Rf Ion Trap Research Articles

Kinetic Energy of Trapped Ions Cooled by Buffer Gas

The average kinetic energy of 40Ca+ ions is measured by the method of evaporating ions in an rf ion trap. The kinetic energy of the ion 40Ca+ varies from 0.5 eV to 0.2eV with changing buffer gas pressure from 10−7 mbar to 10−5 mbar. The Brownian motion model is also introduced to calculate the average kinetic energy of the trapped ions.

Storage of protonated water clusters in a biplanar multipole rf trap

We present the storage properties of protonated water clusters H+(H2O)n (n=1-4) in an improved biplanar ion trap. The design is based on our recently reported realization of a biplanar multipole radiofrequency (rf) ion trap (Debatin et al 2008 Phys. Rev. A 77 033422). The new experimental setup is composed of the ion trap in tandem time-of-flight configuration for mass-selective ion loading and mass-selective detection of stored ions. Special attention is paid to the supersonic discharge cluster source and our improved realization of a biplanar multipole ion trap with a simplified electrode layout. The source performance is presented and mass-selective loading into our trap is demonstrated with H+(H2O)n clusters. We achieve stable trapping of H+(H2O)n clusters (n=1–4) with storage lifetimes of 3–12 s, which is comparable to former achievements with stable atomic Ar+ ions in the first trap generation. Collision-induced cluster dissociation during the loading process is observed.

Infrared spectra and structures of diamantyl and triamantyl carbocations

Gas-phase infrared spectra have been recorded for the diamantyl and triamantyl carbocations by infrared multiple photon dissociation (IRMPD) spectroscopy using the free electron laser FELIX. Chemical ionization of the neutral parent diamondoid molecule in an rf ion trap is accompanied by H-atom loss, forming a stable closed-shell carbocation. Comparing the IRMPD spectra with harmonic DFT calculations permits to determine the structures of the species trapped in our set-up. Comparison of experimental and calculated spectra suggests that H-atom abstraction occurs on a tertiary carbon (CH group) rather than on a secondary carbon (CH 2 group), as also indicated by the calculated relative energies of the various isomers. Combining experimental results and DFT calculations, we compare the spectra of neutral and carbocationic forms of adamantane, diamantane and triamantane. Substantial differences are observed between the IR spectra of neutral and ionic species. In the ions, the 3 μ m CH stretching modes become much weaker, while the other mid-IR modes strongly gain in intensity. An intense band centered at 1200 cm −1 due to a CH/CH 2 bending mode appears to be characteristic of the dehydrogenated cationic species. Finally, the intensities of the low frequency modes ( ≤ 900 cm −1) associated with carbon cage deformations appear to be most sensitive to the ionization and dehydrogenation state of the molecules.

Observation of ion Coulomb crystals in a cryogenic linear octupole rf ion trap

Ion Coulomb crystals of laser-cooled ${\text{Ca}}^{+}$ ions have been observed in a cryogenic linear octupole rf ion trap for the first time. Due to the almost field-free central region, large ion crystals containing over ${10}^{4}$ ions of millimeter size were successfully produced. The shapes of the crystals can be manipulated by changing the static voltages applied to the octupole rods and the endcap electrodes. Quasi-two-dimensional Coulomb crystals consisting of a small number of ions were also observed with single-ion sensitivity. When a large number of ions is crystallized in the octupole trap, a new kind crystal image with a dip along the axial direction was obtained. The results show that a linear octupole trap and multipole traps are available for producing large, cold, and novel ion Coulomb crystals. The planar ring-type crystal which has not been observed before may lead to future interesting applications.

High-resolution spectroscopy ofH201g+hyperfine structure: A sensitive probe of nuclear structure and the hyperfine anomaly

Using 201Hg+ contained within a linear quadrupole rf ion trap that is part of an atomic clock, we report the first high-resolution spectroscopy on the hyperfine structure of 201Hg+. We measure the absolute ground state hyperfine interval to be 29.954365821130(171)(62)(10) GHz, more than 8 orders of magnitude improvement over the previous measurement. The first error estimate in parentheses is the statistical error in the shifted line center measurement, the second is systematic uncertainty, and the third is calibration uncertainty in the hydrogen maser reference standard. By comparison to the already accurately known ground state hyperfine interval for 199Hg+, we are able to derive a new value for the hyperfine anomaly in singly ionized mercury, Delta(S1/2, 199Hg+, 201Hg+) = -0.0016257(5), now limited by knowledge of the nuclear magnetic moment ratio.

Designing an ion trap for quantum simulation

Planar Coulomb crystals have been recently proposed for the implementation of quantumsimulation and computation. In order to put this idea into practice we designed aspecialized RF ion trap system....

Designing an ion trap for quantum simulation

Planar Coulomb crystals have been recently proposed for the implementation of quantum simulation and computation. In order to put this idea into practice we designed a specialized RF ion trap system. The design is based on extensive numerical simulations of planar Coulomb crystals in RF traps and the estimation of the error in quantum simulation and computation. Our trap would have reduced heating rates and large axial confinement frequencies would be available. Moreover, it provides very good optical access and it is easy to construct and operate.

Cryogenic ion trapping systems with surface-electrode traps

We present two simple cryogenic rf ion trap systems in which cryogenic temperatures and ultra high vacuum pressures can be reached in as little as 12 h. The ion traps are operated either in a liquid helium bath cryostat or in a low vibration closed cycle cryostat. The fast turn around time and availability of buffer gas cooling made the systems ideal for testing surface-electrode ion traps. The vibration amplitude of the closed cycled cryostat was found to be below 106 nm. We evaluated the systems by loading surface-electrode ion traps with (88)Sr(+) ions using laser ablation, which is compatible with the cryogenic environment. Using Doppler cooling we observed small ion crystals in which optically resolved ions have a trapped lifetime over 2500 min.

Evaporation of trapped anions studied with a 22-pole ion trap in tandem time-of-flight configuration

We have recently shown [J. Mikosch et al., Phys. Rev. Lett. 98, 223001 (2007)] that the storage time of a thermal ensemble of ions in a multipole radiofrequency (rf) ion trap is ultimately limited by ion evaporation. An analysis of the evaporation rate was used to determine an effective trap depth as a function of the rf amplitude. This revealed that already for moderate rf amplitudes and low average stability parameter $\ensuremath{\eta}$ the loss of ions is driven by nonadiabatic motion of the fastest ions in the rf field. Here we present the details of the experimental procedure together with our experimental apparatus, which combines a 22-pole rf ion trap with tandem time-of-flight mass spectrometry for ion selection and product analysis. We furthermore describe in detail the numerical and analytical models used in the interpretation of our results, which allows one to predict the most favorable trapping conditions in multipole rf ion traps. From a fit to our data we obtain a maximal value of the multipole stability parameter of ${\ensuremath{\eta}}_{\mathit{max}}=0.36\ifmmode\pm\else\textpm\fi{}0.02$ for adiabatic ion motion.

On the transport of atomic ions in linear and multidimensional ion trap arrays

Trapped atomic ions have become one of the most promising architectures for a quantum computer, and current effort is now devoted to the transport of trapped ions through complex segmented ion trap structures in order to scale up to much larger numbers of trapped ion qubits. This paper covers several important issues relevant to ion transport in any type of complex multidimensional rf (Paul) ion trap array. We develop a general theoretical framework for the application of time-dependent electric fields to shuttle laser-cooled ions along any desired trajectory, and describe a method for determining the effect of arbitrary shuttling schedules on the quantum state of trapped ion motion. In addition to the general case of linear shuttling over short distances, we introduce issues particular to the shuttling through multidimensional junctions, which are required for the arbitrary control of the positions of large arrays of trapped ions. This includes the transport of ions around a corner, through a cross or T junction, and the swapping of positions of multiple ions in a laser-cooled crystal. Where possible, we make connections to recent experimental results in a multidimensional T junction trap, where arbitrary 2-dimensional transport was realized.

On the transport of atomic ions in linear and multidimensional ion trap arrays

Trapped atomic ions have become one of the most promising architectures for a quantum computer, and current effort is now devoted to the transport of trapped ions through complex segmented ion trap structures in order to scale up to much larger numbers of trapped ion qubits. This paper covers several important issues relevant to ion transport in any type of complex multidimensional rf (Paul) ion trap array. We develop a general theoretical framework for the application of time-dependent electric fields to shuttle laser-cooled ions along any desired trajectory, and describe a method for determining the effect of arbitrary shuttling schedules on the quantum state of trapped ion motion. In addition to the general case of linear shuttling over short distances, we introduce issues particular to the shuttling through multidimensional junctions, which are required for the arbitrary control of the positions of large arrays of trapped ions. This includes the transport of ions around a corner, through a cross or T junction, and the swapping of positions of multiple ions in a laser-cooled crystal. Where possible, we make connections to recent experimental results in a multidimensional T junction trap, where arbitrary 2-dimensional transport was realized.

Evaporation of Buffer-Gas-Thermalized Anions out of a Multipole rf Ion Trap

We identify plain evaporation of ions as the fundamental loss mechanism out of a multipole ion trap. Using thermalized negative Cl- ions we find that the evaporative loss rate is proportional to a Boltzmann factor. This thermodynamic description allows us to extract the effective depth of the ion trap. As a function of the rf amplitude we find two distinct regimes related to the stability of motion of the trapped ions. For low amplitudes the entire trap allows for stable motion and the trap depth increases with the rf field. For larger rf amplitudes rapid energy transfer from the field to the ion motion can occur at large trap radii, which leads to a reduction of the effective trapping volume. In this regime the trap depth decreases again with increasing rf amplitude. We give an analytical parametrization of the trap depth for various multipole traps that allows predictions of the most favorable trapping conditions.

Controlled photoionization loading of 88Sr+ for precision ion-trap experiments

We report on a photoionization scheme for controlled loading of 88Sr+ ions into a radio-frequency (rf) ion trap. The two-step doubly-resonant process drives the 88Sr atom on the 5s21S0 – 5s5p1P1 transition at 461 nm using a frequency-doubled diode laser, and then excites the atom to the autoionizing (4d2+5p2) 1D2 state with 405 nm light from a free-running diode laser. This method of trap loading is quantitatively compared to electron bombardment loading, and shown to reduce the Sr vapour pressure required to load by four orders of magnitude. It also provides more than an order of magnitude reduction in the day-to-day variation of the voltages required to compensate micromotion. We additionally introduce a two-step atomic source consisting of an oven and hotplate, which reduces the number of impurities evaporated towards the trap. This is shown to significantly reduce fluctuations in required micromotion compensation voltages. The demonstrated reduction in flux and increased source purity are expected to improve the reliability of trap operation for precision ion-trap experiments.

Scaling and Suppression of Anomalous Heating in Ion Traps

We measure and characterize anomalous motional heating of an atomic ion confined in the lowest quantum levels of a novel rf ion trap that features moveable electrodes. The scaling of heating with electrode proximity is measured, and when the electrodes are cooled from 300 to 150 K, the heating rate is suppressed by an order of magnitude. This provides direct evidence that anomalous motional heating of trapped ions stems from microscopic noisy potentials on the electrodes that are thermally driven. These observations are relevant to decoherence in quantum information processing schemes based on trapped ions and perhaps other charge-based quantum systems.

Miniature Toroidal Radio Frequency Ion Trap Mass Analyzer

A miniature ion trap mass analyzer is reported. The described analyzer is a 1/5-scale version of a previously reported toroidal radio frequency (rf) ion trap mass analyzer. The toroidal ion trap operates with maximum rf trapping voltages about 1 kVp-p or less; however despite the reduced dimensions, it retains roughly the same ion trapping capacity as conventional 3D quadrupole ion traps. The curved geometry provides for a compact mass analyzer. Unit-mass resolved mass spectra for n-butylbenzene, xenon, and naphthalene are reported and preliminary sensitivity data are shown for naphthalene. The expected linear mass scale with rf amplitude scan is obtained when scanned using a conventional mass-selective instability scan mode combined with resonance ejection.

T-junction ion trap array for two-dimensional ion shuttling, storage, and manipulation

We demonstrate a two-dimensional 11-zone ion trap array, where individual laser-cooled atomic ions are stored, separated, shuttled, and swapped. The trap geometry consists of two linear rf-ion trap sections that are joined at a 90° angle to form a T-shaped structure. We shuttle a single ion around the corners of the T-junction and swap the positions of two crystallized ions using voltage sequences designed to accommodate the nontrivial electrical potential near the junction. Full two-dimensional control of multiple ions demonstrated in this system may be crucial for the realization of scalable ion trap quantum computation and the implementation of quantum networks.

Cold ion–neutral collisions in a hybrid trap

A dual hybrid ion–neutral trap has been built to study collisions between a cloud of ultracold atoms and small numbers of co-trapped atomic or molecular ions, in a common volume. Ultracold Na atoms are trapped in a vapour-cell magneto-optical trap (MOT), via a single-mode frequency-stabilized ring-dye laser, with repumping. A linear rf quadrupole Paul ion trap, centred on the MOT, co-traps selected atomic or molecular ions, for example Ca+. Control of the initial ion temperature involves laser cooling Ca+ ions via the resonant Fraunhofer K line at 397 nm. We showed the rf ion trap can operate simultaneously with the MOT without destroying the ultracold atom cloud. The goal is to investigate the physics of ion–neutral sympathetic cooling, the cooling by neutrals of translationally cold and vibrorotationally hot molecular ions (e.g. Na2 +(v*, J*)), and the observation of other ion–neutral processes near 0 K, of potential interest in astrophysics.

Rotating-radio-frequency ion traps

We discuss a radio-frequency (rf) ion trap, the rotating-radio-frequency (rotating-rf) trap, in which the motion of a charged particle is described by trigonometric functions rather than the usual Mathieu functions of a normal rf trap. In the rotating-rf trap, a rotating quadrupole electric field confines charged particles, whereas in a normal rf trap, an oscillating quadrupole electric field does. Ion motion in a rotating-rf trap is a superposition of two nondegenerate circular secular motions and two corresponding circular micromotions. The cases of applying a uniform dc magnetic field or a quadrupole dc electric field in addition to the rotating-rf field are also discussed. Confinement in a rotating-rf trap can be tighter than in a normal linear rf trap with the same experimental parameter values.

Size and composition dependence in CO oxidation reaction on small free gold, silver, and binary silver–gold cluster anions

Gas phase kinetics experiments with mass-selected gold, silver, and binary silver–gold cluster ions in a radio frequency (rf)-ion trap reactor are presented. For the catalytic CO combustion reaction, the adsorption of molecular oxygen onto the free clusters is identified as the first reaction step. A comparison of the measured O 2 adsorption reaction rate constants for the investigated Ag n Au m − ( n + m = 1, 2, 3) clusters reveals a pronounced size and composition dependence. Favorable activation of the oxygen molecular bond is only expected in the case of Au 2 −. In the reaction of the gold dimer with O 2 and CO, a coadsorption complex is identified at cryogenic temperatures as decisive reaction intermediate in the observed CO oxidation reaction. Through detailed reaction kinetics measurements in combination with first-principles calculations, a comprehensive understanding of the molecular details of the catalytic reaction cycle emerges. The obtained data also permit the determination of the CO 2 formation rate and the catalytic turn-over-frequency in the rf-ion trap reactor. In contrast to gold, odd size silver cluster anions are found to adsorb two oxygen molecules. These Ag n O 4 − complexes are proposed to be key intermediates in oxidation reactions with silver clusters involved, and first experimental indications for catalytic activity of selected cluster sizes are presented.

Simulations of the rf heating rates in a linear quadrupole ion trap

Molecular dynamics simulations of the ion clouds stored in a linear quadrupole rf ion trap are performed at low temperatures (0.1 mK--15 K). The introduction of periodic boundary conditions allowed us to study the translationally uniform ion cloud geometry. The time evolution of the kinetic energy of the ion cloud is monitored during the simulation and the increase in the kinetic energy of the cloud (rf heating) is determined; its dependence on temperature, trapping voltage, and the number of ions is studied. The dependence of rf heating rate on temperature shows that rf heating is undetectable until the temperature reaches approximately 0.5 K; it then increases rapidly until it reaches a maximum at around 2 K. It starts to decrease slowly at higher temperatures. The rf heating rate is shown to increase very sharply with the amplitude of the trapping voltage. The dependence of the rf heating rate on the number of ions shows the influence of the ion crystal shell structure at low temperatures, and has a simple linear dependence at higher temperatures.