Quantitative assessment and suppression of anharmonic potential of quadrupole linear radiofrequency ion traps with round electrodes

Abstract

Precision manipulation of the quantum coherence of radiofrequency (RF) ion trap systems is one of the most important prerequisites for the development of high-performance ion frequency standards, high-fidelity ion trap quantum computing, and ion precision spectroscopy. The anharmonic potential of the ion trap exacerbates the non-ideal kinetic properties of the trapped ions and the simple harmonic motions of the heated ions, which in turn constrain the coherence time of the trapped ion systems. In this study, we developed a precision assessment and optimization method for the potential field of a quadrupole linear RF ion trap with round electrodes based on the joint weight suppression of the multi-order anharmonic potential, which is applicable for ion ensembles of cloud, liquid, and crystalline forms, and for different ion numbers. By quantifying the potential of each radial order of the decoupled transient RF potential, we established the quantitative loss relationship between the structure parameter of the linear RF ion trap with round electrodes and the trapping potential and outlined the influence of the structure parameter of the trap on the weight of the anharmonic potential. We determined the optimal structure parameter k (the ratio of pole radius re to radius r0 of the maximum trapping field) of the quadrupole linear ion trap with round electrodes as 1.1451447, which minimizes the overall anharmonic potential and achieves the highest reported accuracy (Reuben et al., 1996) [1]. This result provides a basis for the solution of problems in physics such as obtaining long-time trapping under low heating rate, precision manipulation of coherence, motion effect suppression, and efficient cooling of 3D ion systems, which are conducive to quantum coherence with time delays, spectral measurement approaching the theoretical accuracy limit, and high-performance frequency standards of 3D ion systems.