Planar Ion Trap Research Articles

High frequency properties of a planar ion trap fabricated on a chip.

We report on the measurement of the high frequency properties of a planar Penning ion trap fabricated on a chip. Two types of chips have been measured: the first manufactured by photolithographic metal deposition on a p-doped silicon substrate and the second made with printed circuit board technology on an alumina substrate. The input capacitances and the admittances between the different trap's electrodes play a critical role in the electronic detection of the trapped particles. The measured input capacitances of the photolithographic chip amount to 65-76 pF, while the values for the printed circuit board chips are in the range of 3-5 pF. The latter are small enough for detecting non-destructively a single trapped electron or ion with a specifically tuned LC resonator. We have also measured a mutual capacitance of ∼85 fF between two of the trap's electrodes in the printed circuit board chip. This enables the detection of single, or very few, trapped particles in a broader range of charge-to-mass ratios with a simple resistor on the chip. We provide analytic calculations of the capacitances and discuss their origin and possible further reduction.

Genetic algorithm parallel optimization of a new high mass resolution planar electrostatic ion trap mass analyzer.

The study and design of high-resolution mass analyzers is a very important task in mass spectrometry. A planar electrostatic ion trap (PEIT) mass analyzer with image charge detection and FT-based data processing has been developed, theoretically simulated, and experimentally validated. However, the 10 ring electrode configuration (PEIT-10) is difficult for mechanical construction and voltage tuning; moreover, few methods have been reported for optimizing the performance of multi-electrode mass analyzers. In this article, a simplified PEIT-7 mass analyzer was designed, and a genetic algorithm parallel optimization (GAPO) method was developed for optimizing multiple voltage settings of the new PEIT-7 mass analyzer to achieve spatial and energy isochronicity as well as iso-coordinate property. The automatic voltage optimization processes for the reduction of time aberration and spatial aberration showed that the developed GAPO method can significantly improve the optimization efficiency (the optimal voltage set being found within 5 hours with a maximum time aberration of 15 ps and a maximum z aberration of 0.10 μm). Based on the results obtained from the GAPO method, the resolving power of the PEIT-7 mass analyzer for six groups of ions with closely packed masses (m/z = 117.000 Th to 117.010 Th) was demonstrated, and a mass resolution of 171k was achieved at an acquisition time of 200 ms. The established GAPO method facilitates the design and optimization of high-resolution mass analyzers and may be useful for the design of other multi-electrode ion optical devices.

Measurement of ion displacement via RF power variation for excess micromotion compensation

We demonstrate a method of micromotion minimization of a trapped ion in a linear Paul trap based on the precision measurement of the ion trapping position displacement due to a stray electric field in the radial plane by ion fluorescence imaging. The amount of displacement in the radial plane is proportional to the strength of a stray electric field. Therefore, we evaluated the micromotion compensation condition by measuring the ion displacements from the ion equilibrium position using two different radial trap frequencies with various combinations of the compensation voltage. The residual electric field uncertainty of this technique reached a few volts per meter. This compensation technique does not depend on the orientation of the incident cooling laser or the detuning and imaging direction. Therefore, this method is suitable for a planar ion trap, a stylus ion trap, which limits the propagation angle of lasers, or miniaturized ion trap systems for sensing and metrological applications.

Tailoring fields of one-sheet and two-sheet planar ion trap mass analyzers

In this paper, a simulation study on tailoring the fields in planar ion trap geometries for making them suitable for mass analysis is presented. Two different planar trap geometries were considered: the first is a One-Sheet Ion Trap Geometry in which the ions are trapped off-plane and the second is a Two-Sheet Ion Trap Geometry in which the ions are trapped in between the two sheets. Both DC and RF potentials were used to trap ions.The fields were tailored to obtain linear trapping fields in these two geometries. This was done by splitting the central electrode into segments and applying suitable DC potentials to them. The potentials were computed using a least square method. The simulations were carried out considering a printed circuit board (PCB) with a Teflon base. The One-Sheet Ion Trap Geometry consists of five electrodes, of which the central electrode is segmented. In Two-Sheet Ion Trap Geometry, each sheet consists of three electrodes, of which the central electrode is segmented.The method outlined in the study is able to tailor fields to be linear as well as mildly superlinear.

Operation of a Microfabricated Planar Ion‐Trap for Studies of a Yb+–Rb Hybrid Quantum System

In order to study interactions of atomic ions with ultracold neutral atoms, it is important to have sub‐µm control over positioning ion crystals. Serving for this purpose, a microfabricated planar ion trap featuring 21 DC electrodes is introduced. The ion trap is controlled by a home‐made FPGA voltage source providing independently variable voltages to each of the DC electrodes. To assure stable positioning of ion crystals with respect to trapped neutral atoms, the authors integrate into the overall design a compact mirror magneto optical chip trap (mMOT) for cooling and confining neutral 87Rb atoms. The trapped atoms will be transferred into an also integrated chip‐based Ioffe‐Pritchard trap potential formed by a Z‐shaped wire and an external bias magnetic field. The authors introduce the hybrid atom–ion chip, the microfabricated planar ion trap, and use trapped ion crystals to determine ion lifetimes, trap frequencies, positioning ions, and the accuracy of the compensation of micromotion.

Extended mass range detection with a microscale planar linear ion trap mass spectrometer

An extended mass range covering m/z 70–240 in a microscale (r0 = 800 μm) planar linear ion trap (μPLIT) is demonstrated, enabled by optimization of dipole resonance ejection conditions without increasing trapping voltage or frequency compared with prior results. This represents a significant increase in the measureable mass range of coplanar traps and microscale traps in general. Performance was demonstrated using headspace vapor of octafluorotoluene (OFT) as well as mixture of perflurotributylamine (PFTBA) and OFT. Typical mass resolution of approximately 3 Da (FWHM) was observed.

A Microscale Planar Linear Ion Trap Mass Spectrometer.

The planar linear ion trap (PLIT) is a version of the two-dimensional linear quadrupole ion trap constructed using two facing dielectric substrates on which electrodes are lithographically patterned. In this article, we present a PLIT that was successfully miniaturized from a radius of 2.5mm to a microscale radius of 800μm (a scaling factor of 3.125). The mathematics concerning scaling an ion trap mass spectrometer are demonstrated-including the tradeoff between RF power and pseudopotential well depth. The time average power for the microscale PLIT is, at best, ~1/100 that of the PLIT but at a cost of potential well depth of ~1/10 the original. Experimental data using toluene/deuterated toluene and isobutylbenze to verify trap performance demonstrated resolutions around 1.5Da at a pressure of 5.4 × 10-3Torr. The microscale PLIT was shown to retain resolutions between 2.3 and 2.7Da at pressures up to 42 × 10-3Torr while consuming a factor of 3.38 less time average power than the unscaled PLIT. Graphical Abstract.

Double resonance ejection using novel radiofrequency phase tracking circuitry in a miniaturized planar linear ion trap mass spectrometer.

Ion trap mass spectrometers are attractive due to their inherent sensitivity and specificity. Miniaturization increases trap portability for in situ mass analysis by relaxing vacuum and voltage requirements but decreases the trapping volume. To overcome signal/resolution loss from miniaturization, double resonance ejection using phase tracking circuitry was investigated. Phase tracking circuitry was developed to induce double resonance ejection in a planar linear ion trap using the β 2/3 hexapole resonance line. Double resonance was observed using phase tracking circuitry. Resolution of 0.5 m/z units and improved signal-to-noise ratio (SNR) compared with AC resonant ejection were achieved. The phase tracking circuitry proved effective despite deviations from a true phase locked condition. Double resonance ejection is a means to increase signal intensity in a miniaturized planar ion trap.

Optimal fabrication methods for miniature coplanar ion traps.

Ion trap mass spectrometers are beneficial due to their intrinsic sensitivity and specificity. Therefore, a portable version for in situ analysis of various compounds is very attractive. Miniaturization of ion traps is paramount for the portability of such mass spectrometers. We developed an optimized design for a planar linear ion trap mass spectrometer, consisting of two trapping plates with photolithographically patterned electrodes. Each plate is constructed using a machined glass substrate and standard microfabrication procedures. The plates are attached to a patterned circuit board via wire bonds then positioned approximately 5mm apart. Trapped ions are detected by ejecting them through tapered slits, which alleviate charge buildup. Mass analysis can be performed through either boundary or resonant ion ejection. Better than unit mass resolution is demonstrated with resonant ejection. The optimized planar linear ion trap provides good resolution and the potential for further miniaturization. This was accomplished by vigorously testing variables associated with ion trap design including electrical connections, substrate materials, and electrode designs.

Measuring Anomalous Heating in a Planar Ion Trap with Variable Ion-Surface Separation.

Cold ions trapped in the vicinity of conductive surfaces experience heating of their oscillatory motion. Typically, the rate of this heating is orders of magnitude larger than expected from electric field fluctuations due to thermal motion of electrons in the conductors. This effect, known as anomalous heating, is not fully understood. One of the open questions is the heating rate's dependence on the ion-electrode separation. We present a direct measurement of this dependence in an ion trap of simple planar geometry. The heating rates are determined by taking images of a single ^{172}Yb^{+} ion's resonance fluorescence after a variable heating time and deducing the trapped ion's temperature from measuring its average oscillation amplitude. Assuming a power law for the heating rate versus ion-surface separation dependence, an exponent of -3.79±0.12 is measured.

Optimization of parameters of a surface-electrode ion trap and experimental study of influences of surface on ion lifetime

In this paper we report the optimal design and fabrication of a gold-on-silica linear segmented surface-electrode ion trap. By optimizing the thickness and width of the electrodes, we improved the trapping ability and trap scalability. By using some practical experimental operation methods, we successfully minimized the trap heating rate. Consequently, we could trap a string of up to 38 ions, and a zigzag structure with 24 ions, and transport two trapped ions to different zones. We also studied the influences of the ion chip surface on the ion lifetime. The excellent trapping ability and flexibility of operation of the planar ion trap shows that it has high feasibility for application in the development a practical quantum information processor or quantum simulator.

Ultraviolet Photodissociation Induced by Light-Emitting Diodes in a Planar Ion Trap.

The first application of light-emitting diodes (LEDs) for ultraviolet photodissociation (UVPD) mass spectrometry is reported. LEDs provide a compact, low cost light source and have been incorporated directly into the trapping cell of an Orbitrap mass spectrometer. MS/MS efficiencies of over 50 % were obtained using an extended irradiation period, and UVPD was optimized by modulating the ion trapping parameters to maximize the overlap between the ion cloud and the irradiation volume.

Ultraviolet Photodissociation Induced by Light‐Emitting Diodes in a Planar Ion Trap

AbstractThe first application of light‐emitting diodes (LEDs) for ultraviolet photodissociation (UVPD) mass spectrometry is reported. LEDs provide a compact, low cost light source and have been incorporated directly into the trapping cell of an Orbitrap mass spectrometer. MS/MS efficiencies of over 50 % were obtained using an extended irradiation period, and UVPD was optimized by modulating the ion trapping parameters to maximize the overlap between the ion cloud and the irradiation volume.

A planar ion trap chip with integrated structures for an adjustable magnetic field gradient

We present the design, fabrication, and characterization of a segmented surface ion trap with integrated current-carrying structures. The latter produce a spatially varying magnetic field necessary for magnetic-gradient-induced coupling between ionic effective spins. We demonstrate trapping of strings of 172Yb+ ions and characterize the performance of the trap and map magnetic fields by radio frequency-optical double-resonance spectroscopy. In addition, we apply and characterize the magnetic gradient and demonstrate individual addressing in a string of three ions using RF radiation.

A Simulation Study of the Planar Electrostatic Ion Trap Mass Analyzer

The Planar electrostatic ion trap expands the trapping space of the linear electrostatic ion trap, giving rise to higher tolerance to space charge. A rotational symmetrical design was made, which has a trapping field between two layers of concentric circular electrodes, and the ions are trapped to oscillate around the center plane between the electrodes. The oscillatory motions of the ions were simulated and the field distribution was optimized to achieve isochronous motion against energy spread in R, z, and φ directions. The image charge signal can be picked up by more than one circular electrode and using FFT the mass resolution for the optimized trap can reach 80,000 FWHM. While Fourier transform of the image charge signal generates many high harmonic peaks, the unwanted harmonic peaks can be eliminated by linear combination of image charge signals from multiple pick-up electrodes to give satisfactory results.

Reduction of heating rate in a microfabricated ion trap by pulsed-laser cleaning

Laser cleaning of the electrodes in a planar micro-fabricated ion trap has been attempted using ns pulses from a tripled Nd:YAG laser at 355 nm. The effect of the laser pulses at several energy density levels has been tested by measuring the heating rate of a single 40Ca+ trapped ion as a function of its secular frequency ωz. A reduction of the electric-field noise spectral density by ∼50% has been observed and a change in the frequency dependence also noticed. This is the first reported experiment where the ‘anomalous heating’ phenomenon has been reduced by removing the source as opposed to reducing its thermal driving by cryogenic cooling. This technique may open up the way to better control of the electrode surface quality in ion microtraps.

Designing spin-spin interactions with one and two dimensional ion crystals in planar micro traps

We discuss the experimental feasibility of quantum simulation with trapped ion crystals, using magnetic field gradients. We describe a micro structured planar ion trap, which contains a central wire loop generating a strong magnetic gradient of about 20 T/m in an ion crystal held about 160 \mu m above the surface. On the theoretical side, we extend a proposal about spin-spin interactions via magnetic gradient induced coupling (MAGIC) [Johanning, et al, J. Phys. B: At. Mol. Opt. Phys. 42 (2009) 154009]. We describe aspects where planar ion traps promise novel physics: Spin-spin coupling strengths of transversal eigenmodes exhibit significant advantages over the coupling schemes in longitudinal direction that have been previously investigated. With a chip device and a magnetic field coil with small inductance, a resonant enhancement of magnetic spin forces through the application of alternating magnetic field gradients is proposed. Such resonantly enhanced spin-spin coupling may be used, for instance, to create Schr\"odinger cat states. Finally we investigate magnetic gradient interactions in two-dimensional ion crystals, and discuss frustration effects in such two-dimensional arrangements.

Coaxial Ion Trap Mass Spectrometer: Concentric Toroidal and Quadrupolar Trapping Regions

We present the design and results for a new radio-frequency ion trap mass analyzer, the coaxial ion trap, in which both toroidal and quadrupolar trapping regions are created simultaneously. The device is composed of two parallel ceramic plates, the facing surfaces of which are lithographically patterned with concentric metal rings and covered with a thin film of germanium. Experiments demonstrate that ions can be trapped in either region, transferred from the toroidal to the quadrupolar region, and mass-selectively ejected from the quadrupolar region to a detector. Ions trapped in the toroidal region can be transferred to the quadrupole region using an applied ac signal in the radial direction, although it appears that the mechanism of this transfer does not involve resonance with the ion secular frequency, and the process is not mass selective. Ions in the quadrupole trapping region are mass analyzed using dipole resonant ejection. Multiple transfer steps and mass analysis scans are possible on a single population of ions, as from a single ionization/trapping event. The device demonstrates better mass resolving power than the radially ejecting halo ion trap and better sensitivity than the planar quadrupole ion trap.

A planar ion trapping microdevice with integrated waveguides for optical detection

A planar ion trap with an integrated waveguide was fabricated and characterized. The microdevice, consisting of a 1 mm-diameter one-hole ring trap and multi-mode optical waveguides, was made on a glass wafer using microfabrication techniques. The experimental results demonstrate that the microdevice can trap 1.5 μm- to 150 μm-diameter charged particles in air under an alternating electric field with the amplitude and frequency varying from 100 V to 750 V, and 100 Hz to 700 Hz, respectively. The on-chip waveguide is capable of detecting the presence of a particle in the trap, and the particle secular motion frequency was found to depend on the input alternating signal amplitude and frequency.

Modeling ion trap thermal noise decoherence

We present a detailed analysis of ion heating caused by thermal fluctuation noise in ion traps. The results of the analysis are used to estimate thermal noise ion heating rates for a variety of trap electrode configurations and materials, including recent scalable multiplexed planar ion trap proposals based on silicon VLSI technology. We find that minimizing thermal noise ion heating places severe constraints on the design and materials used for ion traps.