A detailed theoretical investigation of the fundamental three-body antiproton-positronium system is presented, utilizing both quantum convergent close coupling and classical trajectory methods. We evaluate scattering cross sections for all major processes, including charge transfer and breakup, over a wide range of positronium kinetic energies and states with principal quantum number ${n}_{\mathrm{Ps}}\ensuremath{\le}6$. The study has significantly extended previous work, and the direct quantum-classical comparison has revealed a systematic approach to obtaining cross sections for arbitrarily high ${n}_{\mathrm{Ps}}$ . This is of major significance for prospective applications of collisions of excited positronium atoms in cold (anti-)atomic physics.A detailed theoretical investigation of the fundamental three-body antiproton-positronium system is presented, utilizing both quantum convergent close coupling and classical trajectory methods. We evaluate scattering cross sections for all major processes, including charge transfer and breakup, over a wide range of positronium kinetic energies and states with principal quantum number ${n}_{\mathrm{Ps}}\ensuremath{\le}6$. The study has significantly extended previous work, and the direct quantum-classical comparison has revealed a systematic approach to obtaining cross sections for arbitrarily high ${n}_{\mathrm{Ps}}$. This is of major significance for prospective applications of collisions of excited positronium atoms in cold (anti-)atomic physics.

Physical Review ADec 6, 20219 citations

Observation of Bose-Einstein condensation in a gas of chromium atoms

Axel Griesmaier, J. Stühler, Tilman Pfau

We have observed Bose-Einstein condensation of chromium atoms [1], whose large magnetic dipole moment is unique among all species that have been Bose-condensed so far. The arising magnetic forces are of anisotropic and long-range character and therefore introduce a novel type of interaction in the physics of ultracold quantum gases. In addition, it is expected that the character of the interaction present in a chromium BEC can be varied from mainly contact to purely dipolar utilizing one of the recently observed Feshbach resonances in 52Cr-collisions.We have observed Bose-Einstein condensation of chromium atoms [1], whose large magnetic dipole moment is unique among all species that have been Bose-condensed so far. The arising magnetic forces are of anisotropic and long-range character and therefore introduce a novel type of interaction in the physics of ultracold quantum gases. In addition, it is expected that the character of the interaction present in a chromium BEC can be varied from mainly contact to purely dipolar utilizing one of the recently observed Feshbach resonances in 52Cr-collisions.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIEApr 7, 20060 citations

Effect of Atomic Collisions

D. V. Skobelʹt︠s︡yn

Nonlinear OpticsJan 1, 19700 citations

Two-body and three-body dynamics in atom-ion experiments

Arne Härter

During the last few decades, the two fields of ultracold neutral atoms and of single trapped ions have undergone an amazing development. The incorporation of these systems into a single experiment exploits the complementary physical properties of the subsystems and opens up novel lines of research. I present experimental results obtained in one of the first hybrid atom-ion setups accessing the cold regime. Single ions interact with ultracold samples of 87Rb atoms. The collision energies are set by heating mechanisms in the Paul trap and are on the order of mK·kB. Interactions are generally strong and long-ranged. We observe elastic atom-ion scattering in the semi-classical energy regime in which the cross section depends on the collision energy and favors scattering at small angles. We were able to obtain a general good understanding of atom-ion two-body collisions. We observed sympathetic cooling of the ion over four orders of magnitude in energy through collisions with the ultracold atoms. Further, we utilized atom-ion scattering events to develop a novel method to compensate excess ion micromotion, the primary source of ion heating. Three-body collisions between two atoms and the ion play an important role. We identified these processes through the large amounts of energy that they release. This makes them detectable despite their suppression with respect to two-body collisions. We also showed that atom-ion three-body collisions become more prominent as the collision energy decreases. Finally, we employed our atom-ion apparatus to gain novel insights into three-body recombination between ultracold atoms. In these experiments the ion trap acts as an extremely sensitive ion detector. Through three-body recombination a Rb2 molecule is formed and can undergo ionization by absorbing photons from a strong laser. By scanning the frequency of the ionization laser we obtained a molecular spectrum and identified a relatively broad distribution over final molecular states.During the last few decades, the two fields of ultracold neutral atoms and of single trapped ions have undergone an amazing development. The incorporation of these systems into a single experiment exploits the complementary physical properties of the subsystems and opens up novel lines of research. I present experimental results obtained in one of the first hybrid atom-ion setups accessing the cold regime. Single ions interact with ultracold samples of 87Rb atoms. The collision energies are set by heating mechanisms in the Paul trap and are on the order of mK·kB. Interactions are generally strong and long-ranged. We observe elastic atom-ion scattering in the semi-classical energy regime in which the cross section depends on the collision energy and favors scattering at small angles. We were able to obtain a general good understanding of atom-ion two-body collisions. We observed sympathetic cooling of the ion over four orders of magnitude in energy through collisions with the ultracold atoms. Further, we utilized atom-ion scattering events to develop a novel method to compensate excess ion micromotion, the primary source of ion heating. Three-body collisions between two atoms and the ion play an important role. We identified these processes through the large amounts of energy that they release. This makes them detectable despite their suppression with respect to two-body collisions. We also showed that atom-ion three-body collisions become more prominent as the collision energy decreases. Finally, we employed our atom-ion apparatus to gain novel insights into three-body recombination between ultracold atoms. In these experiments the ion trap acts as an extremely sensitive ion detector. Through three-body recombination a Rb2 molecule is formed and can undergo ionization by absorbing photons from a strong laser. By scanning the frequency of the ionization laser we obtained a molecular spectrum and identified a relatively broad distribution over final molecular states.

Jan 1, 20130 citations

{n}_{\mathrm{Ps}}

. This is of major significance for prospective applications of collisions of excited positronium atoms in cold (anti-)atomic physics.