Search

The radiofrequency quadrupole linear ion trap is a widely used device in physics and chemistry. When used for trapping of large ion clouds, the presence of anharmonic terms in the radiofrequency potential limits the total number of stored ions. In this paper, we have studied the anharmonic content of the trapping potential for different implementations of a quadrupole trap, searching for the geometry best suited for the trapping of large ion clouds. This is done by calculating the potential of a real trap using SIMION8.0, followed by a fit, which allows us to obtain the evolution of anharmonic terms for a large part of the inner volume of the trap., Accepted for publication at International Journal of Mass Spectrometry

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 an 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 $80\phantom{\rule{0.16em}{0ex}}000$ ions over a distance of 20 mm inside a linear radio-frequency trap. Ion transport is controlled by a transfer function, which is designed taking into account the local electric potentials. We observe that the ion response is very sensitive to the details of the description of the electric potential. Nevertheless, we show that fast transport---with a total duration of 100 $\ensuremath{\mu}s$---results in transport efficiencies attaining values higher than 90% of the ion number, even with large ion clouds. For clouds smaller than 2000 ions, a 100% transfer efficiency is observed. Transport induced heating, which depends on the transport duration, is also analyzed.

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 paraitre

An optical frequency/wavelength standard using the high line Q/sup 2/S/sub 1/2/-/sup 2/D/sub 5/2/ transition of Ca/sup +/ confined in a RF trap and laser cooled is discussed according to the following points: optical excitation scheme to cool the ions and probe the clock transition of an odd isotope of Ca/sup +/ and feasibility of the production of the optical excitations from laser diodes. >

International audience; A ring crystal of ions trapped in a linear multipole trap is studied as a basis for an optical frequency standard. The equilibrium conditions and cooling possibilities are discussed through an analytical model and molecular dynamics simulations. A configuration which reduces the frequency sensitivity to the fluctuations of the number of trapped ions is proposed. The systematic shifts for the electric quadrupole transition of calcium ions are evaluated for this ring configuration. This study shows that a ring of 10 or 20 ions allows to reach a short term stability better than for a single ion without introducing limiting long term fluctuations.

The electric quadrupole transition between the ground state and the first metastable state of a single Ca ion is an attractive choice for a frequency standard in the optical domain. Probing of the clock transition is carried out using quantum jump statistics which requires cycle times of several seconds. The spectral linewidth of the probe laser (local oscillator) must reach the hertz level for a duration at least as long as these cycle times. To reduce the TiSa laser linewidth at 729 nm, we use a KD*P electro-optic modulator (EOM) inside the laser cavity. This device shows a couple of mechanical resonances induced by piezo-electric ringing at frequencies larger than 50 kHz, limiting notably the use of the device for frequency corrections. Actual performances (Deltav < 1 kHz for tau < 1 ms) of our laser set-up allow the observation of a preliminary spectrum with Zeeman splitting of the 729 nm transition of a single trapped Ca+ ion.

Among the ions proposed for a frequency standard in the optical domain, Ca/sup +/ is one of the most favorable candidates due to its wavelengths accessible with all-solid-state laser systems. This allows to imagine an ultimate experimental setup being simple and compact. The 4S/sub 1/2/-3D/sub 5/2/ electric quadrupole transition at 729 nm with a natural linewidth below 1 Hz serves as clock transition, while laser cooling on one of the resonance lines is carried out at 397 nm. To obtain the small spectral linewidths necessary for a frequency standard performance, it is essential to reduce the residual Doppler broadening caused by the RF heating in the Paul trap. The first-order Doppler broadening of a single ion can be eliminated in the Lamb-Dicke regime where the ion's amplitude of motion is inferior to the emitted wavelength. The main condition for the access of this frequency modulation regime is a high motional frequency of the trapped ion. This is more easily obtained in a low capacitance device and thus traps with reduced dimensions are required. We have set up a miniature ion trap of the Paul-Straubel-type. The stored ions are observed by a photomultiplier in the photon-counting mode as well as by an intensified CCD camera, permitting the visualization of their spatial behavior. Laser cooling of the Ca/sup +/ ions is carried out on the 4S/sub 1/2/-4P/sup 1/2/ resonance line at 397 nm. Progress on the characterization of the trapped single ion as well as on the generation of the involved wavelengths exclusively by solid-state lasers is reported.

Publisher Summary This chapter discusses two-photon transition between the fundamental state 5d106s2S1/2 and the metastable state 5d96s22S5/2 in mercury ions confined in a radiofrequency trap. The lifetime of the metastable state is about 0,1s, and so this transition is attractive as an optical frequency standard. The chapter describes the energetic properties of the confined particles. It illustrates the calculated profile of the line, broadened and red shifted by second order Doppler effect, for different temperatures of the ions in the trap with a monochromatic laser. The chapter further illustrates width at half maximum of the observed signal in function of the temperature of the ions for different linewidths of the laser.

The purpose of our experiment is to observe the two-photon transition between the fundamental state 5d106s2S1/2 and the metastable state 5d96s22D5/2 in stored Hg+. This transition is attractive as an optical frequency standard for two reasons. First, the radiative lifetime of the 2D5/2 state is about 0.1s and second, the first-order Doppler effect cancels for a two-photon absorption. Thus the transition line consists of a very narrow carrier and we can study the second-order Doppler effect (red shift and broadening, which is estimated to be a few kHz).

Very long, one-dimensional (1D) ion chains are the basis for many applications, in particular in quantum information processing and reliable diagnostics are needed to quantify them. To that purpose, we have experimentally validated Dubin's model for very long ion chains [Phys. Rev. Lett. 71, 2753 (1993)]. This diagnostic allows to precisely determine the number of trapped ion with an accuracy of almost 1% without counting them, by measuring the ion-ion distance of the innermost particles, as well as the trapping potential along the ion chain direction. In our experiment, based on a 155 ion chain, the central 30 ions are measured to be equidistant to better than 2%, and we can determine the total number of trapped ions with a 4.5% uncertainty, completely dominated by a conservative estimation of the experimental characterisation of the trap.