Anharmonic oscillation of ions trapped in a rf trap with light buffer gas

The effect of a light buffer gas on the anharmonic oscillation of ions trapped in a rf trap is studied. The rf resonance absorption signals showed a change of the signal height and the hysteresis with the sweep direction of the dc voltage or the probing frequency due to the anharmonicity of the pseudopotential well of a rf trap. It was found that the signals changed drastically or even disappeared depending on the pressure of buffer gas, although almost the same number of ions were trapped. These effects indicate that the sensitivity of detection of the trapped ions can be improved by appropriately choosing the pressure of the buffer gas and the sweep direction. The trapped ions could be detected until 76 h 20 min and the storage time of 1.3×10⁵ s was determined when these parameters were optimized.     

Detection of parametric resonance of trapped ions for micromotion compensation

We have detected excess micromotion of trapped ions by modulating the trapping voltage. This radio-frequency (rf) modulation induces parametric resonance and excites secular motion of the trapped ions when they possess excess motion. This technique has been applied to laser-cooled ions in a linear rf trap and it provides optimum values for compensating the trapping field. We found that the technique has sensitivity equal to or greater than the conventional method for detecting excess micromotion. Because any laser propagation direction can be used, this method is expected to be applied to surface-electrode traps.     

联合阱中稳定囚禁离子的实验研究

实验观察到了小型联合阱稳定囚禁离子的射频信号增强现象，并以此对联合阱囚禁离子的特性进行了讨论；同时，通过实验检测到的稳定囚禁离子的工作点范围与磁场强度的关系，在一定程度上验证了联合阱囚禁离子稳定区随磁场强度的变化趋势。     

Three-Dimensional Compensation for Minimizing Heating of the Ion in Surface-Electrode Trap

The trapped ions confined in a surface-electrode trap(SET) could be free from rf heating if they stay at the rf potential null of the potential well.We report our effort to compensate three-dimensionally for the micromotion of a single ~(40)Ca~+ ion near the rf potential null,which largely suppresses the ion's heating and thus helps to achieve the cooling of the ion down to 3.4 mK,which is very close to the Doppler limit.This is the prerequosite of the sideband cooling in our SET.     

Generation of a decoherence-free entangled state using a radio-frequency dressed state

We propose the generation of entangled states with trapped calcium ions using a combination of an rf dressed state and a spin-dependent force. By using this method, a decoherence-free entangled state of rf qubits can be directly generated, and ideally its fidelity is close to unity. We demonstrate an rf entangled state with a fidelity of 0.68±0.08, which has a coherence time of more than 200 ms by virtue of the fact that it is an eigenstate with energy gaps between adjacent levels. Using the same technique, we also produce a qutrit-qutrit entangled state with a fidelity of 0.77±0.09, which exceeds the threshold value for separability of 2/3.     

Detection of Isotopes of Mercury Ions by Resonant Ejection in Paul Trap

A simple method to detect mercury ions confined in a Paul trap has been developed by resonant ejection. In this method, frequency of the additional ejection ac voltage is scanned instead of the amplitude of the rf drive voltage in conventional methods. It is possible not only to observe the spectra of the secular oscillation of the trapped ions directly, but also to eject the confined ions from the trap mass-selectively.     

Scaling and suppression of anomalous heating in ion traps

We measure and characterize anomalous motional heating of an atomic ion confined in the lowest quantum levels of a novel rf ion trap that features moveable electrodes. The scaling of heating with electrode proximity is measured, and when the electrodes are cooled from 300 to 150 K, the heating rate is suppressed by an order of magnitude. This provides direct evidence that anomalous motional heating of trapped ions stems from microscopic noisy potentials on the electrodes that are thermally driven. These observations are relevant to decoherence in quantum information processing schemes based on trapped ions and perhaps other charge-based quantum systems.     

Planar ion chip design for scalable quantum information processing

We investigate a planar ion chip design with a two-dimensional array of linear ion traps for scalable quantum information processing. Qubits are formed from the internal electronic states of trapped ^40Ca^＋ ions. The segmented electrodes reside in a single plane on a substrate and a grounded metal plate separately, a combination of appropriate rf and DC potentials is applied to them for stable ion confinement. Every two adjacent electrodes can generate a linear ion trap in and between the electrodes above the chip at a distance dependent on the geometrical scale and other considerations. The potential distributions are calculated by using a static electric field qualitatively. This architecture provides a conceptually simple avenue to achieving the microfabrication and large-scale quantum computation based on the arrays of trapped ions.     

Observation of laser-cooled Be+ -ion clouds in a Penning trap

Be⁺ ions trapped in a Penning trap are laser-cooled to about 10 mK. The excitation spectra of ion clouds containing about 500 ions are obtained by scanning the frequency of the cooling laser and discontinuities in these spectra are observed because of phase transitions. When the cooled ions are heated electrically by applying an rf voltage, no phase transition occurs and the spectra become continuous. Two-dimensional measurement of the ion clouds is carried out and the abrupt change in the shape of the ion cloud due to the phase transition is observed. When many ions are trapped and cooled, the phase transition occurs partially and a transient state where two states are mixed can be observed. The static properties of the ions are also measured by using an additional probe laser and the results of experimental measurements are compared with theoretical predictions.     

Optical detection of Yb+ trapped in an rf trap

The fluorescence from Yb⁺ ions trapped in an rf trap was detected by driving the²S_1/2−²P_1/2 transition at 369.52 nm with the radiation generated by sum-frequency mixing of diode-laser and argon-ion-laser radiation. The rf resonance absorption signal as well as the fluorescence signal, when the Yb⁺ ions were continuously irradiated by the resonant uv radiation, faded out with a decay time shorter than the storage time. This observation suggests that the Yb⁺ ions disappeared from the trap with the irradiation of the resonant uv radiation.     

Observation of a saturation dip in the fluorescence light from electrodynamically trapped Ba+ ions

Ba⁺ ions are trapped in a Paul rf quadrupole trap and irradiated by D1 resonance light at 493.4 nm from a tunable laser. At ion densities of about 10⁵ cm^-3 a saturation lamp dip was easily observed when two laser beams of opposite directions were used. This should allow Doppler-free optical spectroscopy on a small number of ions in the future.     

Kinetic Energy of Trapped Ions Cooled by Buffer Gas

The average kinetic energy of 40 Ca＋ ions is measured by the method of evaporating ions in an rf ion trap. The kinetic energy of the ion 40Ca＋ varies from 0.5eV to 0.2eV with changing buffer gas pressure from 10^-7 mbar to 10^-5 mbar. The Brownian motion model is also introduced to calculate the average kinetic energy of the trapped ions.     

Fluorescence Detection and Buffer Gas Cooling of Trapped Mercury Ions in Paul Trap

Pig ions are confined in a hyperboloid ion trap. With the rf discharge ^202 Hg isotope lamp, the fluorescence signal of trapped Hg ions is observed. By means of buffer gas cooling, the ionic temperature is reduced. As a result, the trapping time is increased and the signal-to-noise ratio （SNR） of the fluorescent signal is improved. The temperature of ion cloud is estimated by measuring the space charge shift.     

All-diode-laser cooling of single Ca+ ions

+ ions. The Ca⁺ ions are trapped in a miniature rf Paul trap and irradiated by light from a frequency-doubled diode laser at 397 nm and by light from a diode laser at 866 nm. We are able to cool a single ion and observe its fluorescence continuously with the laser diode locked to the external frequency-doubling cavity. Quantum jumps in the fluorescence light of a single ion and of a small cloud of five ions have been induced by driving the “clock” transition at 729 nm. We were able to resolve the influence of the micromotion on the excitation spectrum of the small ion cloud. Received: 10 July 1997/Revised version: 17 November 1997     

A compact Penning trap for light ions

We describe the construction of a novel compact Penning trap from strong permanent magnets for trapping light ions. Our cylindrically symmetric, iron-free magnetic configuration allows fully analytical treatment, is easy to handle and to optimize. The magnetic field inhomogeneity is less than 1% in a volume of 1 cm³ at 0.7 T. The stored H⁺ and H ₂ ⁺ ions in this trap are detected electrically by the rf absorption method. The charge density, total number and storage time of the trapped ions are measured.Dedicated to H. Walther on the occasion of his 60th birthday     

On the sensitivity of ion traps for spectroscopic applications

Ba⁺ ions, created by surface ionization near one endcap of an rf quadrupole trap were slowed down by collisions with the background gas. At He pressures of 10^?6 mbar or more 2% of the primary ions could be trapped. The sensitivity of ion detection by fluorescence radiation allows spectroscopic experiments, starting from less than 10⁷ particles. The observation of the ground-state hyperfine splitting of¹³⁷Ba⁺ is given as an example.     

Laser spectroscopy of trapped 7Be and 10Be at a prototype slow RI-beam facility of RIKEN

A next-generation slow radioactive nuclear ion beam facility (SLOWRI) which provides slow, high-purity and small emittance ion beams of all elements is being build as one of the principal facilities at the RIKEN RI-beam factory (RIBF). High energy radioactive ion beams from the projectile fragment separator BigRIPS are thermalized in a large gas catcher cell. The thermalized ions in the gas cell are guided and extracted to a vacuum environment by a combination of dc electric fields and inhomogeneous rf fields (rf carpet ion guide). From there the slow ion beam is delivered via a mass separator and a switchyard to various devices: such as an ion trap, a collinear fast beam apparatus, and a multi-reflection time of flight mass spectrometer. In the R&D works at the present RIKEN facility, an overall efficiency of 5% for a 100A MeV ⁸Li ion beam from the present projectile fragment separator RIPS was achieved and the dependence of the efficiency on the ion beam intensity was investigated. Recently our first spectroscopy experiment at the prototype SLOWI was performed on Be isotopes. Energetic ions of ¹⁰Be and ⁷Be from the RIPS were trapped and laser cooled in a linear rf trap and the specific mass shifts of these isotopes were measured for the first time.     

Status of the SHIPTRAP Project: A Capture and Storage Facility for Heavy Radionuclides fromSHIP

The ion trap facility SHIPTRAP is being set up to deliver very clean and cool beams of singly-charged recoil ions produced at the SHIP velocity filter at GSI Darmstadt. SHIPTRAP consists of a gas cell for stopping and thermalizing high-energy recoil ions from SHIP, an rf ion guide for extraction of the ions from the gas cell, a linear rf trap for accumulation and bunching of the ions, and a Penning trap for isobaric purification. The progress in testing the rf ion guide is reported. A transmission of about 93(5)% was achieved. This revised version was published online in July 2006 with corrections to the Cover Date.     

Three-Dimensional Array for 40Ca+ Ion Trapping

We present a three-dimensional scalable linear ion trap scheme for ion trapping and discuss its applications for the optical frequency standard and scalable quantum information processing with its parallel strings of trapped 40Ca＋ ions. The geometry here contains nine equal-distance parallel rods driven by rf, which form trapping potentials for radial confinement and two end ring electrodes biased at a few volts for axial confinement. Its feasibility is calculated by using the finite element analysis method.