Lasersystem
Final Report Abstract
After more than 60 years of successfully trapping ions in Paul traps and more than 30 years of confining atoms in optical dipole traps we aimed to do the first steps to combine these fields. We achieved the trapping of a single ion in an optical dipole potential in the year 2010, followed by an ion in a 1D-optical lattice in the year 2012. However, the trapping performance (lifetime and coherence times) of the ions in the close detuned optical trap (at 280nm for 24Mg+) was limited by off-resonant scattering and the related recoil heating from the dipole laser. This trapping regime precluded the proposed applications, such as permitting experimental quantum simulation and studies of ultra-cold interaction. In addition, it does not permit the identification of other heating effects arising from the interplay of the charge with e.g. electric field and laser intensity fluctuations, that are different from the dominant recoil heating, the latter well studied for neutrals. The main components of the laser system we have been applying for were required to provide far detuned optical dipole traps for both, ions and neutral atoms. Combined, they have been proposed to provide a bi-chromatic dipole trap for Rb and Ba+ at 1064nm and 532 nm. The 1064nm wavelength is red detuned for both species, while the 532nm remain red for Ba+ (relevant transition at 493 nm) and blue for Rb (relevant transition at 780 nm). Adjusting the relative power of the spatially overlapped beams was proposed to allow to tune the depth of the optically traps individually. It has enabled the following projects within the first three years: Optical trapping of 138Ba+ ions in the absence of radio-frequency fields via a fardetuned dipole trap at 532nm, suppressing photon scattering by three orders of magnitude and the related recoil heating by four orders of magnitude. To enhance the prospects for optical as well as hybrid traps, we demonstrated a method for stray electric field compensation to a level below 9mVm^-1, exploiting the spatial dependent Stark shift of the dipole laser. This result was key for the successful application for an ERC consolidator grant. We further 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 compared to our previous work, and measured an upper bound of the total heating rate. The achieved isolation from the environment opens a path to a novel regime of ultracold interactions of ions and atoms at previously inaccessible collision energies, and may permit 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. In addition, we realized Coulomb crystals within the optical dipole trap and performed spectrometry on the collective vibrational (phonon) degree of freedom.
Publications
- Long lifetimes in optical ion traps
A. Lambrecht, J. Schmidt, P. Weckesser, M. Debatin, L. Karpa, T. Schaetz
- „A far-off-resonance optical trap for a Ba+ ion” Nature Communications. Nat. Commun. 7, 11839 (2016)
T. Huber, A. Lambrecht, J. Schmidt, L. Karpa, T. Schaetz
(See online at https://doi.org/10.1038/ncomms6587) - „Trapping Ions and Atoms Optically“. Journal of Physics B 50, (2017)
T. Schaetz
(See online at https://doi.org/10.1088/1361-6455/aa69b2)
