Many-Body Physics with Trapped Ions
When ions are laser cooled to temperatures in the mK range, they freeze out in crystalline structures, so called Coulomb crystals. In these crystals the ionized atoms can be resolved individually and observed by laser fluorescence, see photos below. Depending on the trapping parameters the crystals take on different phases in one to three dimensional structures. When a symmetry breaking phase transition is crossed adiabatically, i.e. faster than the speed of sound in the crystal, topological defects can occur [Pyka et al., Nat. Commun. 4, 2291 (2013)]. This happens when the ions cannot communicate the new symmetry they take on and different domains are formed inside the crystal with incompatible orientation. These defects have the physical properties of discrete solitons and show a highly nonlinear behavior [Partner et al., New J. Phys. 15, 103013 (2013), Landa et al., Phys. Rev. Lett. 104, 043004 (2010)]. By analogies the behavior of our crystals can be transferred to various other systems in Nature, from solid-state to cosmological systems. We use the well-controlled environment of our crystals to investigate the nature of symmetry breaking phase transitions and transport phenomena in nano-scale atomic structures.
See also: Cosmology in the lab using laser-cooled ions
High-Precision Spectroscopy in In+/Yb+ ion crystals
Today's best optical clocks based on laser cooled ions reach fractional frequency inaccuracies of less than 10-17 [Huntemann et al., Phys. Rev. Lett. 116, 063001 (2016), Chou et al., Phys. Rev. Lett. 116, 063001 (2010)]. At that level of accuracy clocks can serve as quantum sensors to measure gravitational potentials with a height resolution in the cm range above the geoid, as well as to test fundamental theories like the predictions of Einstein's general relativity. While neutral lattice clocks based on 104 laser cooled atoms profit from a high signal-to-noise-ratio and thus a low quantum projection noise, optical ion clocks profit from the highly accurate control of the single trapped ion. In our project we are investigating a new type of optical ion clock based on multiple laser-cooled ions which are trapped in chains and arrays and thus allow to significantly improve the stability of clocks. With such clocks relative frequency resolutions of 10-18 can be reached in 1/100th of the time than today's best ion clocks. We are investigating chains of 115In+ ions that are sympathetically cooled with 172Yb+ ions. These ions are trapped in segmented and integrated, scalable trap structures, that allow for a high level of control of the ion dynamics and make ion crystals accessible for time and frequency metrology.
|Simplified level scheme of the 172-Yb ion.||Simplified level scheme of the 115-In ion.|
Indium ions show excellent properties for an optical atomic clock [Herschbach et al., Appl. Phys. B 107, 891 (2012)] and can directely be detected via the intercombination line to the 3P1 state. Yb+ ions on the other hand are used as a versatile tool to sympathetically cool larger crystals of In+ ions, but as well have interesting properties by themselves for fundamental tests of our standard model [Dzuba et al., Nature Phys. (2016), doi:10.1038/nphys3610].
Departments 4.4, 5.3 and 5.5, PTB
B. Chichkov group at Laser Zentrum Hannover
W. H. Zurek at Los Alamos National Lab, USA
K. Hayasaka, National Institute of Information and Communication Technologies, Japan
B. Reznik group, Tel Aviv University, Israel
M. Plenio group, Universität Ulm, Germany
R. Nigmatullin, University of Oxford, UK
S. Bagayev group, Institute for Laser Physics, Novosibirsk, Russia
This research is undertaken within the European Metrology Research Programme (EMRP) project SIB04 IonClock.
We acknowledge funding by DFG under grant number ME 3648/1-1, the DAAD, PTB and the cluster of excellence QUEST.