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Trapping Ions in Atoms and Molecules Optically

Periodic Reporting for period 3 - TIAMO (Trapping Ions in Atoms and Molecules Optically)

Reporting period: 2018-08-01 to 2020-01-31

Isolating ions and atoms from the environment is essential in experiments on a quantum level. For decades, this has been achieved by trapping ions with radiofrequency (rf) fields and neutral particles with optical fields. Our group demonstrated the trapping of ions by interaction with light. We see these results and our proposal as starting point for finally combining the advantages of optical trapping and ions. In particular, ions provide individual addressability, high fidelities of operations and long-range Coulomb interaction, significantly larger compared to those of atoms and molecules.

The aim of this proposal is to (i) study and establish optically trapping of ions and atoms in general, to (ii) demonstrate the substantial improvement of our approach in the context of interaction and reaction at ultra-low temperatures and to (iii) explore further perspectives by adapting methodology of quantum optics to gain control and state-sensitive detection on the level of individual quanta within the merged ion-atom system.

The field of ultra cold chemistry is perfectly suited for this purpose, as a showcase as well as an area of research struggling with the fundamental quest for quantum effects. A simplifying summary of the quest might be:
How are interaction and chemical reactions proceeding at lowest temperatures? The classical concept predicts that approaching zero velocity is equivalent to standstill of any dynamics. On the one hand, deviations can be expected, since the classical model is ceasing to be appropriate when particle-wave dualism is gaining of importance. On the other hand, we might be inclined to see quantum mechanical properties as minor corrections - such as the uncertainty principle allowing for some residual but negligible interaction. However, in the regime of lowest temperatures quantum effects dominate, and chemistry is predicted to obey fundamentally different rules. Examples are:
(i) collisions of two species, necessary for a reaction, cannot be described as a billiard-like impact between hard spheres anymore, but rather as interfering waves, interacting at long range, which can coherently amplify or even completely annihilate each other.
(ii) energy barriers can mount above the kinetic energy, but can be efficiently passed by tunneling.
As a consequence and vision, quantum chemistry might permit to manipulate or even control reactions and their pathways by external fields, since the forces and related interactions become relevant compared to the kinetic energy.

Within this proposal, we aim at embedding optically trapped ions into quantum degenerate gases to reach temperatures, 4-5 orders of magnitude below the current state of the art. Our approach circumvents the currently inevitable excess kinetic energy in hybrid traps, where ions are kept but also driven by rf-fields. It permits to enter the temperature regime where quantum effects are predicted to dominate, (i) in many-body physics, including the potential formation and dynamics of mesoscopic clusters of atoms of a Bose-Einstein-Condensate, binding to the “impurity ion”, as well as (ii) the subsequent two-particle s-wave collisions, the ultimate limit in ultra-cold chemistry.
Further development of our novel and generic tools for “quantum engineering can be expected to propel several other striving fields of research, such as, experimental quantum simulations.
To address our short and long-term objectives, we select certain species (Ba+ and Rb,Li) and structure our work program into three interlinked work packages; (WP1) to realize the technological and experimental setup and work horse to provide the basic requirements of the project, to study and characterize the many-body physics (WP2) and quantum chemistry (WP3) in the ultra-cold regime.
We were capable to follow our schedule to directly address and reach the anticipated milestones. We did setup a bi-chromatic dipole trap for Rb and Ba+ by lasers at 1064nm and 532nm, immersed the ion into the atom ensemble and trapped both species all optically. The related manuscript is currently under review and published on the arXiv (arXiv 1609.06429v2 (2016)).
Long trapping times as well as low heating and decoherence rates, essentially isolating individual particles from the environment, are crucial ingredients for controlling these particles on the quantum level. In work performed during the project so far, we demonstrated that optical trapping and isolating ions can be performed on a level comparable to neutral atoms, boosting the lifetime by three orders of magnitude, and measure an upper bound of the total heating rate.
That is, we demonstrated optical trapping of an ion for several seconds in the absence of any rf field. The achieved isolation from the environment allows entering a new regime of ultracold interactions of ions and atoms at previously inaccessible collision energies and permits a novel class of experimental quantum simulations with ions and atoms in a variety
of versatile optical trapping geometries, e.g. bichromatic traps or higher-dimensional optical lattices.
The RF-micro-motion and the related fundamental heating of an atom–ion ensemble. Left: spatially ove
Examples of applications for optically trapped ions: (a) an ion immersed in an ultra-cold bath of at