Minimization of ion micromotion in a Paul trap

Abstract

Pulsed rotating supersonic source for merged molecular beams Rev. Sci. Instrum. 83, 064102 (2012) An atomic beam source for fast loading of a magneto-optical trap under high vacuum Rev. Sci. Instrum. 83, 055102 (2012) A low phase noise microwave source for atomic spin squeezing experiments in 87Rb Rev. Sci. Instrum. 83, 044701 (2012) Ultra-sensitive high-precision spectroscopy of a fast molecular ion beam Micromotion of ions in Paul traps has several adverse effects, including alterations of atomic transition line shapes, significant second-order Doppler shifts in high-accuracy studies, and limited confinement time in the absence of cooling. The ac electric field that causes the micromotion may also induce significant Stark shifts in atomic transitions. We describe three methods of detecting micromotion. The first relies on the change of the average ion position as the trap potentials are changed. The second monitors the amplitude of the sidebands of a narrow atomic transition, caused by the first-order Doppler shift due to the micromotion. The last technique detects the Doppler shift induced modulation of the fluorescence rate of a broad atomic transition. We discuss the detection sensitivity of each method to Doppler and Stark shifts, and show experimental results using the last technique. ͓S0021-8979͑98͒05610-2͔

High-precision spectroscopy of the HD+ molecule at the 1-p.p.b. level

“…In addition, excess micromotion may be caused by unwanted rf fields arising from geometrical imperfections of the trap electrode structure or phase differences between the rf electrodes [31]. In an ideal linear rf trap, micromotion is strictly radially oriented, but small imperfections in the trap geometry can cause excess micromotion with a component along the trap axis and laser direction, thus adding phase-modulation sidebands to each hyperfine component in the (0, 2)→(8, 3) spectrum.…”

“…As the laser propagates virtually parallel to the trap axis, and since the HD + ions are always located near the trap axis, we are primarily concerned with the possible axial micromotion component. The HD + axial micromotion amplitude x HD + can be determined through fluorescence measurements of a trapped string of beryllium ions using a modified version of the photon-rf field correlation technique [31]. The idea here is to radially displace a string of about 10 Be + ions by ~100 μm by applying a static offset field.…”

Molecules and Ions at Very Low Temperatures

“…Over the past decades, trapping in radiofrequency (RF) ion traps has been established as a standard technique to store and manipulate atomic and molecular ions in mass spectrometry, [17] charged-particle physics, [18] laser cooling, [19] and ion-trap based quantum-information processing. [15] The most common type of ion-storage devices used in conjunction with laser-cooling experiments are linear Paul traps [20] which typically consist of an assembly of four cylindrical electrodes arranged in a quadrupolar configuration as shown in Fig.…”

Ultrasensitive detection of force and displacement using trapped ions

“…We report the detection of forces with a sensitivity 390±150 yN/ √ Hz (more than three orders of magnitude better than existing reports using nanofabricated devices [7]), and discriminate ion displacements ∼18 nm. Our technique is based on the excitation of tunable normal motional modes in an ion trap [13] and detection via phase-coherent Doppler velocimetry [14,15], and should ultimately permit force detection with sensitivity better than 1 yN/ √ Hz [16]. Trappedion-based sensors could permit scientists to explore new regimes in materials science where augmented force, field, and displacement sensitivity may be traded against reduced spatial resolution.…”

“…It may also be desirable to exploit sub-Doppler cooling and sideband-detection mechanisms [17,18] Schematic of pulse sequencing/triggering for phase-coherent detection. This scheme is based on previous studies of micromotion nulling in a Paul trap [14] and studies of plasma oscillations in a Penning trap [15], with the important distinction that the excitation and detection are segregated into different parts of the measurement procedure. …”