Abstract Two-photon dissociation of BeH + ions is studied by detecting the fluorescence changes of Be + –BeH + bi-component Coulomb crystal in a linear Paul trap. BeH + ions generated by an exothermic reaction between electronically excited Be + ions and residual H 2 in the vacuum chamber are photon-dissociated with two photons scanning over the range of 201 nm to 208 nm. Our experiment provides a novel method to maintain the number of Be + ions stable in a Coulomb crystal with a middle ultraviolet band dissociation laser. This two-photon dissociation method extends the wavelength range of the dissociation laser for BeH + compared to the one-photon dissociation, and the method can be utilized to all alkaline earth atomic ions which require suppression of the reaction with residual H 2 gas in vacuum.
Abstract Two-photon dissociation of BeH + ions is studied by detecting the fluorescence changes of Be + –BeH + bi-component Coulomb crystal in a linear Paul trap. BeH + ions generated by an exothermic reaction between electronically excited Be + ions and residual H 2 in the vacuum chamber are photon-dissociated with two photons scanning over the range of 201 nm to 208 nm. Our experiment provides a novel method to maintain the number of Be + ions stable in a Coulomb crystal with a middle ultraviolet band dissociation laser. This two-photon dissociation method extends the wavelength range of the dissociation laser for BeH + compared to the one-photon dissociation, and the method can be utilized to all alkaline earth atomic ions which require suppression of the reaction with residual H 2 gas in vacuum.
The lifetime of Ba+ ions confined in a Paul trap is found, under typical conditions, to be limited by chemical reactions with residual background gas. An integrated ion-trap and time-of-flight mass spectrometer are used to analyze the reactions of the trapped Ba+ ions with three common gases in an ultrahigh vacuum system (H2, CO2, and H2O). It is found that the products of these reactions can all be photodissociated by a single ultraviolet laser at 225 nm, thereby allowing the recovery of the Ba+ ions and leading to an increase of the effective trap lifetime. For a Coulomb crystal, the lifetime increased from roughly 6 h to 2 days at room temperature. It is suggested that higher enhancement factors are possible in systems with stronger traps. In addition, photodissociation wavelengths for other common trapped-ion systems are provided.
Molecular ions that are generated by chemical reactions with trapped atomic ions can serve as an accessible testbed for developing molecular quantum technologies. On the other hand, they are also a hindrance to scaling up quantum computers based on atomic ions, as unavoidable reactions with background gases destroy the information carriers. Here, we investigate the single- and two-photon dissociation processes of single CaOH+ molecular ions co-trapped in Ca+ ion crystals using a femtosecond laser system. We report the photodissociation cross section spectra of CaOH+ for single-photon processes at λ = 245-275 nm and for two-photon processes at λ = 500-540 nm. Measurements are interpreted with quantum-chemical calculations, which predict the photodissociation threshold for CaOH+ → Ca+ + OH at 265 nm. This result can serve as a basis for dissociation-based spectroscopy for studying the internal structure of CaOH+. The result also gives a prescription for recycling Ca+ ions in large-scale trapped Ca+ quantum experiments from undesired CaOH+ ions formed in the presence of background water vapor.
We demonstrate photodissociation of BeH+ ions within a Coulomb crystal of thousands of 9Be+ ions confined in a Penning trap. Because BeH+ ions are created via exothermic reactions between trapped, laser-cooled Be+(2P3/2) and background H2 within the vacuum chamber, they represent a major contaminant species responsible for infidelities in large-scale trapped-ion quantum-information experiments. The rotational-state-insensitive dissociation scheme described here makes use of 157-nm photons to produce Be+ and H as products, thereby restoring Be+ ions without the need for reloading. This technique facilitates longer experiment runtimes at a given background H2 pressure and may be adapted for removal of MgH+ and AlH+ impurities.
Electron localization of linear symmetric molecular ion H32+
Electron localization in the dissociation of the symmetric linear molecular ion H-3(2+) is investigated. The numerical simulation shows that the electron localization distribution is dependent on the central frequency and peak electric field amplitude of the external ultrashort ultraviolet laser pulse. When the electrons of the ground state are excited onto the 2p sigma(2)Sigma(+)(u) by a one-photonprocess, most electrons of the dissociation states are localized at the protons on both sides symmetrically. Almost no electron is stabilized at the middle proton due to the odd symmetry of the wave function. With the increase of the frequency of the external ultraviolet laser pulse, the electron localization ratio of the middle proton increases, for more electrons of the ground state are excited onto the higher 3p sigma(2)Sigma(+)(u) state. 50.9% electrons of all the dissociation events can be captured by the middle Coulomb potential well through optimizing the central frequency and peak electric field amplitude of the ultraviolet laser pulse. Besides, a direct current (DC) electric field can be utilized to control the electron motions of the dissociation states after the excitation of an ultraviolet laser pulse, and 68.8% electrons of the dissociation states can be controlled into the middle proton.
In this work, the setup of an experiment aimed at high-precision laser spectroscopy of ultracold molecular hydrogen ions, started at the University of Konstanz in 1999 [1,2], was continued and first results were obtained. In particular, a new linear rf trap and a new trap supply electronics were built, the latter being capable of driving the linear rf trap with a maximum rf amplitude of > 1000V at a frequency of 14.2MHz. This made possible the simultaneous trapping of a large mass range (2u For laser cooling of Be+ ions, doubly resonant sum-frequency generation (DR-SFG) of 313nm laser light was performed between a resonantly frequency-doubled monolithic Nd:Yag laser and a Ti:sapphire laser, emitting at 532 and 760nm wavelength, respectively. An output power of P_UV > 100mW was achieved at 313nm wavelength, with a high spectral purity (rms short-term frequency fluctuations With this experimental setup, sympathetic cooling of N+, BeD+, BeH+, 4He+, HD+, and D+ ions by the laser-cooled Be+ ions was demonstrated, using laser-cooled fluorescence mass spectrometry (LCF-MS) to detect the sympathetically cooled species. Accordingly, sympathetic cooling at a minimum mass ratio of m(H2+)/m(Be+) = 0.22 was shown to be possible with both the sympathetically and laser-cooled ions in a cloud-like state. This points out the incorrectness of the theoretical lower limit m_SC/m_LC = 0.53 which was predicted in Ref.[3]. Here, the subscripts SC and LC denote the sympathetically and the laser-cooled species, respectively.
In a further experiment, almost pure Be+ ion plasmas were laser-cooled down to temperatures in the milli-Kelvin range, leading to the crystallization of the Be+ ion plasmas. The outer shapes of different-sized Be+ ion crystals in a fully anisotropic trap potential were compared with the charged fluid predictions, showing good agreement at sufficiently large numbers of Be+ ions. By fitting Voigt profiles to the measured fluorescence signal, a typical temperature T(Be+) of 30mK was estimated for the Be+ ions.
Finally, an ultracold sample of 4He+ ions [T(He+) approximately 40mK] was produced for the first time by sympathetic crystallization of the 4He+ ions. This may open up perspectives for the high-precision laser spectroscopy of 4He+ (and 3He+).
[1] T.K.W. Boley, Diplomarbeit, Universitat Konstanz (1999)
[2] H. Schnitzler, Dissertation, Universitat Konstanz (2001)
[3] T. Baba and I. Waki, Appl.Phys.B, 74, 375-382 (2002)
We present studies on monoisotopic Hg+ ions generation and trapping at room temperature. An ultraviolet laser system, including a frequency-controlled 194 nm laser and a 254 nm laser, is constructed. Mercury atoms are isotope-selectively excited by the 254 nm laser. The spectrum of the 6s2–6s6p transition lines for natural mercury isotopes is measured, and the uncertainty is less than 100 MHz. Then, the selected mercury isotopes are ionized by the 194 nm laser and trapped in a linear Paul trap. The fluorescence of the ion crystal at 194 nm is detected, and the temperature of the ions is estimated to be less than 10 mK.