Electrode Ion Trap Research Articles

Research on double resonant excitation in a triangular electrode ion trap with asymmetric geometry.

The triangular electrode linear ion trap with asymmetric geometry has been reported to possess a high ion unidirectional ejection efficiency and a reasonable mass resolution. To further improve its performance, a double resonant excitation method involving a dipolar and a quadrupolar resonant excitation was applied here. The dipolar excitation method was carried out by applying a supplementary alternating voltage out of phase to one pair of the electrodes, whereas the quadrupolar excitation (QE) method was carried out by adding a supplementary alternating voltage in phase to another pair of electrodes. Numerical simulations were performed to explore the impact of the frequency difference between the alternating current (AC) and the QE voltage (∆ω), the frequency of the AC voltage (ωAC), and the QE voltage amplitude (VQE). The mass resolution could be improved to ~4700 , which was approximately twice compared to that with only dipolar resonant excitation, and the ion unidirectional ejection efficiency could be improved to 97%. Even with a high scan rate of 6000 Da/s, there was minimal loss of mass resolution caused by increased scan rate in double resonant excitation mode. By employing the double resonant excitation method, the mass resolution could be further increased while maintaining a considerably high ion unidirectional ejection efficiency, which might be a simple and practical approach for developing a high-performance miniature ion trap mass analyzer.

Surface-Electrode Ion Trap Development

We present a segmented linear surface electrode ion trap design that can be used for various applications in optical clocks and quantum computation based on trapped 171Yb+ ions. Our simulations show that calculated trap depth can reach up to several electronvolts and that the pseudopotential minimum of the trap is located above the trap surface at a distance greater than 80 μm. The described pseudopotential simulations and calculations of different trap parameters can be used to design the planar trap with required parameters. This design could be scaled to store a long chain of ions and used for quantum logic applications as well.

Surface-electrode ion trap design for near-field microwave quantum gates

We present a design study into an ion trap electrode geometry for applying near-field microwave two-qubit gates. This design features an ‘S’-shaped meander electrode to passively null the microwave field. It has ground planes separating the meander electrode from all of the DC and single-qubit microwave electrodes, which should reduce the sensitivity of the microwave field distribution to the boundary conditions of these electrodes. We show that it is possible to design a single-layer trap with this geometry such that the simulated microwave field null overlaps with the RF field null, and that the positions of these nulls can be simulated to a precision of 100 nm with moderate computing resources. We also show that such a trap can be designed such that ion chains can be trapped, transported and split with feasible DC and RF voltages. While this particular design is optimized for ^{43}Ca^{+} ions, our approach could be applied to other ions by changing the microwave frequency to match the corresponding qubit transition frequency.

Direct Coupling of Methane and Carbon Dioxide on Tantalum Cluster Cations.

Understanding molecular-scale reaction mechanisms is crucial for the design of modern catalysts with industrial prospect. Through joint experimental and computational studies, we investigate the direct coupling reaction of CH4 and CO2 , two abundant greenhouse gases, mediated by Ta1,4 + ions to form larger oxygenated hydrocarbons. Coherent with proposed elementary steps, we expose products of CH4 dehydrogenation [Ta1,4 CH2 ]+ to CO2 in a ring electrode ion trap. Product analysis and reaction kinetics indicate a predisposition of the tetramers for C-O coupling with a conversion to products of CH2 O, whereas atomic cations enable C-C coupling yielding CH2 CO. Selected experimental findings are supported by thermodynamic computations, connecting structure, electronic properties, and catalyst function. Moreover, the study of bare Ta1,4 + compounds indicates that methane dehydrogenation is a significant initial step in the direct coupling reaction, enabling new, yet unknown reaction pathways.

Fabrication of surface ion traps with integrated current carrying wires enabling high magnetic field gradients

A major challenge for quantum computers is the scalable simultaneous execution of quantum gates. One approach to address this in trapped ion quantum computers is the implementation of quantum gates based on static magnetic field gradients and global microwave fields. In this paper, we present the fabrication of surface ion traps with integrated copper current carrying wires embedded inside the substrate below the ion trap electrodes, capable of generating high magnetic field gradients. The copper layer’s measured sheet resistance of 1.12 mΩ/sq at room temperature is sufficiently low to incorporate complex designs, without excessive power dissipation at high currents causing a thermal runaway. At a temperature of 40 K the sheet resistance drops to 20.9 μΩ/sq giving a lower limit for the residual resistance ratio of 100. Continuous currents of 13 A can be applied, resulting in a simulated magnetic field gradient of 144 T m−1 at the ion position, which is 125 μm from the trap surface for the particular anti-parallel wire pair in our design.

Thermal deformation analysis of a 3D printed Kingdon ion trap for the Moon environment

Soil analysis is a significant part of space exploration. Nowadays, great attention is given to soil investigation on the Moon, and special missions are being planned to carry out analyses of lunar soil in situ (Valero et al., 2007). Mass spectrometry is a proven method that is commonly used for identifying the chemical composition of the soil. One of the best candidates for a mass spectrometer for this purpose is a mass spectrometer based on an ion trap, which has high mass resolution, a low weight, a compact size, and low power consumption. Among the existing ion traps (Kingdon traps, Penning traps, Radiofrequency Paul traps, and Radiofrequency linear traps), a Kingdon trap of unique design would be a viable option for many applications.However, disturbances in the space environment negatively affect the use of an ion trap. One of these harmful effects in the lunar environment is the wide range of temperatures. Heating or cooling causes deformation of the geometry of the ion trap electrodes, reducing the accuracy of the measurements.The current research aims to compare metal and ceramic ion traps and to investigate how the material used in manufacturing affects the performance of the mass spectrometer. Analysis of thermally-induced deformations was used as the primary method of the research. We manufactured models of metal and ceramic ion traps, analyzed the effects of electrode deformation on the analytical characteristics of the mass spectrometer, conducted thermal deformation analysis, and validated our results.The ceramic ion trap (56.3 µm) shows less thermal deformation in comparison with the metal one (105.5 µm). The thermal expansion that is higher than 50 µm significantly affects the performance of the instrument. The loss time of the signal decreased twice reduces the resolution of the ion trap also by a factor of two. We propose introducing corrections to the shape of the surface that electrodes have at room temperature so that after thermal compression at 97 K (average temperature of the Moon Polar regions), the surface has a shape corresponding to the ideal performances of the instrument.

An efficient method for producing 9Be+ ions using a 2 + 1 resonance-enhanced multiphoton ionization process

We report a method of creating pure 9Be+ ions by a 2 + 1 resonance-enhanced multiphoton ionization for the ionization potential of 75 192.64(6) cm−1 (133 nm). The efficient generation of 9Be+ ions has been realized in a segmented linear ion trap. The average loading rates with a 10 ns, 1 mJ laser at 310 nm and 306 nm are 3.8 and 1.3 ions per pulse, respectively. This method has the advantage of reducing the electron contamination to the ion trap electrodes greatly. It also reduces the requirement of single-photon energy while satisfying the need for ionization probability and can be applied to other atoms with high ionization thresholds.

Generation of a single-ion large oscillator

We demonstrate the generation of a trapped ion oscillator having large oscillation amplitude of $16.9~{\rm \mu m}$. Applying an offset voltage to the ion trap electrode helped achieve a displacement of the trap center within the time scale of 5 ns. The fluorescence dynamics of the ion were analyzed after the displacement to estimate the oscillation amplitude. The realized trap displacement is one order magnitude larger than that achieved in the previous work. Thus, this result is an important step toward the realization of a gyroscope using a single trapped ion.

RF Performance Benchmarking of TSV Integrated Surface Electrode Ion Trap for Quantum Computing

Surface electrode ion trap is highly promising for practical quantum computing due to its superior controllability on the trapped ions. With advanced microfabrication techniques, silicon has been developed as an ion trap substrate for delicate surface electrodes design and monolithic electro-optical components integration. However, the high RF loss of silicon hinders the possible large-scale implementation. In this work, we demonstrate a through silicon via (TSV) integrated ion trap, which has low RF loss due to the elimination of wire bonding (WB) pads on the surface and the miniaturization of form factor. We also fabricate two types of conventional WB traps with or without a grounding screen layer. The RF performances of different ion traps are tested and compared, in terms of on-chip S-parameter, postpackaging resonance, and resulting power loss. The results show that the TSV trap has low S21 (~0.2 dB at 50 MHz), high <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> factor (~22), and low power loss (0.26 W) compared to WB traps. In addition, 3-D finite element modeling (FEM) is employed for electric field visualization and RF loss analysis of different traps. The extracted results from the modeling show a decent agreement with the measurements. In addition to various RF tests, the design, fabrication, and ion trapping operation of different ion traps are presented. This work provides insights into RF loss of ion trapping devices and offers a new solution for RF loss reduction.

(Invited) 3D Integration of Surface Electrode Ion-Trap on Silicon and Glass Substrates for Quantum Information Processing

Surface electrode ion trap is a promising candidate for quantum information processing (QIP), due to its feasibilities towards large-scale fabrication. There are several important considerations for the realization of surface ion trap including choices of substrate and interconnections. In this paper, surface electrode ion traps on different substrates (e.g., high-resistivity silicon, silicon with ground plane and glass) are fabricated, assembled and tested. To simultaneously leverage the established fabrication technique of silicon and superior insulation property of glass, we further demonstrate a novel ion trap design with heterogenous integration of silicon and glass, acting respectively as ion trap and interposer substrates. The vertical connection between the silicon ion trap and the glass interposer is achieved by through silicon via (TSV) and micro bump. This combination demonstrates promising RF and trapping properties.Standard back end of line CMOS process is used for the fabrication of ion traps on both silicon and glass substrates. With 12-inch silicon/glass wafers, ~2,000 traps with different design dimensions can be fabricated simultaneously. For ion trap on high-resistivity silicon substrate (HR trap, Fig. 1(a)), lithography-defined electroplating of 3.7 µm Cu with Au finish is conducted on top of 3 µm patterned SiO2 layer. For ion trap on silicon with grounding plane (GND trap, Fig. 1(b)), 1 µm Cu damascene process is used to form the meshed grounding plane that shields silicon substrate from RF signal penetration. For ion trap on glass substrate (glass trap, Fig. 1(c)), Cu and Au can be directly electroplated onto glass substrate after adhesion and seed layers deposition. To evaluate the RF performance of various traps, S parameter measurement and resonator test are conducted. Glass trap features extremely low RF loss as compared to silicon counterparts.Heterogenous integration of silicon ion trap and glass interposer with TSV interconnections (TSV trap, Fig. 1(d)) is thus proposed, in which the possibility of integration with electronics (DACs) components is preserved on the silicon ion trap chip, whereas the RF performance of the entire device can be guaranteed by the glass interposer. As shown in Fig. 1(e) and (f), integrated photonics passive components such as grating couplers can be implemented into the silicon trap chip for ion addressing with laser. Additional grounding layer with designed openings on top of grating couplers is introduced to further minimize RF loss. 88Sr+ ions are successfully trapped on both glass and TSV traps.In summary, this work discusses the performance of ion traps on various substrates and demonstrates the silicon-glass integrated system to enable the scalability of surface electrode ion trap. The work was supported by A*STAR Quantum Technology for Engineering (A1685b0005). Figure 1

Surface science motivated by heating of trapped ions from the quantum ground state

For the past two and a half decades, anomalous heating of trapped ions from nearby electrode surfaces has continued to demonstrate unexpected results. Caused by electric-field noise, this heating of the ions’ motional modes remains an obstacle for scalable quantum computation with trapped ions. One of the anomalous features of this electric-field noise is the reported nonmonotonic behavior in the heating rate when a trap is incrementally cleaned by ion bombardment. Motivated by this result, the present work reports on a surface analysis of a sample ion-trap electrode treated similarly with incremental doses of Ar+ ion bombardment. Kelvin probe force microscopy and x-ray photoelectron spectroscopy were used to investigate how the work functions on the electrode surface vary depending on the residual contaminant coverage between each treatment. It is shown that the as-fabricated Au electrode is covered with a hydrocarbon film that is modified after the first treatment, resulting in work functions and core-level binding energies that resemble that of atomic-like carbon on Au. Changes in the spatial distribution of work functions with each treatment, combined with a suggested phenomenological coverage and surface-potential roughness dependence to the heating, appear to be related to the nonmonotonic behavior previously reported.

Room-Temperature Methane Activation Mediated by Free Tantalum Cluster Cations: Size-by-Size Reactivity.

The energetics of small cationic tantalum clusters and their gas-phase adsorption and dehydrogenation reaction pathways with methane are investigated with ion-trap experiments and spin-density-functional-theory calculations. Tan+ clusters are exposed to methane under multicollision conditions in a cryogenic ring electrode ion-trap. The cluster size affects the reaction efficiency and the number of consecutively dehydrogenated methane molecules. Small clusters (n = 1-4) dehydrogenate CH4 and concurrently eliminate H2, while larger clusters (n > 4) demonstrate only molecular adsorption of methane. Unique behavior is found for the Ta+ cation, which dehydrogenates consecutively up to four CH4 molecules and is predicted theoretically to promote formation of a [Ta(CH2-CH2-CH2)(CH2)]+ product, exhibiting C-C coupled groups. Underlying mechanisms, including reaction-enhancing couplings between potential energy surfaces of different spin-multiplicities, are uncovered.

A cryogenic single nanoparticle action spectrometer.

A nanoparticle (NP) mass spectrometer designed to perform action spectroscopy on single NPs at cryogenic temperatures is described. NPs from an electrospray ion source with masses ranging from 460 to 740 MDa are injected and trapped in a temperature controllable (8-350 K) split-ring electrode ion-trap characterized by improved optical access and trapping potential. After excess NPs are ejected from the trap, the mass-to-charge ratio and subsequently the absolute mass of the trapped NP are determined nondestructively using Fourier transformation and resonant excitation methods. The setup allows us to monitor the mass variation of a single NP as a function of the ion-trap temperature, collision-gas pressure, and irradiation laser power. Ion-trap temperature controlled N2 adsorption at cryogenic temperatures onto a single, ∼90 nm diameter SiO2 NP is demonstrated and characterized. We further show that laser irradiation at 532 nm leads to power-dependent changes in the effective N2 adsorption rate of the particle, which can be monitored and ultimately exploited to measure absorption spectra of a single NP.

Efficient isotope-selective pulsed laser ablation loading of 174Yb+ ions in a surface electrode trap.

We report a highly efficient loading of 174Yb+ ions in a surface electrode ion trap by using single pulses from a Q-switched Nd:YAG laser to ablate neutral atoms, combined with a two-photon photo-ionization process. The method is three orders of magnitude faster to load a single ion as compared to traditional resistively heated sources and can load large collections of ions in seconds. The negligible thermal load of this method enables the use of this ablation-based loading scheme in ion traps operating under cryogenic conditions.

Crystallographic orientation dependence of work function: carbon adsorption on Au surfaces

We investigate the work function (WF) variation of different Au crystallographic surface orientations with carbon atom adsorption. Ab initio calculations within density-functional theory are performed on carbon deposited (100), (110), and (111) gold surfaces. The WF behaviour with carbon coverage for the different surface orientations is explained by the resultant electron charge density distributions. The dynamics of carbon adsorption at sub-to-one- monolayer (ML) coverage depends on the landscape of the potential energy surfaces. At higher ML coverage, because of adsorption saturation, the WF will have weak surface orientation dependence. This systematic study has consequential bearing on studies of electric-field noise emanating from polycrystalline gold ion-trap electrodes that have been largely employed in microfabricated electrodes.

Evidence for multiple mechanisms underlying surface electric-field noise in ion traps

Electric-field noise from ion-trap electrode surfaces can limit the fidelity of multiqubit entangling operations in trapped-ion quantum information processors and can give rise to systematic errors in trapped-ion optical clocks. The underlying mechanism for this noise is unknown, but it has been shown that the noise amplitude can be reduced by energetic ion bombardment, or "ion milling," of the trap electrode surfaces. Using a single trapped $^{88}$Sr$^{+}$ ion as a sensor, we investigate the temperature dependence of this noise both before and after ex situ ion milling of the trap electrodes. Making measurements over a trap electrode temperature range of 4 K to 295 K in both sputtered niobium and electroplated gold traps, we see a marked change in the temperature scaling of the electric-field noise after ion milling: power-law behavior in untreated surfaces is transformed to Arrhenius behavior after treatment. The temperature scaling becomes material-dependent after treatment as well, strongly suggesting that different noise mechanisms are at work before and after ion milling. To constrain potential noise mechanisms, we measure the frequency dependence of the electric-field noise, as well as its dependence on ion-electrode distance, for niobium traps at room temperature both before and after ion milling. These scalings are unchanged by ion milling.

Structure and Performance of Polygonal Electrode Linear Ion Trap

Abstract The polygonal electrode linear ion trap (PeLIT) can produce quadrupolar electric field plus some higher order field, which balances the relationship between mass resolution and electrode manufacturing difficulties. The electrodes of PeLIT are relatively simple, but have a good mass resolving power. This study investigated the relationship between the electric field distribution and the ion trap structures, and the performances of PeLIT through theoretical simulation and experimental study. Research results of simulation showed that the polygonal electrode linear ion traps with different structures had different electric field distributions and mass analysis performances. The negative decapole field distorted the performances significantly. The experimental results showed that the mass resolution of reserpine ions (m/z 609) was more than 2500 using a polygonal electrode ion trap. At the same time, mass selective excitation and tandem mass spectrometry experiments were also carried.

Geometric optimization of toroidal ion trap based on electric field analysis and SIMION simulation

The toroidal-cylindrical ion trap (TCIT) is a small multi-function tandem ion trap analyzer with a simple structure and a compact design. The asymmetric structure of the out toroidal ion trap (T-trap) confers the in-trap region with a non-uniform electric field distribution, particularly when a plate ring electrode is used. To optimize the electric field distribution in the trap, the shapes of the toroidal electrodes were modified to compensate for the electric field. For this purpose, we developed a simple simulation-based method for evaluating the optimized asymmetric structure of the ion trap electrode. Specifically, static electric field distribution in the trap was acquired using COMSOL software and then simply analyzed, while the SIMION simulation platform was adopted to characterize both the ion motion and the performance of the T-trap with an modified structure. The results revealed that electrode optimization can not only improve the non-uniformity of the in-trap electric field distribution but also implement unidirectional emission of the ions upon resonance excitation, thereby significantly increasing the utilization efficiency of the ions in TCIT. In addition, a high correlation was found between the electric field gradient distribution in the trap and the ion emission characteristics, which can provide an simple but useful guiding significance for the performance and structural optimization of T-trap.

Automating quantum experiment control

The field of quantum information processing is rapidly advancing. As the control of quantum systems approaches the level needed for useful computation, the physical hardware underlying the quantum systems is becoming increasingly complex. It is already becoming impractical to manually code control for the larger hardware implementations. In this chapter, we will employ an approach to the problem of system control that parallels compiler design for a classical computer. We will start with a candidate quantum computing technology, the surface electrode ion trap, and build a system instruction language which can be generated from a simple machine-independent programming language via compilation. We incorporate compile time generation of ion routing that separates the algorithm description from the physical geometry of the hardware. Extending this approach to automatic routing at run time allows for automated initialization of qubit number and placement and additionally allows for automated recovery after catastrophic events such as qubit loss. To show that these systems can handle real hardware, we present a simple demonstration system that routes two ions around a multi-zone ion trap and handles ion loss and ion placement. While we will mainly use examples from transport-based ion trap quantum computing, many of the issues and solutions are applicable to other architectures.

Measurements of trapped-ion heating rates with exchangeable surfaces in close proximity

ABSTRACTElectric-field noise from the surfaces of ion-trap electrodes couples to the ion’s charge causing heating of the ion’s motional modes. This heating limits the fidelity of quantum gates implemented in quantum information processing experiments. The exact mechanism that gives rise to electric-field noise from surfaces is not well-understood and remains an active area of research. In this work, we detail experiments intended to measure ion motional heating rates with exchangeable surfaces positioned in close proximity to the ion, as a sensor to electric-field noise. We have prepared samples with various surface conditions, characterized in situ with scanned probe microscopy and electron spectroscopy, ranging in degrees of cleanliness and structural order. The heating-rate data, however, show no significant differences between the disparate surfaces that were probed. These results suggest that the driving mechanism for electric-field noise from surfaces is due to more than just thermal excitations alone.