All-optical ion generation for ion trap loading

We have investigated the all-optical generation of ions by photo-ionisation of atoms generated by pulsed laser ablation. A direct comparison between a resistively heated oven source and pulsed laser ablation is reported. Pulsed laser ablation with 10 ns Nd:YAG laser pulses is shown to produce large calcium flux, corresponding to atomic beams produced with oven temperatures greater than 650 K. For an equivalent atomic flux, pulsed laser ablation is shown to produce a thermal load more than one order of magnitude smaller than the oven source. The atomic beam distributions obey Maxwell–Boltzmann statistics with most probable speeds corresponding to temperatures greater than 2200 K. Below a threshold pulse fluence between 280 mJ/cm² and 330 mJ/cm², the atomic beam is composed exclusively of ground-state atoms. For higher fluences ions and excited atoms are generated.     

Laser probing of ions confined in a cylindrical radiofrequency trap

We measure the lifetime of the 5 ²D_{$\text{5}\text{2}$} metastable level of Ba⁺ ions confined in a cylindrical radiofrequency trap as well as some parameters which characterize the confining properties of the trap. This is accomplished by studying the ion response to a short pulsed optical excitation saturating the 6 ²S_{$\text{1}\text{2}$}–6 ²P_{$\text{3}\text{2}$} transition.The measured lifetime of the 5 ²D_{$\text{5}\text{2}$} metastable level is 47 ± 16 s. The storage voltages for which the ion number shows a maximum are experimentally investigated. Their change when a light buffer gas is added is observed. The effect of this gas on the storage time is also specified.     

Trapping of ions from high energy sources into a radiofrequency ion trap

An attempt is described to confine ions, created externally and accelerated to some energy, in an rf quadrupole trap. 4 keV Ba⁺ ions were stopped on a Ni foil, placed in an aperture of one trap electrode. The Ba then was evaporated from the heated foil and ionized by electron impact. At background pressure of about 10^–5 mbar of various light buffer gases (He, H₂, N₂), the trap was filled once with 10⁵ ions, at a minimum primary ion number of 10¹⁰. The storage time was 10 min. From the data obtained the possibility of spectroseopic experiments on rare isotopes, created with accelerators or nuclear reactors, is discussed.     

Isotope selective loading of an ion trap using resonance-enhanced two-photon ionization

We have demonstrated that resonance-enhanced two-photon ionization of atomic beams provides an effective tool for isotope selective loading of ions into a linear Paul trap. Using a tunable, narrow-bandwidth, continuous wave (cw) laser system for the ionization process, we have succeeded in producing Mg⁺ and Ca⁺ ions at rates controlled by the atomic beam flux, the laser intensity, and the laser frequency detuning from resonance. We have observed that with a proper choice of control parameters, it is rather easy to load a specific number of ions into a string. This observation has direct applications in quantum optics and quantum computation experiments. Furthermore, resonant photo-ionization loading facilitates the formation of large isotope-pure Coulomb crystals. Received: 21 December 1999 / Published online: 11 May 2000     

The energy distribution of an ion in a radiofrequency trap interacting with a nonuniform neutral buffer gas

An ion in a radiofrequency (rf) trap sympathetically cooled by a simultaneously trapped neutral buffer gas exhibits deviations from thermal statistics caused by collision-induced coupling of the rf field to the ion motion. For a uniform density distribution of the buffer gas, the energy distribution of the ion can be described by Tsallis statistics. Moreover, runaway heating of the ion occurs if the buffer gas particles are sufficiently heavy relative to the ion. In typical experiments, however, ultracold buffer gases are confined in traps resulting in localised, non-uniform density distributions. Using a superstatistical approach, we develop an analytical model for an ion interacting with a localised buffer gas. We demonstrate theoretically that limiting collisions to the centre of the ion trap enables cooling at far greater mass ratios than achievable using a uniform buffer gas, but that an upper limit to the usable mass ratio exists even in this case. Furthermore, we analytically derive the functional form of the energy distribution for an ion interacting with a buffer gas held in a harmonic potential. The analytical distribution obtained is found to be in excellent agreement with the results of numerical simulations.     

Quantum chaos of an ion trapped in a linear ion trap

We describe the transition to quantum chaos of an ion trapped in a linear ion trap and interacting with two laser fields. Under the conditions of adiabatic illumination of the upper level of the ion, and when the frequencies of the two laser beams are slightly different, the system is reduced to a quantum linear oscillator interacting with a monochromatic wave. The property of localization over the quantum resonance cells is proposed to exploit in order to facilitate the process of measurement of the probability distribution of an ion on the vibrational levels. In the regime of strong chaos the time-averaged values of the energy and dispersion of energy are computed and compared with the corresponding classical quantities for different values of the perturbation amplitude. In the exact resonance case, the classical analog of the system possesses an infinite inhomogeneous stochastic web. We analyze the quantum dynamics inside the inhomogeneous web. It is shown that the quantum system mimics on average the dynamics of the corresponding classical system. Formation of the quantum resonance cells is illustrated in the case of a finite detuning from the exact resonance, and under increasing of the wave amplitude. The parameters of the model and the initial conditions are close to the real physical situation which can be realized in the system of cold trapped ion perturbed by two lasers fields with close frequencies. (c) 2000 American Institute of Physics.     

Detecting vacuum entanglement in a linear ion trap

We propose and study a method for detecting ground-state entanglement in a chain of trapped ions. We show that the entanglement between single ions or groups of ions can be swapped to the internal levels of two ions by sending laser pulses that couple the internal and motional degrees of freedom. This allows us to entangle two ions without actually performing gate operations. A proof of principle of the effect can be realized with two trapped ions and is feasible with current technology.     

Temperature measurement of a single ion in a Penning trap

The present work is concerned with the association of a temperature to a single ion stored in a Penning ion trap. Several methods are described which allow to determine the temperature by measurements of the ions cyclotron and axial trapping frequencies. Recent results of a measurement on a hydrogen-like carbon ion ¹²C^{5 +} by use of mode coupling are presented and possible further applications are discussed.Received: 8 July 2004, Published online: 6 December 2004PACS: 07.20.-n. Thermal instruments and apparatus - 07.20.Dt. Thermometers - 42.50.Lc Quantum fluctuations - 42.50.Vk Mechanical effects of light on ions     

Octupolar excitation of ion motion in a penning trap

The excitation of the motion of ions in a Penning trap at twice their cyclotron frequency, 2ν _c , by means of an azimuthal octupolar RF field has been studied with the LEBIT facility at the NSCL. The possibility of such an RF octupolar excitation has been verified. Compared to ion excitation at ν _c by means of quadrupolar fields an increased resolving power is observed in the cyclotron resonance curves, which may have important implications for Penning trap mass measurements. Numerical simulations have been used to characterize important properties of this type of excitation in detail and to predict the behavior of the ion motion under realistic conditions. Good agreement with the experimental results is observed.      

Photodetachment of cold OH- in a multipole ion trap

The absolute photodetachment cross section of OH- anions at a rotational and translational temperature of 170 K is determined by measuring the detachment-induced decay rate of the anions in a multipole radio-frequency ion trap. In comparison with previous results, the obtained cross section shows the importance of the initial rotational-state distribution. Using a tomography scan of the photodetachment laser through the trapped ion cloud, the derived cross section is model-independent and thus features a small systematic uncertainty. The tomography also yields the column density of the OH- anions in the 22-pole ion trap in good agreement with the expected trapping potential of a large field free region bound by steep potential walls.     

Loading rate of Yb<Superscript>+</Superscript> loaded through photoionization in radiofrequency ion trap

We investigate the loading rate of Yb⁺ ions loaded through photoionization in a radiofrequency trap. The absolute or relative number of the loaded trapped ions is measured by use of an electric resonance of the secular motion. This method is applicable even in the presence of anharmonicity. In two-color photoionization, where the first-excitation laser drives the ¹S₀–¹P₁ transition in the Yb atom and the second one ionizes the atom from the ¹P₁ state, the loading rate is at its highest by the excitation of the ionization potential. A similar loading rate is observed at the second-laser wavelength around 369.5 nm, which is the wavelength for the cooling transition of Yb⁺. We estimate the loading cross section to be 40(15) Mb for the two-color excitation of the ionization potential. The excitation of the Yb atoms in the Rydberg states is detected by the enhancement of the loading rate. By irradiation with only the first-excitation laser, Yb⁺ is produced at a rate three orders of magnitude smaller than that when the non-resonant two-photon absorption from the ¹P₁ state is the dominant process. We also measure the charge-exchange rate between Yb⁺ and Yb, and discuss its effect on isotope-selective photoionization loading.     

Paul阱中存储离子的研究

根据Paul离子阱结构及电场分布特点,列出阱内离子运动方程并求解,对其中离子运动、硅团簇离子碰撞解离反应进行了分析.     

Penning阱中离子运动的分析

根据Penning离子阱结构及电磁场分布特点,列出阱内离子运动方程并进行求解,对其中沿z轴运动和在xy平面上的运动进行详细分析,最后得到比荷为m/q的离子在Penning阱内的运动为沿磁场方向的简谐振动、绕磁感线旋转的回旋运动和垂直于z轴及径向绕z轴的漂移运动的叠加.     

A single trapped ion in a finite range trap

This paper presents a method to describe dynamics of an ion confined in a realistic finite range trap. We model this realistic potential with a solvable one and we obtain dynamical variables (raising and lowering operators) of this potential. We consider coherent interaction of this confined ion in a finite range trap and we show that its center-of-mass motion steady state is a special kind of nonlinear coherent states. Physical properties of this state and their dependence on the finite range of potential are studied.     

Microfabricated surface ion trap on a high-finesse optical mirror

A novel approach to optics integration in ion traps is demonstrated based on a surface electrode ion trap that is microfabricated on top of a dielectric mirror. Additional optical losses due to fabrication are found to be as low as 80 ppm for light at 422 nm. The integrated mirror is used to demonstrate light collection from, and imaging of, a single Sr88(+) ion trapped 169±4 μm above the mirror.     

Continuous loading of a conservative potential trap from an atomic beam

We demonstrate the fast accumulation of 52Cr atoms in a conservative potential from a guided atomic beam. Without laser cooling on a cycling transition, a dissipative step involving optical pumping allows us to load atoms at a rate of 2×10(7) s(-1) in the trap. Within less than 100 ms we reach the collisionally dense regime, from which we produce a Bose-Einstein condensate with subsequent evaporative cooling. This constitutes a new approach to degeneracy where Bose-Einstein condensation can be reached without a closed cycling transition, provided that a slow beam of particles can be produced.