Experiments with Ion Traps

The Ion-Trapping Group at the University of Granada is the first experimental group at the Department of Atomic, Molecular and Nuclear Physics. Daniel Rodríguez arrived to the University of Granada in 2009 and he joined a project with Antonio M. Lallena as PI. This year he got a Ramón y Cajal contract and in 2010, he got the first project from the Spanish Government as PI. The project started in January 2011, and by the end of that year he was awarded with a Starting Grant from the European Research Council. In the last years many students from different academic levels, most of them from the University of Granada, has joined the project.

The ion trap and laser laboratory is the only laboratory of this kind in Spain, resulting in the appointment of the facility as a Singular Laboratory at UGR. We started to build the laboratory in March 2012 in the framework of the project TRAPSENSOR funded by the European Research Council. We also got funding from the Spanish Ministry of Economy and Competitiveness, and the regional Government of Andalusia. Part of this money comes through the FEDER program and the University of Granada.


Figure 1: upper part: sketch representing a Penning trap with parallel plates and an ion oscillating in the axial direction. The current induced by the ion flows through an LC circuit, which is resonant with the oscillation frequency of the ion. Lower part: Sketch of the system proposed to use the fluorescence photons from a single laser-cooled 40Ca+ ion instead of an electronic circuit. The 40Ca+ ion is cooled to the Doppler limit (Click for bigger version).

The most remarkable aim envisaged in the laboratory is to build a system to couple two ions stored in different traps. The traps have a common electrode in order to make the electric charge induced by the ion flow between the traps. This idea was proposed in the nineties by D.J. Heinzen and D.J. Wineland but has not been realized so far. A successful completion of this system will allow substituting electronic detection, shown in the upper part of Fig. 1, by the detection of fluorescence photons (lower part in Fig. 2) and this will increase the sensitivity in mass spectrometry, which is important to perform measurements on superheavy elements produced in fusion-evaporation reactions at linear accelerators such at GSI-Darmstadt or to use the mass of specific nuclei for neutrino physics The left side of Fig. 2 shows a laser-cooled 40Ca+ ion in one of the ion traps built at the University of Granada. The right side of the figure shows the geometry of the open-ring trap built at the University for these kinds of experiments


Figure 2: Left: fluorescence photons from a laser 40Ca+ ion collected with an Electron Multiplier CCD camera. The ions are created inside the trap shown on the right side and they are laser-cooled. The fluorescence photons collected within a certain solid angle are collimated to be register in to the EMCCD for the studies (Click for bigger version).

The characterization of a single laser-cooled ion as an optical sensor has been realized in this trap and the corresponding results have been published in Scientific Reports (link to the manuscript), which belongs to the Nature Publishing Group. In addition, we have performed the characterization procedure with two laser-cooled ions in the same apparatus in order to extend this optical detection method for the case of ions stored in Penning traps. These last results have been published in a special issue of Journal of Modern Optics (link to the manuscript). Figure 3 shows the baseline of the optical detection method, where we studied the response of the axial distribution of the fluorescence images under dipolar excitations.


Figure 3: Left: Fluorescence images of one and two laser-cooled ions in the radiofrequency trap. The axial spacing between the ions is approximately 30 microns. Right: Axial distributions of the fluorescence images for the single ion case (blue curve) and for two-ion case (red curves). Click for bigger version.


  • Francisco Domínguez, Íñigo Arrazola, Jaime Doménech, Julen S. Pedernales, Lucas Lamata, Enrique Solano and Daniel Rodríguez. “A Single-Ion Reservoir as a High-Sensitive Sensor of Electric Signals”
    Scientific Reports 7, 8336 (2017).
  • F. Domínguez, M. J. Gutiérrez, I. Arrazola, J. Berrocal, J. M. Cornejo, J. J. Del Pozo, R. A. Rica, S. Schmidt, E. Solano and D. Rodríguez. “Motional studies of one and two laser-cooled trapped ions for electric-field sensing applications”
    Journal of Modern Optics 65, 613-621 (2018).