenically cooled (30 K) experimental apparatus for preparing cold, electrostatically trapped Rydberg atoms and molecules. This apparatus was used for laser spectroscopic studies of long-lived Rydberg states of nitric oxide (NO). It was also used in experiments to guide, accelerate, decelerate and trap molecules in these long-lived Rydberg states. Systematic studies of the decay processes of the trapped molecules were performed. The results of this work provided new insights in the role of rotational and vibrational channel interactions, and vibrational excitation on the slow decay of these Rydberg states in NO.
(2) The implementation of a new 2D spectroscopy technique, in which laser photoexcitation to Rydberg states was combined with detection by pulsed electric field ionisation in a slowly-rising electric field, to allow direct identification of Rydberg series in small molecules to which individual excited states belong. This method was used, e.g. to identify and characterise long-lived Rydberg states of NO prior to deceleration and electrostatic trapping.
(3) First experiments to observe quantum-state-resolved resonant energy transfer in collisions of Rydberg atoms with polar molecules, and the first demonstration of control over this energy transfer processes using electric fields. This work was initially performed with Rydberg helium atoms in pulsed supersonic beams and room temperature (300 K) gases of ammonia. It was then extended to temperatures below 100 mK in an intra beam collision apparatus to allow the first observation of effects of van der Waals interactions on the process of resonant energy in this type of collision system.
(4) Experimental and theoretical studies of quantum mechanical tunnelling processes that lead to ionisation of Rydberg atoms and molecules in strong electric fields. This work represented a new way to study tunnel ionisation in atoms and molecules and allowed the refinement of Rydberg-state-selective electric field ionisation methods used to detect excited species throughout the project.
(5) The realisation of new experimental tools for controlling the motion of atoms and molecules in Rydberg states using time-varying inhomogeneous electric fields. The approaches developed in this work allowed atoms and molecules in a wider range of excited states to be confined and guided, than was previously possible. These tools have applications, e.g. in studies of collisions and decay processes involving Rydberg atoms and molecules, including resonant energy transfer.
(6) The development, and first demonstration, of a method to perform matter-wave interferometry with atoms in Rydberg states by exploiting the quantum-state-dependent forces that can be exerted on them using inhomogeneous electric fields. This new and original experimental technique has applications in the study of weak long-range interactions of Rydberg atoms with polar molecules, studies of quantum mechanical geometric phases for particles with large electric dipole moments, and measurements of acceleration due to gravity for antimatter.
(7) The first demonstration of a cavity-enhanced Ramsey spectroscopy technique to probe and manipulate Rydberg atoms located above chip-based superconducting microwave resonators. The methodology and experimental techniques used in this work open new opportunities for high-sensitivity non-destructive detection of Rydberg atoms or molecules, and studies of long-range interactions between Rydberg atoms/molecules and surfaces.
