Speeding up adiabatic ion transport in macroscopic multi-Penning-trap stacks for high-precision experiments

Abstract

Multi-Penning traps are an excellent tool for high-precision tests of fundamental physics in a variety of applications, ranging from atomic mass measurements to symmetry tests. In such experiments, single ions are transferred between distinct trap regions as part of the experimental sequence, resulting in measurement dead time and heating of the ion motions. Here, we report a procedure to reduce the duration of adiabatic single-ion transport in macroscopic multi-Penning-trap stacks by using ion-transport waveforms and electronic filter predistortion. For this purpose, transport adiabaticity of a single laser-cooled ⁹Be⁺is analyzed via Doppler-broadened sideband spectra obtained by stimulated Raman spectroscopy, yielding an average heating per transport of 2.6 ± 4.0 quanta for transport times between 7 and 15 ms. Applying these techniques to current multi-Penning trap experiments could reduce ion transport times by up to three orders of magnitude. Furthermore, these results are a key requisite for implementing quantum logic spectroscopy in Penning trap experiments.

Keywords: Experimental nuclear physics; Quantum metrology; Raman spectroscopy.

Fig. 1. Experimental setup, energy levels and experimental sequence.

a Cross-section view of the Be and coupling traps. Electrodes are cylinder-shaped and made of gold-plated oxygen-free high thermal conductivity copper. They have an inner diameter of 9 mm for the Be trap and 8 mm for the coupling trap. The single laser-cooled ⁹Be⁺ion is transported back and forth over a distance of 22.3 mm from electrode 3 (E3) in the Be trap to electrode 9 (E9) in the coupling trap. Each electrode is equipped with a 3-stage low-pass RC filter to minimize electrical noise. The trap electrodes are color-coded for identification. b Relevant internal level scheme of ⁹Be⁺in a 5 Tesla magnetic field. The cooling and detection (D) as well as the repumper transition (R) are represented by light and dark blue arrows, respectively. The Raman transitions are depicted by dark and light green arrows for Raman transitions 1 (R1) and 2 (R2), respectively. Energy levels are not to scale. c Simplified schematic of the trap voltage electronics. The electrode voltages, generated by an arbitrary waveform generator (AWG), are amplified and applied to the electrodes at cryogenic temperatures using filters at different temperature stages (room temperature, 60 K and 5 K). R₁, R₂ and R₃ are 5.0 kΩ, 5.2 kΩ and 7.1 kΩ, respectively. C₁, C₂ and C₃ are 4.8 nF. d Measurement cycle scheme, where t_cool and t_tp are the cooling and transport times, respectively.

Fig. 2. Voltage waveforms.

a Voltage waveforms with (solid lines) and without (dashed lines) filter predistortion as a function of time to transport a ⁹Be⁺ion back and forth between the Be and coupling traps within 2t_tp = 14 ms at an axial trap frequency of 435 kHz. b Voltage difference between voltage waveforms with and without filter predistortion for the same transport time and trap frequency. Different colors denote different electrodes according to the color code shown in Fig. 1a.

Fig. 3. Heating per transport.

a Heating per transport for several transport times t_tp using voltage waveforms without filter predistortion. Each data point (red, representing the mean) and the respective error (blue,  ± standard deviation) are obtained from the Gaussian envelope of a sideband spectrum acquired after ion transport. A total of around 20 sidebands per spectrum were probed, where each sideband scan is obtained from 1250 Raman interrogations. The black dashed line shows the transport-induced heating averaged for 10 ms ≤t_tp≤15 ms transport times. Gray dashed lines filled in light gray show the error bands of the averages with a confidence level of  ± one standard deviation. The solid black line shows an exponential decay fit to the data to guide the eye. b Heating per transport for several transport times t_tp using voltage waveforms with filter predistortion. The black dashed line shows the transport-induced heating averaged for all transport times.

Fig. 4. Resolved sideband spectra.

a Resolved sideband spectrum after transport for a transport time of t_tp = 7 ms without filter predistortion. b Resolved sideband spectrum after transport for a transport time of t_tp = 15 ms using filter predistortion. Each data point (blue, representing the mean) and the respective error (clear blue,  ± standard deviation of the mean) are obtained from 50 Raman interrogations after transport. Red lines are Lorentzian fits to the sideband data, clear blue dashed lines are Gaussian envelope fits to the sideband maxima. ν_Ref = 138.909014 GHz is a reference frequency close to ν₀.