Ion transport in macroscopic RF linear traps

Efficient transport of cold atoms or ions is a subject of increasing concern in many experimental applications reaching from quantum information processing to frequency metrology. For the scalable quantum computer architectures based on the shuttling of individual ions, different transport schemes have been developed, which allow to move single atoms minimizing their energy gain. In this article we discuss the experimental implementation of the transport of a three-dimensional ion cloud in a macroscopic linear radiofrequency (RF) trap. The present work is based on numerical simulations done by molecular dynamics taking into account a realistic experimental environment. The deformation of the trapping potential and the spatial extension of the cloud during transport appears to be the major source of the ion energy gain. The efficiency of transport in terms of transfer probability and ion number is also discussed

Fast and efficient transport of large ion clouds

The manipulation of trapped charged particles by electric fields is an accurate, robust and reliable technique for many applications or experiments in high-precision spectroscopy. The transfer of the ion sample between multiple traps allows the use of a tailored environment in quantum information, cold chemistry, or frequency metrology experiments. In this article, we experimentally study the transport of ion clouds of up to 50 000 ions. The design of the trap makes ions very sensitive to any mismatch between the assumed electric potential and the actual local one. Nevertheless, we show that being fast (100 $\mu$s to transfer over more than 20 mm) increases the transport efficiency to values higher than 90 %, even with a large number of ions. For clouds of less than 2000 ions, a 100 % transfer efficiency is observed

Coherent internal state transfer by three-photon STIRAP-like scheme for many-atom samples

A STIRAP-like scheme is proposed to exploit a three-photon resonance taking place in alkaline-earth-metal ions. This scheme is designed for state transfer between the two fine structure components of the metastable D-state which are two excited states that can serve as optical or THz qu-bit. The advantage of a coherent three-photon process compared to two-photon STIRAP lies in the possibility of exact cancellation of the first order Doppler shift which opens the way for an application to a sample composed of many ions. The transfer efficiency and its dependence with experimental parameters are analyzed by numerical simulations. This efficiency is shown to reach a fidelity as high as $(1-8.10^{-5})$ with realistic parameters. The scheme is also extended to the synthesis of a linear combination of three stable or metastable states.Comment: Journal of Physics B: Atomic, Molecular and Optical Physics (2013) a paraitr

Microwave ion clock : analysis and transport of an ion cloud in a trap with several zones

Cette thèse a été effectuée dans le cadre d'un projet qui vise à explorer les facteurs limitants des performances d'une horloge à ions dans le domaine des fréquences micro-onde. Ce travail repose sur l'observation et la manipulation d'un grand nuage d'ions dans des potentiels de géométries différentes. Le but est l'analyse et le transport d'un grand nuage pouvant dépasser 10^6 ions dans un piège radio-fréquence linéaire à plusieurs zones. Notre groupe à construit un piège à trois zones destiné au piégeage d'ions calcium: deux parties quadrupolaires et une partie octupolaire montées en ligne. Les ions sont créés dans la première partie quadrupolaire et refroidis par laser le long de l'axe du piège. Nous avons d'abord étudié la création d'un grand nuage. La limite actuelle des paramètres du système permet de confiner et détecter des nuages de taille maximale 1,2.10^5 ions. Ensuite, grâce à un protocole de transport rapide et optimisé, ces ions sont transportés dans le deuxième et troisième piège avec une efficacité pouvant atteindre 100%. Les résultats en fonction de la durée de transport montrent une asymétrie entre les deux sens de transport que nous exploitons pour ajouter des ions dans le deuxième piège sans perte du nuage initialement présent. Cette technique d'accumulation a permis de piégér 2,5.10^5 ions dans le deuxième et troisième piège. Ce nombre semble limité par les refroidissement. Enfin, dans l'octupole, les observations montrent que, contrairement aux structures creuses attendues par les modèles, les ions froids s'organisent dans trois minima locaux de potentiels. La cause de cette différence est un petit défaut dans la symétrie octupolaire des barreaux.This thesis is part of a project aiming to explore the performance limiting factors of a microwave ion clock. This work is based on the observation and manipulation of a large ion cloud in potentials with different geometries. The purpose is to analyze and transport a large cloud of more than 10^6 ions in a linear radio-frequency trap with several zones. Our group has build a three-zone trap for calcium ion trapping: two quadrupole parts and an octupole part mounted inline. Ions are created in the first quadrupole part and cooled by lasers along the trap symmetry axis. We study the creation of a large ion cloud. The current trapping and cooling parameters limit the maximum size of the cloud to 1,2.10^5 ions. with a rapid and optimized transport protocol, these ions are transfered in the second part of the trap and then in the octupole trap with an efficiency of up to 100%. The result as function of the transport duration shows an asymmetry between the two transport directions. We exploit this feature to add ions in the second or third trap without loss of the already trapped ions. This accumulation technique has allowed to trap 2,5.10^5 ions in the second and third trap. The cooling laser power seems to be the major limiting factor of this number. Finally the observation of the ions in the octupole shows that the cold ions are localised in three different potential wells. This is in contradiction with the hollow structure predicted by the analytical fluid model and molecular dynamics simulations. The cause of this difference is a tiny defect in the octupole symmetry of the RF-electrodes which leads to local minima in the multipole potential