A Silicon Surface Ion-Trap Chip with Dielectric Sidewalls Shielded by Metal Films

Abstract

An ion trap is a device to confine charged particles by utilizing electromagnetic fields. Since the trapped ions have a feasibility of the individual state manipulation, a long coherence time, and an ideal isolation from the surroundings, the ion-trap technology becomes one of the leading candidates for the physical implementation of quantum information processing. In order to build a large-scale integrated ion-trap system for realizing complex quantum algorithms, microfabrication technologies have been applied to construct ion traps. The use of micro-electro-mechanical system (MEMS) ion-trap chip allows a scalable architecture of ion-trap arrays and integration of functional components to the trap chip, but a few side effects also arise. One of the most particular problems is stray fields generated by the charges accumulated on the sidewalls of thick dielectric pillars or the native oxide grown on metal surfaces, since the stray fields lead to ion micromotions which can cause heating and escape of the trapped ions. This dissertation presents a silicon surface ion-trap chip with dielectric sidewalls shielded by metal films. The oxide pillars supporting the top electrodes are fabricated to have overhang structures, and the upper and lower part of the pillars are coated by separate aluminum layers which are electrically isolated from each other. In order to evaluate the effects of the native metal oxide on the electrode surface to the charging phenomenon, a trap chip with an additional gold layer on the aluminum electrodes is also fabricated. An ultra-high vacuum (UHV) chamber, electrical connections, and an optical setup are prepared to trap 174Yb+ ions, and the ions are successfully trapped by using the experimental setup including the fabricated ion-trap chip. To evaluate the effectiveness of the proposed electrode structures, charging is intentionally induced on the chip surface by injecting a 355-nm pulse laser with 40-μW power perpendicularly to the chip surface. The intensity of the stray field is estimated by measuring the displacement of ion position after charging is induced. When the Al-based chips with exposed and Al-coated dielectric sidewalls are used, the standard deviation of the intensities of stray fields are 3.53, and 5.63 V/m, respectively. However, the standard deviation of the intensity of stray fields in the case of using Au-coated chip is 1.56 V/m, and any stray field is measured when the laser was injected on the surface or sidewalls of the gold-coated electrodes. These experimental results indicate that the gold coating on the surface of the aluminum electrodes and the sidewalls of dielectric pillars is effective for eliminating the generation of stray fields induced by static charges.