#	Pagina
attuale pagina	/open-h2020/projects/200804/results.html

Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - CAtMolChip (Cold Atmospheric Molecules on a Chip)

Teaser

Summary

The overall objectives of this project are to experimentally study collisions and decay processes of atoms and molecules in highly excited quantum states known as Rydberg states. The atoms and molecules of interest are those of importance in the chemistry and physics of the Earth\'s upper atmosphere. This work is carried out in a controlled laboratory environment. It exploits, and involves the development of, state-of-the art experimental techniques to confine and isolate the species of interest so that they can be studied on comparatively long timescales (on the order of milliseconds). This work is important in attaining a complete understanding of the detailed physical and chemical processes taking place in the environment in which live. The experimental methods developed through the project are also likely to be of benefit in other areas of research in fundamental physical chemistry and physics, including, e.g., studies involving antimatter, and for other applications.

Work performed

The work performed up to now in the context of the project includes:

(1) The development of a low-temperature (30 K) experimental apparatus for preparing cold trapped atoms and molecules in highly excited Rydberg states. This apparatus has so far been used to prepare and perform laser spectroscopic studies of long-lived Rydberg states of nitric oxide (NO) - with lifetimes on the order of 100 microseconds. It has also been used in experiments to guide, accelerate and decelerate beams of these long-lived Rydberg molecules while confined in the travelling electric traps of a chip-based Rydberg-Stark decelerator. Samples of NO Rydberg molecules decelerated from 700 m/s to zero mean velocity in the laboratory frame of reference have been electrostatically trapped in this apparatus for times in excess of 500 microseconds. Work is currently underway to perform systematic studies of the decay rates and decay pathways of these long-lived highly excited molecules.

(2) The first experiments to observe quantum-state-resolved resonant energy transfer in collisions of atoms in highly excited Rydberg states with polar ground state molecules, and the demonstration, for the first time, of control over these energy transfer processes using weak electric fields. This work was initially performed with helium atoms prepared in high Rydberg states in pulsed supersonic beams, and ammonia molecules in room temperature (300 K) effusive beams. We have now extended these studies down to collision energies corresponding to temperatures of 1 K. In this most recent work resonant energy transfer to individual Rydberg-Stark states from the inversion sublevels in ammonia has been resolved for the first time, and control over the transfer of rotational energy from the molecules to the atoms using electric fields has been observed.

(3) Experimental and theoretical studies of quantum mechanical tunneling processes that lead to ionisation of Rydberg atoms and molecules in strong electric fields have been performed. This work represents a new way to study tunnel ionisation in atoms and molecules and has allowed the refinement of Rydberg-state-selective electric field ionisation methods used in our experiments to detect Rydberg atoms and molecules.

(4) 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 allow atoms and molecules in a wider range of excited states to be confined and guided, than previously possible. They have applications in studies of collisions and decay processes of long-lived Rydberg states of small molecules, studies of resonant energy transfer in atom-molecule collisions at low temperature, and in other areas of chemistry and physics including studies involving antimatter.

(5) The development, and first demonstration of a method to perform matter-wave interferometry with atoms or molecules in high Rydberg states by exploiting their interactions with inhomogeneous electric fields. This new and original experimental technique has many potential applications including in the study of weak long-range interactions of Rydberg atoms or molecules with ground-state atoms or molecules.

Final results

The outcomes of each of the five work areas listed above have moved this research program well beyond the existing state of the art.

The low-temperature experimental apparatus developed incorporates a state-of-the-art decelerator and trap structure which had only previously been operated at room temperature. Its operation at a temperature of 30 K in this apparatus is a significant technical step forward that opens a wide range of new research opportunities that we are now taking advantage of.

The quantum-state-resolved and electric-field controlled resonant energy transfer processes studied in collisions of Rydberg atoms with polar ground state molecules had not previously been observed in such detail and with such high sensitivity. The particular energy transfer reactions studied may be considered ideal model systems with which to attain a thorough understanding of these processes.

The studies of ionisation dynamics and quantum mechanical tunnel ionisation rates that we have carried out as part of the project exceed the precision with which these processes have been investigated previously, and highlight the limitations theoretical methods used to calculate the rates, and timescales on which these processes occur.

The new experimental tools that we have developed to control the motion of highly excited atoms and molecules using time-varying inhomogeneous electric fields did not previously exist and allow the motion of samples in a wider range of quantum states to be controlled than was previously possible.

Finally, the approach to Rydberg-atom interferometry, using sequences of microwave and inhomogeneous electric field pulses that we have developed are ground breaking. They open a new era of coherent Rydberg atom/molecule optics, and many exciting possibilities for studies of atom-molecule and molecule-molecule interactions at low temperatures. As the project continues we expect to build on the results and methods that we have developed up to now, with a particular emphasis on studies of collisions and slow decay process of Rydberg states of NO, N2 and O2 in electrostatic traps.