Coulomb crystals in a cryogenic Paul trap for sympathetic cooling of molecular ions and highly charged ions

Abstract

Electron beam ion traps used for spectroscopy of highly charged ions (HCI) produce a deep trapping potential leading to high temperatures of the stored ions, and thus limiting the achievable spectral resolution. A novel device at the Max-Planck-Institut für Kernphysik, the Cryogenic linear Paul Trap Experiment (CryPTEx), attached to an electron beam ion trap, provides a new experimental platform to overcome these limitations. The trap assembly operates at a temperature of 4 K and offers optical access for quantum manipulation and imaging of the trapped ions. Since forbidden optical transitions in HCI do not support direct laser cooling, sympathetic cooling with Coulomb crystals of singly charged ions such as Be+ or Mg+ will be applied in order to reach the natural linewidth of optical forbidden transitions in HCI of interest. With the added advantage of long ion trapping times resulting from residual gas pressures of H2 at 4 K below 10−15 mbar, CryPTEx has been commissioned in collaboration with the Ion Trap Group in Århus using rovibrationally cooled MgH+ ions. Strong suppression of the black body radiation at the trap center, ion storage times of about 28 hours, and largely enhanced population of the rovibrational ground state were achieved

Rovibronic Spectroscopy of Sympathetically Cooled 40CaH+

“…Many approaches to controlling the rotational state have been proposed and implemented including cryogenic cooling of the molecule's surroundings [32], optical pumping [21,33,34], and buffer gas cooling [35][36][37]. AlH + can be rotationally cooled by optical pumping using pulse shaping to filter out the blue frequencies to drive only the P branch transitions.…”

“… 32). In Ca + , Figure2.3, the 4 2 P 1/2 has a lifetime of 7.1 ns with a 1:18 branching ratio to decay to the metastable 3…”

Spectroscopy of Molecular Ions in Coulomb Crystals

“…Many approaches to controlling the rotational state have been either proposed or implemented including cryogenic cooling of the molecule’s surroundings, optical pumping, , and buffer gas cooling . AlH + can be rotationally cooled by optical pumping on rovibronic transitions using pulse shaping to filter out the blue frequencies to drive only the P branch transitions .…”

Identification of the Predicted5s−4fLevel Crossing Optical Lines with Applications to Metrology and Searches for the Variation of Fundamental Constants

“…In most of the proposed HCIs with atomic number Z ¼ 55-98 and in charge states from 7 to 35, the complex electronic structures are experimentally unknown, and accurate calculations are extremely difficult. In view of novel techniques for sympathetically cooling HCIs in Paul traps [13][14][15] aiming at quantum logic spectroscopy on highly forbidden transitions [16], such data are urgently required.Observations from quasar absorption spectra have suggested a spatial variation of the value of the fine-structure constant α over cosmological dimensions [17], characterized by a dipolar distribution with a value of 10 −6 GLyr −1 . Laboratory experiments [18][19][20][21] have not yet reached the accuracy needed to test this dipolar pattern, which translates to a temporal variation of 10 −19 yr −1 [22] due to the motion of the Earth.…”

“…In most of the proposed HCIs with atomic number Z ¼ 55-98 and in charge states from 7 to 35, the complex electronic structures are experimentally unknown, and accurate calculations are extremely difficult. In view of novel techniques for sympathetically cooling HCIs in Paul traps [13][14][15] aiming at quantum logic spectroscopy on highly forbidden transitions [16], such data are urgently required.…”