Radio-frequency Ion Trap Research Articles

Algorithmic Ground-State Cooling of Weakly Coupled Oscillators Using Quantum Logic

Most ions lack the fast, cycling transitions that are necessary for direct laser cooling. In most cases, they can still be cooled sympathetically through their Coulomb interaction with a second, coolable ion species confined in the same potential. If the charge-to-mass ratios of the two ion types are too mismatched, the cooling of certain motional degrees of freedom becomes difficult. This limits both the achievable fidelity of quantum gates and the spectroscopic accuracy. Here we introduce a novel algorithmic cooling protocol for transferring phonons from poorly- to efficiently-cooled modes. We demonstrate it experimentally by simultaneously bringing two motional modes of a Be$^{+}$-Ar$^{13+}$ mixed Coulomb crystal close to their zero-point energies, despite the weak coupling between the ions. We reach the lowest temperature reported for a highly charged ion, with a residual temperature of only $T\lesssim200~\mathrm{\mu K}$ in each of the two modes, corresponding to a residual mean motional phonon number of $\langle n \rangle \lesssim 0.4$. Combined with the lowest observed electric field noise in a radiofrequency ion trap, these values enable an optical clock based on a highly charged ion with fractional systematic uncertainty below the $10^{-18}$ level. Our scheme is also applicable to (anti-)protons, molecular ions, macroscopic charged particles, and other highly charged ion species, enabling reliable preparation of their motional quantum ground states in traps.

Reaction of carbon dication C2+ with O2 , N2 , CO, and HD at low temperatures: Experimental study using a 22-pole ion trap

We present experimental studies of reactions of doubly charged carbon cation (carbon dication, ${\mathrm{C}}^{2+}$, C iii) with ${\mathrm{O}}_{2}$, ${\mathrm{N}}_{2}$, CO, and HD molecules. A temperature-variable cryogenic linear 22-pole radio frequency ion trap was employed to obtain reaction rate coefficients and their temperature dependencies in the range from 40 to 300 K. The measured coefficients are almost independent of the temperature at the covered range. At 60 K the reaction rate coefficients are $1.4(3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{3}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ for ${\mathrm{O}}_{2}$, $1.9(4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{3}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ for ${\mathrm{N}}_{2}$, $8(2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{3}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ for CO, and $1.5(5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{3}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ for HD.

Manipulating phonons of a trapped-ion system using optical tweezers

We propose an experimental architecture where an array of optical tweezers affords site-dependent control over the confining potential of a conventional radio-frequency ion trap. The site-dependent control enables programmable manipulation of phonon modes of ions, with many potential applications in quantum information processing (QIP) and thermodynamics. We describe protocols for programming the array of optical tweezers to attain a set of target phonon modes with high accuracy. We propose applications of such controls in simulating quantum thermodynamics of a particle of programmable effective mass via Jarzynski's equality and improving the efficiency of sympathetic cooling and quantum logic gates in a multispecies ion system of disparate masses. We discuss the required optical parameters in a realistic ion trap system and potential adverse effects of optical tweezers in QIP. Our scheme extends the utility of trapped ions as a platform for quantum computation and simulation.

An ultralow-noise superconducting radio-frequency ion trap for frequency metrology with highly charged ions.

We present a novel ultrastable superconducting radio-frequency (RF) ion trap realized as a combination of an RF cavity and a linear Paul trap. Its RF quadrupole mode at 34.52MHz reaches a quality factor of Q ≈ 2.3 × 105 at a temperature of 4.1K and is used to radially confine ions in an ultralow-noise pseudopotential. This concept is expected to strongly suppress motional heating rates and related frequency shifts that limit the ultimate accuracy achieved in advanced ion traps for frequency metrology. Running with its low-vibration cryogenic cooling system, electron-beam ion trap, and deceleration beamline supplying highly charged ions (HCIs), the superconducting trap offers ideal conditions for optical frequency metrology with ionic species. We report its proof-of-principle operation as a quadrupole-mass filter with HCIs and trapping of Doppler-cooled 9Be+ Coulomb crystals.

Theoretical fractional formulation of a three-dimensional radio frequency ion trap (Paul-trap) for optimum mass separation

We investigate the dynamics of an ion confined in a Paul–trap supplied by a fractional periodic impulsional potential. The Cantor–type cylindrical coordinate method is a powerful tool to convert differential equations on Cantor sets from cantorian–coordinate systems to Cantor–type cylindrical coordinate systems. By applying this method to the classical Laplace equation, a fractional Laplace equation in the Cantor–type cylindrical coordinate is obtained. The fractional Laplace equation is solved in the Cantor–type cylindrical coordinate, then the ions is modelled and studied for confined ions inside a Paul–trap characterized by a fractional potential. In addition, the effect of the fractional parameter on the stability regions, ion trajectories, phase space, maximum trapping voltage, spacing between two signals and fractional resolution is investigated and discussed.

Multiple helium tagging and OH vibrational spectroscopy of cold protonated glycine ions

Using a wire-based cryogenic radiofrequency ion trap we have studied helium tagging of protonated glycine ions, GlyH+, at low temperatures. Time-of-flight mass spectrometry of the trapped ions shows tagging with up to four helium atoms at trap temperatures down to 3 K. From temperature-dependent ion intensities an activation energy for collision-induced dissociation is derived. A pulsed infrared laser has been used to study the OH stretching vibration by vibrational predissociation spectroscopy in trapped GlyH+(He)n (n=1 to 3), and only small shifts of the center frequency have been observed. The width of the absorption peak is explained by the simulated rotational contour of the absorption band of the trapped ions with about 6 K rotational temperature. Quantum chemical calculations of the structures of the GlyH+(He)n (n=0 to 3), the different helium binding energies, and the frequency shifts of the OH stretching vibration have been performed and found to explain the observed features qualitatively.

Experimental Study on CH+ Formation from Doubly Charged Carbon and Molecular Hydrogen

Abstract We studied the reaction of doubly charged carbon C2+ (C iii) with molecular hydrogen, a possible source of the high, unexplained abundances of interstellar CH+. The experiment was carried out using the cryogenic linear 22-pole radio frequency ion trap. The measured reaction rate coefficient amounts to (1.5 ± 0.2) × 10−10 cm3 s−1, nearly independently of the covered temperature range from 15 to 300 K. In the product distribution study, the C+ ion was identified as the dominant product of the reaction. For the CH+ production, we determine an upper limit for the reaction rate coefficient at 2 × 10−12 cm3 s−1.

The reaction of O+(4S) ions with H2, HD, and D2 at low temperatures: Experimental study of the isotope effect.

The reactions of the O+ ions in the 4S electronic ground state with D2 and HD were studied in a cryogenic 22-pole radio-frequency ion trap in the temperature range of 15 K-300 K. The obtained reaction rate coefficients for both reactions are, considering the experimental errors, nearly independent of temperature and close to the values of the corresponding Langevin collisional reaction rate coefficients. The obtained branching ratios for the production of OH+ and OD+ in the reaction of O+(4S) with HD do not change significantly with temperature and are consistent with the results obtained at higher collisional energies by other groups. Particular attention was given to ensure that the O+ ions in the trap are in the ground electronic state.

Study on the high-efficiency sympathetic cooling of mixed ion system with a large mass-to-charge ratio difference in a dual radio-frequency field by numerical simulations

This study proposes a method to achieve stable confinement and efficient sympathetic cooling of a mixed ion system in dual radiofrequency (RF) traps by numerical simulations. The dynamic coupling behavior, sympathetic cooling mechanism, and efficiency-affecting factors of the dual RF ion trap system were quantitatively analyzed by molecular dynamics simulations, yielding the stable confinement conditions of three-dimensional (3D) cold ion system in dual RF confinement fields and the characteristics of 3D correlation coupling between intrinsic micromotion and secular motion. The transient processes of ion intrinsic micromotion were also investigated. Herein, a reasonable second trapping potential contributed to the efficient cooling of the ion system and suppression of its micromotion. The effects of the dual RF trapping field strength on the spatial configuration and the dynamic coupling process of sympathetic cooling were investigated in mixed 3D ion crystals with a large mass-to-charge ratio (M/Q) difference, which reveals that simultaneous stable trapping and matching dynamic modes are the key to achieving efficient sympathetic cooling in the two-component ion system. These results are applicable to studies such as quantum logic manipulation, antimatter synthesis, dark ion detection, regulation of ultracold chemical reaction processes, and precision spectral measurements based on sympathetic cooling.

Optical Atomic Clocks for Redefining SI Units of Time and Frequency

Nowadays, most of the standards of measurement are based on fundamental constants, and among all, the SI units of time and frequency are realized with the highest precision. The SI unit of time interval, i.e. second, is realized on the basis of a hyperfine transition of ground state of 133Cesium atom in the microwave region. Atomic clocks operating at the optical frequencies have potential of providing better accuracy and higher stability than the microwave atomic clocks, and it is expected that SI second will be redefined on the basis of an optical transition. In this article, we focus on different atomic frequency standards operating in the optical domain of the spectrum by interrogating neutral atoms in optical lattice or a single ion within a radiofrequency ion trap. Recent worldwide developments along with activities at CSIR-National Physical Laboratory (CSIR-NPL) towards building optical atomic clock or optical frequency standard have also been presented.

Application of a self-injection locked cyan laser for Barium ion cooling and spectroscopy

Compact, high power lasers with narrow linewidth are important tools for the manipulation of quantum systems. We demonstrate a compact, self-injection locked, Fabry-Perot semiconductor laser diode with high output power at 493 nm. A high quality factor magnesium fluoride whispering gallery mode resonator enables both high passive stability and 1 kHz instantaneous linewidth. We use this laser for laser-cooling, in-situ isotope purifcation, and probing barium atomic ions confined in a radio-frequency ion trap. The results here demonstrate the suitability of these lasers in trapped ion quantum information processing and for probing weak coherent optical transitions.

Spatial Confinement of Microobjects in the Radiofrequency Ion Trap in a Viscous Medium

Spatial Confinement of Microobjects in the Radiofrequency Ion Trap in a Viscous Medium

Vibrational overtone spectroscopy of cold trapped hydroxyl anions

The second vibrational overtone transition, ${\ensuremath{\nu}}^{\ensuremath{'}},{J}^{\ensuremath{'}}=3,1\ensuremath{\leftarrow}\ensuremath{\nu},J=0,0$, in ${\text{OH}}^{\ensuremath{-}}$ confined in a 22-pole radio frequency ion trap has been measured using a laser induced reaction with molecular hydrogen. The resultant spectral line is found at 10 150.94(2) ${\mathrm{cm}}^{\ensuremath{-}1}$ and the excitation rate of this overtone excitation is obtained, which sensitively probes the molecular potential surface. The Doppler broadened line profile is used to determine the translational temperature of the ions in buffer gas temperatures ranging from 9(1) to 52(1) K. The translational temperatures closely follow those of the buffer gas over this range, including an offset caused by radio frequency heating. In comparison with previous measurements of the rotational temperatures of trapped ions, we show that translational and rotational temperatures do not equilibrate at the low buffer gas temperatures.

Geometry optimisation of a transparent axisymmetric ion trap for the MORA project

In the frame of the project MORA (Matter's Origin from the Radio Activity of trapped and oriented ions), a transparent axially symmetric radio-frequency ion trap (MORATrap) was designed in order to measure the triple correlation parameter $D$ in nuclear $\beta-$decay of laser-polarised ions. The trap design was inspired from the LPCTrap geometry, operated at GANIL from 2005 to 2013. In a real (non-ideal) Paul trap, the quadrupole electric potential is not perfect leading to instabilities in ion motion and therefore affecting the overall trapping efficiency. This paper presents a numerical method aiming to optimise the geometry of a trap. It is applied to MORATrap in order to improve the trapping efficiency and to enlarge the axial transparent solid angle compared to LPCTrap. In the whole optimisation process, numerical computation of electric potential and field was carried out using an electrostatic solver based on boundary element method (BEM). The optimisation consisted in minimising an objective function (fitness function) depending on higher order multipoles of the potential. Finally, systematic changes of trap dimensions and electrode displacements were applied to investigate geometrical effects on the potential quality.

X-Ray Absorption Spectrum of the N_{2}^{+} Molecular Ion.

The x-ray absorption spectrum of N_{2}^{+} in the K-edge region has been measured by irradiation of ions stored in a cryogenic radio frequency ion trap with synchrotron radiation. We interpret the experimental results with the help of restricted active space multiconfiguration theory. Spectroscopic constants of the 1σ_{u}^{-1} ^{2}Σ_{u}^{+} state, and the two 1σ_{u}^{-1}3σ_{g}^{-1}1π_{g} ^{2}Π_{u} states are determined from the measurements. The charge of the ground state together with spin coupling involving several open shells give rise to double excitations and configuration mixing, and a complete breakdown of the orbital picture for higher lying core-excited states.

Spatial Confinement of Microobjects in the Radiofrequency Ion Trap in a Viscous Medium-=SUP=-*-=/SUP=-

In the present article a spatial confinement of microobjects were explored in the radiofrequency Paul trap at normal pressure. Spores of Lycopodium Clavatum, 33 μm in diameter, and CdSe/ZnS (core/shell) quantum dots conglomerates with size of 2-7 μm were used as such microobjects. Zero-crossing orbits of these objects were observed for the first time what indicates the nonlinear nature of dynamics of these particles in localization area. Mathematical descriptions of particle dynamics in a viscous is presented. It is shown that friction value depends on the radius of microobjects and dynamic viscosity. Moreover, zero-crossing orbits of charged particles in the radiofrequency Paul trap were numerically simulated. A new method of comparative analysis of the morphology of microparticles is proposed. Keywords: ion traps, non-linear dynamic, mass-spectrometry, biological objects.

The reaction of isotope-substituted hydrated iodide I(HO)- with ozone: the reactive influence of the solvent water molecule.

We report an investigation of the reaction of isotope-substituted hydrated iodide I(HO)- with ozone 16O3 to examine the involvement of the water molecules in the oxidation reactions that terminate with the formation of IO3-. Experimentally, we studied the reaction in the gas phase as elementary reactions using a radio-frequency (RF) ion-trap combined with a quadrupole mass spectrometer (QMS). In approximately 1.2% of the reactions of I(HO)- and 16O3, the 18O atom is found to appear in iodine oxide anions, thus giving evidence for a close involvement of the water molecule in a non-negligible number of the reactions towards IO3-. As a part of the experimental investigation, the reaction rate constant for the exchange reaction I(HO)- + HO → I(HO)- + HO at 300 K was found to be (1.3 ± 0.1) × 10-8 cm3 s-1. Quantum chemical calculations are exploited to establish the energetic difference between I(HO)- and I(HO)-.

Development of a cryogenic ion mobility spectrometer for an isomer-selected photoexcitation and reaction studies

SynopsisA new development aiming experimental studies of isomer-selected gas-phase reactions and photoexcitation processes is being conducted. The experiment is based on isomer separation by an ion mobility spectrometry and ion accumulation in a temperature-variable radiofrequency ion trap. The laser plasma light source at Rikkyo University is currently under an upgrade for providing ultraviolet light at the wavelength region from 90 to 200 nm. We report on the details of the experimental setup and current status of the development.

Reaction of dication C++ with molecular hydrogen at temperature 20 K

SynopsisThe reaction of dication C++ with H2 was studied at temperature 20 K using a linear 22-pole radiofrequency ion trap. The overall reaction rate coefficient was measured as 1.4 ± 0.3 × 10−10 cm3 s−1. The upper limit for formation of CH+ in this reaction was evaluated as 4 × 10−12 cm3 s−1.

Hole Migration in Telomere-Based Oligonucleotide Anions and G-Quadruplexes.

Vacuum ultraviolet photoionization of a gas‐phase oligonucleotide anion leads to the formation of a valence hole. This hole migrates towards an energetically favorable site where it can weaken bonds and ultimately lead to bond cleavage. We have studied Vacuum UV photoionization of deprotonated oligonucleotides containing the human telomere sequence dTTAGGG and G‐quadruplex structures consisting of four dTGGGGT single strands, stabilized by NH4 + counter ions. The oligonucleotide and G‐quadruplex anions were confined in a radiofrequency ion trap, interfaced with a synchrotron beamline and the photofragmentation was studied using time‐of‐flight mass spectrometry. Oligonucleotide 12‐mers containing the 5'‐TTAGGG sequence were found to predominantly break in the GGG region, whereas no selective bond cleavage region was observed for the reversed 5'‐GGGATT sequence. For G‐quadruplex structures, fragmentation was quenched and mostly non‐dissociative single and double electron removal was observed.