Micro-fabricated stylus ion trap

Physical Review B

We aim to illuminate how the microscopic properties of a metal surface map to its electric-field noise characteristics. In our system, prolonged heat treatments of a metal film can induce a rise in the magnitude of the electric-field noise generated by the surface of that film. We refer to this heat-induced rise in noise magnitude as a thermal transformation. The underlying physics of this thermal transformation process is explored through a series of heating, milling, and electron treatments performed on a single surface ion trap. Between these treatments, 40 Ca + ions trapped 70 µm above the surface of the metal are used as detectors to monitor the electric-field noise at frequencies close to 1 MHz. An Auger spectrometer is used to track changes in the composition of the contaminated metal surface. With these tools we investigate contaminant deposition, chemical reactions, and atomic restructuring as possible drivers of thermal transformations. The data suggest that the observed thermal transformations can be explained by atomic restructuring at the trap surface. We hypothesize that a rise in local atomic order increases surface electric-field noise in this system.

Applied Physics B, 2016

We present a new single-ion endcap trap for high precision spectroscopy that has been designed to minimize ion-environment interactions. We describe the design in detail and then characterize the working trap using a single trapped 171 Yb + ion. Excess micromotion has been eliminated to the resolution of the detection method and the trap exhibits an anomalous phonon heating rate of d n /dt = 24 +30 −24 s −1. The thermal properties of the trap structure have also been measured with an effective temperature rise at the ion's position of ∆T (ion) = 0.14 ± 0.14 K. The small perturbations to the ion caused by this trap make it suitable to be used for an optical frequency standard with fractional uncertainties below the 10 −18 level.

Anomalous heating of trapped atomic ions is a major obstacle to their use as quantum bits in a scalable quantum computer. The physical origin of this heating is not fully understood, but experimental evidence suggests that it is caused by electric-field noise emanating from the surface of the trap electrodes. In this study, we have investigated the role that adsorbates on the electrodes play by identifying contaminant overlayers, developing an in situ argon-ion beam cleaning procedure, and measuring ion heating rates before and after cleaning the trap electrodes' surfaces. We find a reduction of two orders of magnitude in heating rate after cleaning.

Physical Review A, 2010

We present a model as well as experimental results for a surface electrode radio-frequency Paul trap that has a circular electrode geometry well-suited for trapping of single ions and two-dimensional planar ion crystals. The trap design is compatible with microfabrication and offers a simple method by which the height of the trapped ions above the surface may be changed in situ. We demonstrate trapping of single 88 Sr + ions over an ion height range of 200-1000µm for several hours under Doppler laser cooling, and use these to characterize the trap, finding good agreement with our model.

2010

Ion traps provide an excellent tool for controlling and observing the state of a single trapped ion. For this reason, ion traps have been proposed as a possible system for large-scale quantum computation. However, many obstacles must be overcome before quantum computing can become a reality. In particular, perturbations in the electric field due to noise and electrode charging must be reduced to increase coherence of the motional quantum state. Gold has been a popular choice in the past due to its inert properties; however, it is undesireable due its incompatibility with CMOS technology. This has led to increased research into alternative CMOS-compatible materials, such as aluminum and copper. This thesis presents measurements of electric field noise and light-induced charging in aluminum, copper, and gold surface electrode traps. In addition, the effect of oxide growth on field noise and electrode charging is explored by controlling the thickness of aluminum oxide on several aluminum traps. The measurements show that electric field noise can be suppressed in aluminum traps to approximately 10-18 V 2 cm-2 Hz-1, matching the noise exhibited in gold traps, and that copper traps exhibit noise within an order of magnitude of that in aluminum and gold. However, the natural oxide of aluminum poses many problems towards high-performance aluminum ion traps. The electric field noise is shown to be strongly dependent on the oxide thickness, increasing the noise by a factor of about 10 until saturation at a thickness of 13 nm. Charging of surface electrodes is shown to be highly dependent upon the material, but the model presented does not match the experimental data and is found to be incomplete. These results indicate that ion traps made out of CMOS-compatible materials can perform as well as more traditional traps fabricated from gold with respect to heating and charging as long as methods are developed for controlling oxide growth.

Physical Review B, 2014

We use a single-ion electric-field noise sensor in combination with in situ surface treatment and analysis tools, to investigate the relationship between electric-field noise from metal surfaces in vacuum and the composition of the surface. These experiments are performed in a setup that integrates ion trapping capabilities with surface analysis tools. We find that treatment of an aluminum-copper surface with energetic argon ions significantly reduces the level of room-temperature electric-field noise, but the surface does not need to be atomically clean to show noise levels comparable to those of the best cryogenic traps. The noise levels after treatment are low enough to allow fault-tolerant trapped-ion quantum information processing on a microfabricated surface trap at room temperature.

Physical Review A, 2019

We probe electric-field noise near the metal surface of an ion trap chip in a previously unexplored high-temperature regime. We observe a non-trivial temperature dependence with the noise amplitude at 1-MHz frequency saturating around 500 K. Measurements of the noise spectrum reveal a 1/f α≈1-dependence and a small decrease in α between low and high temperatures. This behavior can be explained by considering noise from a distribution of thermally-activated two-level fluctuators with activation energies between 0.35 eV and 0.65 eV. Processes in this energy range may be relevant to understanding electric-field noise in ion traps; for example defect motion in the solid state and surface adsorbate binding energies. Studying these processes may aid in identifying the origin of excess electric-field noise in ion traps-a major source of ion motional decoherence limiting the performance of surface traps as quantum devices.

Review of Scientific Instruments, 2007

A description of the design and microfabrication of arrays of micrometer-scale cylindrical ion traps is offered. Electrical characterization and initial ion trapping experiments with a massively parallel array of 5 m internal radius ͑r 0 ͒ sized cylindrical ion traps ͑CITs͒ are also described. The ion trap, materials, and design are presented and shown to be critical in achieving minimal trapping potential while maintaining minimal power consumption. The ion traps, fabricated with metal electrodes, have inner radii of 1, 2, 5, and 10 m and range from 5 to 24 m in height. The electrical characteristics of packaged ion trap arrays were measured with a vector network analyzer. The testing focused on trapping toluene ͑C 7 H 8 ͒, mass 91, 92, or 93 amu, in the 5 m sized CITs. Ions were formed via electron impact ionization and were ejected by turning off the rf voltage applied to the ring electrode; a current signal was collected at this time. Optimum ionization and trapping conditions, such as a sufficient pseudopotential well and high ionization to ion loss rate ratio ͑as determined by simulation͒, proved to be difficult to establish due to the high device capacitance and the presence of exposed dielectric material in the trapping region. However, evidence was obtained suggesting the trapping of ions in 1%-15% of the traps in the array. These first tests on micrometer-scale CITs indicated the necessary materials and device design modifications for realizing ultrasmall and low power ion traps.

Journal of Applied Physics, 2011

Electrical charging of metal surfaces due to photoelectric generation of carriers is of concern in trapped ion quantum computation systems, due to the high sensitivity of the ions' motional quantum states to deformation of the trapping potential. The charging induced by typical laser frequencies involved in Doppler cooling and quantum control is studied here, with microfabricated surface-electrode traps made of aluminum, copper, and gold, operated at 6 K with a single Sr þ ion trapped 100 lm above the trap surface. The lasers used are at 370, 405, 460, and 674 nm, and the typical photon flux at the trap is 10 14 photons/cm 2 /sec. Charging is detected by monitoring the ion's micromotion signal, which is related to the number of charges created on the trap. A wavelength and material dependence of the charging behavior is observed: Lasers at lower wavelengths cause more charging, and aluminum exhibits more charging than copper or gold. We describe the charging dynamic based on a rate-equation approach. V

HAL (Le Centre pour la Communication Scientifique Directe), 2023

We report on the progress on a single-ion optical clock that is being developed at the FEMTO-ST institute. Our objective is to reach a fractional frequency stability of the order of 10 -14 at one second for a total volume well below 500 L . The experimental setup is based on a surface electrode single-ion trap. A new trapping chip was designed and produced at the local cleanroom facility, using deep reactive-ion etching (DRIE) on a silicon on insulator-(SOI) wafer. Paul traps require a source of highly-stable and low noise voltage in the radio-frequency (RF) domain. A resonator of our own design has been used to supply high voltage to the trap. We have developed and implemented techniques for 3D micromotion reduction in order to minimize the 2 nd order Doppler shift. Indeed, for Yb + optical spectroscopy, second order Doppler shift and Stark shift due to the ac fields can contribute significantly to the uncertainty budget. We will present the latest results of the trap characterization, which should include lifetime and heating rate measurements of the trap.

Nature Physics, 2006

he electromagnetic manipulation of isolated atoms has led to many advances in physics, from laser cooling 1 and Bose-Einstein condensation of cold gases 2 to the precise quantum control of individual atomic ions 3 . Work on miniaturizing electromagnetic traps to the micrometre scale promises even higher levels of control and reliability 4 . Compared with 'chip traps' for confining neutral atoms 5-7 , ion traps with similar dimensions and power dissipation offer much higher confinement forces and allow unparalleled control at the single-atom level. Moreover, ion microtraps are of great interest in the development of miniature mass-spectrometer arrays 8 , compact atomic clocks 9 and, most notably, large-scale quantum information processors 10,11 . Here we report the operation of a micrometre-scale ion trap, fabricated on a monolithic chip using semiconductor micro-electromechanical systems (MEMS) technology. We confine, laser cool and measure heating of a single 111 Cd + ion in an integrated radiofrequency trap etched from a doped gallium-arsenide heterostructure. Current ion-trap research is largely driven by the quest to build a quantum information processor , where quantum bits (qubits) of information are stored in individual atomic ions and connected through a common interaction with a phonon or photon field. The fundamental experimental requirements for quantum processing have all been met with ion traps, including demonstrations of multi-qubit quantum gates and small algorithms . Effort in this area is now focused on the scaling of ion traps to host much larger numbers of qubits, perhaps by shuttling individual atoms through a complex maze of ion-trap electrodes . The natural host for such a scalable system is an integrated ion-trap chip. We confine single 111 Cd + qubit ions in a radiofrequency linear ion trap 3,19 on a chip by applying a combination of static and oscillating electric potentials to integrated electrodes 20 . The electrodes are lithographically patterned from a monolithic semiconductor substrate, eliminating the need for manual assembly and alignment of individual electrodes. The scaling of this structure to hundreds or thousands of electrodes thus seems possible with existing semiconductor fabrication technology. Candidate linear ion-trap geometries amenable to microfabrication include (i) symmetric high-aspect-ratio multilayer structures with electrodes surrounding the ions 20 , and (ii) asymmetric planar structures with the ions residing above a

2011

We use a single ion as an movable electric field sensor with accuracies on the order of a few V/m. For this, we compensate undesired static electric fields in a planar RF trap and characterize the static fields over an extended region along the trap axis. We observe a strong buildup of stray charges around the loading region on the trap resulting in an electric field of up to 1.3 kV/m at the ion position. We also find that the profile of the stray field remains constant over a time span of a few months.

The European Physical Journal D, 2001

Frequency standard applications and ultra-high resolution spectroscopy of a confined single ion require traps of drastically reduced dimensions (about or below 1 mm). These small dimensions increase the sensitivity of the trapping behavior to imperfections in the trap geometry and to patch potentials. For the aim of the metrological laser interrogation of a single Ca + ion, a miniature cylindrical ring trap was built. In order to optimize the laser cooling process and to reach strong binding conditions, the boundaries of the stability diagram and the zones of low confinement as well as the ion motion properties were characterized.

Nanotechnology, 2008

We found by molecular dynamics simulations that a low energy ion can be trapped effectively in a nanoscale Paul trap in both vacuum and aqueous environment when appropriate AC/DC electric fields are applied to the system. Using the negatively charged chlorine ion as an example, we show that the trapped ion oscillates around the center of the nanotrap with the amplitude dependent on the parameters of the system and applied voltages. Successful trapping of the ion within nanoseconds requires electric bias of GHz frequency, in the range of hundreds of mV. The oscillations are damped in the aqueous environment, but polarization of water molecules requires application of higher voltage biases to reach improved stability of the trapping. Application of a supplemental DC driving field along the trap axis can effectively drive the ion off the trap center and out of the trap, opening a possibility of studying DNA and other charged molecules using embedded probes while achieving a full control of their translocation and localization in the trap.

Journal of Optoelectronics and Advanced Materials, 2008

Physicists have always focused on designing and implementing methods which would eventually allow them to confine and levitate a particle in a well defined region in space, under conditions of minimal perturbations, in an almost interaction free environment. This led to the development of radically new techniques for trapping atomic particles. One major advantage of such a system lies in the fact that the apparatus used to prepare and manipulate atomic quantum states is already in place. It has been refined and developed for high precision spectroscopy, quantum logic and high accuracy frequency standards. This paper deals with optimization of ion trap geometries which are widely used in modern physics.