Mass-selective removal of ions from Paul traps using parametric excitation

Abstract

We study a method for mass-selective removal of ions from a Paul trap by parametric excitation. This can be achieved by applying an oscillating electric quadrupole field at twice the secular frequency $$\omega _{\text {sec}}$$ ω sec using pairs of opposing electrodes. While excitation near the resonance with the secular frequency $$\omega _{\text {sec}}$$ ω sec only leads to a linear increase of the amplitude with excitation duration, parametric excitation near $$2\, \omega _{\text {sec}}$$ 2 ω sec results in an exponential increase of the amplitude. This enables efficient removal of ions from the trap with modest excitation voltages and narrow bandwidth, therefore, substantially reducing the disturbance of ions with other charge-to-mass ratios. We numerically study and compare the mass selectivity of the two methods. In addition, we experimentally show that the barium isotopes with 136 and 137 nucleons can be removed from small ion crystals and ejected out of the trap while keeping $$^{138}\text {Ba}^{+}$$ 138 Ba + ions Doppler cooled, corresponding to a mass selectivity of better than $$\Delta m / m = 1/138$$ Δ m / m = 1 / 138 . This method can be widely applied to ion trapping experiments without major modifications since it only requires modulating the potential of the ion trap.

Finite temperature spectrum at the symmetry-breaking linear-zigzag transition

“…On resonance, the amplitude of the driven mode increases linearly with F m [48]. In combination with a constant linear damping γ due to laser cooling of k 1 , a steady state with a constant, frequency-dependent mode amplitude Θ j (ω e ) can be reached after several oscillations.…”

Interactions of Ions and Ultracold Neutral Atom Ensembles in Composite Optical Dipole Traps: Developments and Perspectives

“…During experimental phases where the ion is confined by rf fields, this can be achieved by employing a method based on parametric excitation [45] of parasitic ions, e.g., Rb + and Rb + 2 , at twice their respective oscillation frequencies in the Paul trap [44,[46][47][48]. Owing to the exponential increase of the kinetic energy characteristic for parametric modulation, this excitation scheme in conjunction with a high mass resolution of at least 1/138 allows for the selective removal of different barium isotopes from an ion crystal [49] and is well suited for removing parasitic ions with a more distinct charge-to-mass ratio. With this technique, the trapping probability can be drastically improved, now allowing for efficient transfer into the bichromatic potential.…”

Micromotion minimisation by synchronous detection of parametrically excited motion

“…Without damping and if ω am = 2 ω 0 /n exactly, the system is unstable for any non-zero excitation amplitude h, and solutions are oscillatory with an exponentially growing amplitude over time. Parametric instabilities of this kind have been studied in a wide variety of systems [27], notably for mass-selective removal of ions from Paul traps [28]. Previous work on stray field compensation using parametric excitation [20][21][22] has also made use of the fact that these quickly-growing solutions can easily lead to large ion orbits where changes to the average fluorescence scattering rate of the ion during laser cooling can be observed.…”