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We have successfully implemented the first simultaneous magneto-optical trapping (MOT) of lithium ($^6$Li) and ytterbium ($^{174}$Yb) atoms, towards production of ultracold polar molecules of LiYb. For this purpose, we developed the dual atomic oven which contains both atomic species as an atom source and successfully observed the spectra of the Li and Yb atoms in the atomic beams from the dual atomic oven. We constructed the vacuum chamber including the glass cell with the windows made of zinc selenium (ZnSe) for the CO$_2$ lasers, which are the useful light sources of optical trapping for evaporative and sympathetic cooling. Typical atom numbers and temperatures in the compressed MOT are 7$\times10^3$ atoms, 640 $\mu$K for $^6$Li, 7$\times10^4$ atoms and 60 $\mu$K for $^{174}$Yb, respectively., Comment: 6 pages, 4 figures

We performed evaporative cooling for dilute gases of ytterbium (Yb) isotopes in a crossed optical dipole trap and successfully cooled two fermionic and two bosonic species down to quantum degenerate regime, following the previous realization of Bose-Einstein condensation (BEC) in 174Yb. The elastic collision rate of fermionic 173Yb atoms with 6 spin components was found to be large enough to carry out efficient evaporation, which enables us to cool the atoms down to 0.6 T F , where T F is the Fermi temperature. In this regime, a plunge of evaporation efficiency was observed as an effect of the Fermi degeneracy. The other fermionic isotope 171Yb was cooled down to the temperature below T F by sympathetic cooling with bosonic 174Yb atoms. The sympathetic cooling technique has also been applied to 174Yb-176Yb Bose-Bose mixture. We have observed almost pure BEC of 174Yb and the bimodal distribution of 176Yb, showing the formation of BEC-BEC mixture. Moreover, we performed evaporative cooling of 170Yb atoms and realized the BEC.

We present the production of dual-species Bose-Einstein condensates (BECs) of $^{39}\mathrm{K}$ and $^{87}\mathrm{Rb}$. Preparation of both species in the $\left|F=1,{m}_{F}=\ensuremath{-}1\right\ensuremath{\rangle}$ state enabled us to exploit a total of three Feshbach resonances, which allows for simultaneous Feshbach tuning of the $^{39}\mathrm{K}$ intraspecies and the $^{39}\mathrm{K}\text{\ensuremath{-}}^{87}\mathrm{Rb}$ interspecies scattering length. Thus dual-species Bose-Einstein condensates were produced by sympathetic cooling of $^{39}\mathrm{K}$ with $^{87}\mathrm{Rb}$. A dark spontaneous force optical trap was used for $^{87}\mathrm{Rb}$ to reduce the losses in $^{39}\mathrm{K}$ due to light-assisted collisions in the optical trapping phase, which can be of benefit for other dual-species experiments. The tunability of the scattering length was used to perform precision spectroscopy of the interspecies Feshbach resonance located at 117.56(2) G and to determine the width of the resonance to 1.21(5) G by rethermalization measurements. The transition region from miscible to immiscible dual-species condensates was investigated and the interspecies background scattering length was determined to $28.5{a}_{0}$ using an empirical model. This paves the way for dual-species experiments with $^{39}\mathrm{K}$ and $^{87}\mathrm{Rb}$ BECs ranging from molecular physics to precision metrology.

Thermalization of a system in the presence of a heat bath has been the subject of many theoretical investigations especially in the framework of solid-state physics. In this setting, the presence of a large bandwidth for the frequency distribution of the harmonic oscillators schematizing the heat bath is crucial, as emphasized in the Caldeira-Leggett model. By contrast, ultracold gases in atomic traps oscillate at well-defined frequencies and therefore seem to lie outside the Caldeira-Leggett paradigm. We introduce interaction Hamiltonians which allow us to adapt the model to an atomic physics framework. The intrinsic nonlinearity of these models differentiates them from the original Caldeira-Leggett model and calls for a nontrivial stability analysis to determine effective ranges for the model parameters. These models allow for molecular dynamics simulations of mixtures of ultracold gases, which is of current relevance for optimizing sympathetic cooling in degenerate Bose-Fermi mixtures., 14 pages, 7 figures

We model sympathetic cooling of ground-state CaF molecules by ultracold Li and Rb atoms. The molecules are moving in a microwave trap, while the atoms are trapped magnetically. We calculate the differential elastic cross sections for CaF-Li and CaF-Rb collisions, using model Lennard-Jones potentials adjusted to give typical values for the s-wave scattering length. Together with trajectory calculations, these differential cross sections are used to simulate the cooling of the molecules, the heating of the atoms, and the loss of atoms from the trap. We show that a hard-sphere collision model based on an energy-dependent momentum transport cross section accurately predicts the molecule cooling rate but underestimates the rates of atom heating and loss. Our simulations suggest that Rb is a more effective coolant than Li for ground-state molecules, and that the cooling dynamics are less sensitive to the exact value of the s-wave scattering length when Rb is used. Using realistic experimental parameters, we find that molecules can be sympathetically cooled to 100$\mu$K in about 10s. By applying evaporative cooling to the atoms, the cooling rate can be increased and the final temperature of the molecules can be reduced to 1$\mu$K within 30s., Comment: 16 pages, 14 figures. Minor corrections picked up at proof stage

Typical sources of ultracold atoms operate with a considerable delay between the delivery of ensembles due to sequential trapping and cooling schemes. Therefore, alternative schemes for the continuous generation of ultracold atoms are highly desirable. Here, we demonstrate the continuous loading of a magnetic trap from a quasi-continuous atom beam. We achieve a steady state with $3.8 \times 10^7$ magnetically trapped atoms and a temperature of $102 \mu$K. The ensemble is protected from laser light sources, a requirement for its application for metrological tasks or sympathetic cooling. The continuous scheme is robust and applicable to a wide range of particles and trapping potentials., Comment: 5 pages, 6 figures

We investigate the dynamics of an ion sympathetically cooled by another laser-cooled ion or small ion crystal. To this end, we develop simple models of the cooling dynamics in the limit of weak Coulomb interactions. Experimentally, we create a two-ion crystal of Ca$^+$ and Al$^+$ by photo-ionization of neutral atoms produced by laser ablation. We characterize the velocity distribution of the laser-ablated atoms crossing the trap by time-resolved fluorescence spectroscopy. We observe neutral atom velocities much higher than the ones of thermally heated samples and find as a consequence long sympathethic cooling times before crystallization occurs. Our key result is a new technique for detecting the loading of an initially hot ion with energy in the eV range by monitoring the motional state of a Doppler-cooled ion already present in the trap. This technique not only detects the ion but also provides information about dynamics of the sympathetic cooling process., 23 pages, 10 figures, small corrections and extensions in response to referee comments

Molecular ions can be held in a chain of laser-cooled atomic ions by sympathetic cooling. This system is ideal for performing high-precision molecular spectroscopy with applications in astrochemistry and fundamental physics. Here we show that this same system can be coupled with a broadband laser to discover new molecular transitions. We use three-ion chains of Ca$^{+}$ and CaH$^{+}$ to observe vibrational transitions via resonance enhanced multiphoton dissociation detected by Ca$^{+}$ fluorescence. Based on theoretical calculations, we assign the observed peaks to the transition from the ground vibrational state, $\nu=0$, to $\nu=9$ and $\nu=10$. Our method allows us to track single molecular events, and it can be extended to work with any molecule by using normal mode frequency shifts to detect the dissociation. This survey spectroscopy serves as a bridge to the precision spectroscopy required for molecular ion control., Comment: 11 pages, 3 figures, updated to published version

We investigate the problem of a single ion in a radio-frequency trap and immersed in an ultracold Bose gas either in a condensed or a non-condensed phase. We develop master equation formalism describing the sympathetic cooling and we determine the cooling rates of ions. We show that cold atomic reservoir modifies the stability diagram of the ion in the Paul trap creating the regions where the ion is either cooled or heated due to the energy quanta exchanged with the time-dependent potential., Comment: 11 pages, 4 figures, extended and substantially revised version of the article

We theoretically investigate the dynamics of a trapped ion immersed in a spatially localized buffer gas. For a homogeneous buffer gas, the ion's energy distribution reaches a stable equilibrium only if the mass of the buffer gas atoms is below a critical value. This limitation can be overcome by using multipole traps in combination with a spatially confined buffer gas. Using a generalized model for elastic collisions of the ion with the buffer-gas atoms, the ion's energy distribution is numerically determined for arbitrary buffer-gas distributions and trap parameters. Three regimes characterized by the respective analytic form of the ion's equilibrium energy distribution are found. Final ion temperatures down to the millikelvin regime can be achieved by adiabatically decreasing the spatial extension of the buffer gas and the effective ion trap depth (forced sympathetic cooling).

International audience; According to the mean-field theory a condensed Bose-Bose mixture collapses when the interspecies attraction becomes stronger than the geometrical average of the intraspecies repulsions, $g_{12}^2>g_{11} g_{22}$. We show that instead of collapsing such a mixture gets into a dilute liquid-like droplet state stabilized by quantum fluctuations thus providing a direct manifestation of beyond mean-field effects. We study various properties of the droplet and find, in particular, that in a wide range of parameters its excitation spectrum lies entirely above the particle emission threshold. The droplet thus automatically evaporates itself to zero temperature, the property potentially interesting by itself and from the viewpoint of sympathetic cooling of other systems.

Preparing highly charged ions (HCIs) in a cold and strongly localized state is of particular interest for frequency metrology and tests of possible spatial and temporal variations of the fine structure constant. Our versatile preparation technique is based on the generic modular combination of a pulsed ion source with a cryogenic linear Paul trap. Both instruments are connected by a compact beamline with deceleration and precooling properties. We present its design and commissioning experiments regarding these two functionalities. A pulsed buncher tube allows for the deceleration and longitudinal phase-space compression of the ion pulses. External injection of slow HCIs, specifically Ar13+, into the linear Paul trap and their subsequent retrapping in the absence of sympathetic cooling is demonstrated. The latter proved to be a necessary prerequisite for the multi-pass stopping of HCIs in continuously laser-cooled Be+ Coulomb crystals. © 2015 AIP Publishing LLC.

We present the production of dual-species Bose-Einstein condensates of $^{39}\mathrm{K}$ and $^{87}\mathrm{Rb}$. Preparation of both species in the $\left| F=1,m_F=-1 \right\rangle$ state enabled us to exploit a total of three Fesh\-bach resonances which allows for simultaneous Feshbach tuning of the $^{39}\mathrm{K}$ intraspecies and the $^{39}\mathrm{K}$-$^{87}\mathrm{Rb}$ interspecies scattering length. Thus dual-species Bose-Einstein condensates were produced by sympathetic cooling of $^{39}\mathrm{K}$ with $^{87}\mathrm{Rb}$. A dark spontaneous force optical trap was used for $^{87}\mathrm{Rb}$, to reduce the losses in $^{39}\mathrm{K}$ due to light-assisted collisions in the optical trapping phase, which can be of benefit for other dual-species experiments. The tunability of the scattering length was used to perform precision spectroscopy of the interspecies Feshbach resonance located at $117.56(2)\,\mathrm{G}$ and to determine the width of the resonance to $1.21(5)\,\mathrm{G}$ by rethermalization measurements. The transition region from miscible to immiscible dual-species condensates was investigated and the interspecies background scattering length was determined to $28.5\,a_\mathrm{0}$ using an empirical model. This paves the way for dual-species experiments with $^{39}\mathrm{K}$ and $^{87}\mathrm{Rb}$ BECs ranging from molecular physics to precision metrology., 9 pages, 9 figures

We present a theoretical study of elastic and rotationally inelastic collisions of NH3 and ND3 with rare gas atoms (He, Ne, Ar, Kr, Xe) at low energy. Quantum close-coupling calculations have been performed for energies between 0.001 and 300 cm-1. We focus on collisions in which NH3 is initially in the upper state of the inversion doublet with j = 1, k = 1, which is the most relevant in an experimental context as it can be trapped electrostatically and Stark-decelerated. We discuss the presence of resonances in the elastic and inelastic cross sections, as well as the trends in the inelastic cross sections along the rare gas series and the differences between NH3 and ND3 as a colliding partner. We also demonstrate the importance of explicitly taking into account the umbrella (inversion) motion of NH3 in order to obtain accurate scattering cross sections at low collision energy. Finally, we investigate the possibility of sympathetic cooling of ammonia using cold or ultracold rare gas atoms. We show that some systems exhibit a large ratio of elastic to inelastic cross sections in the cold regime, which is promising for sympathetic cooling experiments. The close-coupling calculations are based on previously reported ab initio potential energy surfaces for NH3-He and NH3-Ar, as well as on new, four-dimensional, potential energy surfaces for the interaction of ammonia with Ne, Kr, and Xe, which were computed using the coupled-cluster method and large basis sets. We compare the properties of the potential energy surfaces corresponding to the interaction of ammonia with the various rare gas atoms., SCOPUS: ar.j, info:eu-repo/semantics/published

We have produced large samples of ultracold (

We propose determination of isotope shifts for radioactive beryllium isotopes using laser cooled ions in a linear radio frequency (RF) trap. Based on these measurements, combined with precise mass shift calculations, it will be possible to extract model-independent nuclear charge radii of 7,9,10Be and the one-neutron halo 11Be with precision better than 3%. Radioactive beryllium isotopes produced at ISOLDE and ionized with a laser ion source will be cooled and bunched in the radio frequency quadrupole buncher of ISOLTRAP. Ion temperatures will be reduced to the mK range by sympathetic cooling with co-trapped laser cooled ions in a specially designed two-stage linear RF trap. Resonances will be detected via fluorescence and frequencies measured with a femtosecond frequency comb.

Evaporative cooling of ultracold Yb atoms near the quantum-degenerate regime was experimentally studied. Three bosons of 170 Yb, 172 Yb, 176 Yb and two fermions of 171 Yb and 173 Yb were evaporatively cooled in a crossed far-off resonant trap (FORT). We observed that 170 Yb and 172 Yb were not concentrated into the crossed region. We found that, in the cases of 176 Yb atoms, atoms were concentrated well into the crossed region. The following evaporative cooling in the crossed region, however, did not work well. We performed the simultaneous trapping and sympathetic cooling in the crossed FORT by use of 172Yb-174Yb, 174 Yb- 176 Yb, 172 Yb- 176 Yb, and 171 Yb- 174 Yb pairs. We observed that evaporative cooling worked well. This result shows that we succeeded in the enhancement of the atom collision rate. Especially, by use of 174 Yb- 176 Yb mixture, we obtained cold 176 Yb whose phase space density was 0.02. We observed a large atom loss, which limited the further sympathetic evaporative cooling. We also evaporatively cooled 174 Yb in a ID optical lattice. Evaporative cooling worked very well because the atoms were initially trapped at a high density. After evaporative cooling, we obtained very cold atoms, and T/T F was estimated to be 1.2.

Optically trapped dielectric objects are well suited for reaching the quantum regime of their center of mass motion in an ultra-high vacuum environment. We show that ground state cooling of an optically trapped nanosphere is achievable when starting at room temperature, by sympathetic cooling of a cold atomic gas optically coupled to the nanoparticle. Unlike cavity cooling in the resolved sideband limit, this system requires only a modest cavity finesse and it allows the cooling to be turned off, permitting subsequent observation of strongly-coupled dynamics between the atoms and sphere. Nanospheres cooled to their quantum ground state could have applications in quantum information science or in precision sensing., 6 pages, 2 figures

We demonstrate sympathetic sideband cooling of a $^{40}$CaH$^{+}$ molecular ion co-trapped with a $^{40}$Ca$^{+}$ atomic ion in a linear Paul trap. Both axial modes of the two-ion chain are simultaneously cooled to near the ground state of motion. The center of mass mode is cooled to an average quanta of harmonic motion $\overline{n}_{\mathrm{COM}} = 0.13 \pm 0.03$, corresponding to a temperature of $12.47 \pm 0.03 ~\mu$K. The breathing mode is cooled to $\overline{n}_{\mathrm{BM}} = 0.05 \pm 0.02$, corresponding to a temperature of $15.36 \pm 0.01~\mu$K., Comment: 8 pages, 3 figures

A dual hybrid ion–neutral trap has been built to study collisions between a cloud of ultracold atoms and small numbers of co-trapped atomic or molecular ions, in a common volume. Ultracold Na atoms are trapped in a vapour-cell magneto-optical trap (MOT), via a single-mode frequency-stabilized ring-dye laser, with repumping. A linear rf quadrupole Paul ion trap, centred on the MOT, co-traps selected atomic or molecular ions, for example Ca+. Control of the initial ion temperature involves laser cooling Ca+ ions via the resonant Fraunhofer K line at 397 nm. We showed the rf ion trap can operate simultaneously with the MOT without destroying the ultracold atom cloud. The goal is to investigate the physics of ion–neutral sympathetic cooling, the cooling by neutrals of translationally cold and vibrorotationally hot molecular ions (e.g. Na2 +(v*, J*)), and the observation of other ion–neutral processes near 0 K, of potential interest in astrophysics.

Rare calcium isotope 48Ca+ (0.187%) has been selectively loaded in a linear Paul trap using two ultraviolet light emitting diodes with the output power of 85 mW for the second excitation in a two-step photo-ionization process. Isotope selectivity has been achieved by utilizing the isotope shifts for the 4s2 1 S 0–4s4p1 P 1 transition of neutral calcium atom. Sympathetic cooling of 48Ca+ ions has been demonstrated using 40Ca+ ions as refrigerant ions. Purification of rare isotope 42Ca+ ions (0.647%) from a mixture of 40Ca+ (96.9%) and 42Ca+ ions has been performed by adjusting the detuning of the cooling laser frequency, which overcomes the imperfect selectivity for some rare isotopes having close resonance frequencies to that of 40Ca in the 4s2 1 S 0–4s4p1 P 1 transition. The methods can be applied to 43Ca+ ion (0.135%) that has been considered as one of the attractive candidates for quantum information processing as well as for an optical frequency standard.

We have produced ensembles of cold 16O+2, 40Ar+, 12C16O+2, and various isotopes of barium ions (135Ba+, 136Ba+ and 137Ba+) via sympathetic cooling with laser-cooled 138Ba+ in a linear radiofrequency trap. The sympathetically cooled species were embedded in the centre of large 138Ba+ Coulomb crystals containing up to 2000 ions and were identified by motional resonance excitation. Crystals with molecular fractions exceeding 70% were obtained. The observed multi-species crystal structures agree well with results from molecular dynamics simulations. The simulations were also used to deduce an upper limit for the translational temperature of the molecular ions, as low as 20 mK.

Upper and lower bounds are estimated for the scattering length, a, for the various isotopes of spin-polarized metastable helium. From a previous study involving various large basis sets and two ab initio approaches, and paying special attention to combine them with the accurate long-range potential, we get, for 4He*–4He* collisions (in Bohr) 152 865. Indeed, the scattering length for this species is very close to the divergence occurring at the binding of a 14th vibrational level. Within these limits, our approach suggests that the values for 4−4a and 3−3a are closer to their upper bounds than to their lower bounds, and that the value for 3−4a is negative and very large (>500) in magnitude. Sympathetic cooling could therefore be very efficient for the mixed species. Cooling-rate coefficients are also evaluated: they are large, of order 10−9 cm3 s−1 at mK temperatures for all combinations.

This thesis presents studies of quantum degenerateatomic gases of fermionic $^6$Li and bosonic $^7$Li. Degeneracy isreached by evaporative cooling of $^7$Li in a strongly confiningmagnetic trap. Since at low temperatures direct evaporativecooling is not possible for a polarized fermionic gas, $^6$Li issympathetically cooled by thermal contact with $^7$Li. In a firstseries of experiments both isotopes are trapped in their low-fieldseeking higher hyperfine states. A Fermi degeneracy of$T/T_F=0.25(5)$ is achieved for $10^5$ fermions. For more than$\sim 300$ atoms, the $^7$Li condensate collapses, due to theattractive interatomic interaction in this state. This limits thedegeneracy reached for both species. To overcome this limit, in asecond series of experiments $^7$Li and $^6$Li atoms aretransferred to their low field seeking lower hyperfine states,where the boson-boson interaction is repulsive but weak. Theinter-isotope collisions are used to thermalize the mixture. A$^7$Li Bose-Einstein condensate (BEC) of $10^4$ atoms immersed ina Fermi sea is produced. The BEC is quasi-one-dimensional and thethermal fraction can be negligible. The measured degeneracies are$T/T_C=T/T_F=0.2(1)$. The temperature is measured using thebosonic thermal fraction, which vanishes at the lowesttemperatures, limiting our measurement sensitivity. In a thirdseries of experiments, the bosons are transferred into an opticaltrap and their internal state is changed to $|F=1,m_F=1\rangle$,the lowest energy state. A Feshbach resonance is detected and usedto produce a BEC with tunable atomic interactions. When theeffective interaction between atoms is tuned to be small andattractive, we observe the formation of a matter-wave brightsoliton. Propagation of the soliton without spreading over amacroscopic distance of $1.1\,$mm is observed., Cette thèse décrit l'étude des gaz de fermions $^6$Li et de bosons$^7$Li dans le régime quantique à très basse température. Lerefroidissement est obtenu par évaporation du $^7$Li dans un piègemagnétique très confinant. Puisque le refroidissement évaporatifd'un gaz de fermion polarisé est quasiment impossible, le $^6$Liest refroidi sympathiquement par contact thermique avec le $^7$Li.Dans une première série d'expériences, les propriétés des gazquantiques dans les états hyperfins les plus élevés, piégésmagnétiquement, sont étudiées. Un gaz de $10^5$ fermions a unetempérature de 0.25(5) fois la température de Fermi ($T_F$) estobtenu. L'instabilité du condensat pour plus de 300 atomescondensés, à cause des interactions attractives, limite ladégénérescence que l'on peut atteindre. Pour s'affranchir de cettelimite, une autre série d'expérience est menée dans les étatshyperfins bas, piégeable magnétiquement, où les interactions entrebosons sont faiblement répulsives. Les collisionsinter-isotopiques permettent alors la thermalisation du mélange.Le mélange d'un condensat de Bose-Einstein (CBE) de $^7$Li et d'unmer de Fermi de $^6$Li est produit. Le condensat est quasiunidimensionnel et la fraction thermique peut être négligeable. Ladégénérescence atteinte correspond à $T/T_C=T/T_F=0.2(1)$. Latempérature est mesurée à partir de la fraction thermique desbosons qui disparaît aux plus basses températures, et limite notreprécision de mesure. Dans une troisième série d'expérience, lesbosons sont transférés dans un piège optique, et placé dans l'étatinterne $|F=1,m_F=1\rangle$, l'état fondamental pour les bosons.Une résonance de Feshbach est repérée puis exploitée pour formerun condensai où les interactions sont ajustables. Quand lesinteractions effectives entre les atomes sont attractives, onobserve la formation d'un soliton brillant de matière. Lapropagation de ce soliton sans dispersion sur une distance de$1.1\,$mm est observée.

In MALDI, electrons were found to be formed by the photoelectric effect on the metal/organic matrix interface. The thin layer of organic matrix reduces the metal work function, resulting in a high electron yield in a field-free MALDI source. These electrons were detected in a FTICR mass spectrometer indirectly, by the observation of SF6 − ions, produced by electron capture. The number and velocity distribution of these electrons were estimated. It is shown that the yield of electrons strongly depends on the thickness of the organic sample. In the case of non-metallic substrates or thick matrix layers, much fewer electrons were detected. Electrons confined in a FTICR trap can cool negative ions produced by MALDI by long range Coulomb interaction, thus increasing the resolving power and sensitivity. (Int J Mass Spectrom 220 (2002) 11–19) © 2002 Elsevier Science B.V. All rights reserved.

We present results on trapping and cooling of positrons in a Penning trap. Positrons from a 2 mCi 22 Na source travel along the axis of a 6 Tmagnet and through the trap after which they strike a Cu reflection moderator crystal. Up to a few thousand positrons are trapped and lose energy through Coulomb collisions (sympathetic cooling) with lasercooled 9 Be þ . By imaging the 9 Be þ laser-induced fluorescence, we observe centrifugal separation of the 9 Be þ ions and positrons, with the positrons coalescing into a column along the trap axis. This indicates the positrons have the same rotation frequency and comparable density (� 4 � 10 9 cm � 3 ) as the 9 Be þ ions, and places an upper limit of approximately 5 K on the positron temperature of motion parallel to the magnetic field. We estimate the number of trapped positrons from the volume of this column and from the annihilation radiation when the positrons are ejected from the trap. The measured positron lifetime is >8 days in our room-temperature vacuum of 10 � 8 Pa. Published by Elsevier Science B.V.

We theoretically investigated the mass dependence of the sympathetic cooling rate of gas-phase ions trapped in a linear radio-frequency-quadrupole ion trap. Using an a priori molecular dynamical calculation, tracing numerically with Newtonian equations of motion, we found that ions with a mass greater than 0.54±0.04 times that of the laser-cooled ions are sympathetically cooled; otherwise, they are heated. To understand the mass dependence obtained using the molecular-dynamical calculation, we made a heat-exchange model of sympathetic cooling, which shows that the factor of 0.54±0.04 is a consequence of absence of micro-motion along the axis of the linear ion trap.

An optically levitated nonspherical nanoparticle can exhibit both librational and translational vibrations due to orientational and translational confinements of the optical tweezer, respectively. Usually, the frequency of its librational mode in a linearly-polarized optical tweezer is much larger than the frequency of its translational mode. Because of the frequency mismatch, the intrinsic coupling between librational and translational modes is very weak in vacuum. Here we propose a scheme to couple its librational and center-of-mass modes with an optical cavity mode. By adiabatically eliminating the cavity mode, the beam splitter Hamiltonian between librational and center-of-mass modes can be realized. We find that high-fidelity quantum state transfer between the librational and translational modes can be achieved with practical parameters. Our work may find applications in sympathetic cooling of multiple modes and quantum information processing., Comment: 6 pages, 3 figures

We generate coherent ultraviolet radiation at 313 nm as the third harmonic of an external-cavity diode laser. We use this radiation for laser cooling of trapped beryllium atomic ions and sympathetic cooling of co-trapped beryllium-hydride molecular ions. An LBO crystal in an enhancement cavity generates the second harmonic, and a BBO crystal in a doubly resonant enhancement cavity mixes this second harmonic with the fundamental to produce the third harmonic. Each enhancement cavity is preceded by a tapered amplifier to increase the fundamental light. The 36-mW output power of this all-semiconductor-gain system will enable quantum control of the beryllium ions' motion.

We present measurements of resistive and sympathetic cooling of ion clouds confined in a Penning trap. For resistive cooling of a cloud consisting of one ion species, we observe a significant deviation from exponential cooling behavior which is explained by an energy-transfer model. The observed sympathetic cooling of simultaneously confined ion species shows a quadratic dependence on the ion charge state and is hence in agreement with expectations from the physics of dilute non-neutral plasmas., 10 figures

We trap cold, ground state argon atoms in a deep optical dipole trap produced by a buildup cavity. The atoms, which are a general source for the sympathetic cooling of molecules, are loaded in the trap by quenching them from a cloud of laser-cooled metastable argon atoms. Although the ground state atoms cannot be directly probed, we detect them by observing the collisional loss of cotrapped metastable argon atoms and determine an elastic cross section. Using a type of parametric loss spectroscopy we also determine the polarizability of the metastable 4s[3/2](2) state to be (7.3±1.1)×10(-39) C m(2)/V. Finally, Penning and associative losses of metastable atoms in the absence of light assisted collisions, are determined to be (3.3±0.8)×10(-10) cm(3) s(-1).

We describe our work on trapping, cooling and detecting mixed ion species for a scalable ion trap quantum information processing architecture. These mixed species chains in linear RF traps may help solve several problems with scaling ion trap quantum computation to large numbers of qubits. Initial temperature measurements of linear Coulomb crystals containing barium and ytterbium ions indicate that the mass difference does not significantly impede sympathetic cooling of normal modes that couple well to the coolant ions (Ba in our case). Average motional occupation numbers are estimated to be 10 to 20 quanta per mode for these well cooled modes for chains with small numbers of ions, consistent with the Doppler limit temperature. For normal modes that do not couple significantly to the coolant atoms, the occupation numbers are significantly higher, of order several thousand. Strategies for better cooling of these modes are discussed. Further, we are working to implement these techniques in microfabricated surface traps in order to exercise greater control over ion chain ordering and positioning.

We report the sympathetic cooling and Coulomb crystallization of molecular ions above the surface of an ion-trap chip. ${\mathrm{N}}_{2}^{+}$ and ${\mathrm{CaH}}^{+}$ ions were confined in a surface-electrode radio-frequency (rf) ion trap and cooled by the interaction with laser-cooled ${\mathrm{Ca}}^{+}$ ions to secular translational temperatures in the millikelvin range. The configuration of trapping potentials generated by the surface electrodes enabled the formation of planar bicomponent Coulomb crystals and the spatial separation of the molecular from the atomic ions on the chip. The structural and thermal properties of the Coulomb crystals were characterized using molecular dynamics simulations. The present study extends chip-based trapping techniques to cold molecular ions with potential applications in mass spectrometry, chemistry, quantum information science, and spectroscopy.

We measure ion heating following transport throughout a Y-junction surface-electrode ion trap. By carefully selecting the trap voltage update rate during adiabatic transport along a trap arm, we observe minimal heating relative to the anomalous heating background. Transport through the junction results in an induced heating between 37 and 150 quanta in the axial direction per traverse. To reliably measure heating in this range, we compare the experimental sideband envelope, including up to fourth-order sidebands, to a theoretical model. The sideband envelope method allows us to cover the intermediate heating range inaccessible to the first-order sideband and Doppler recooling methods. We conclude that quantum information processing in this ion trap will likely require sympathetic cooling in order to support high fidelity gates after junction transport.

Driven dissipative steady state entanglement schemes take advantage of coupling to the environment to robustly prepare highly entangled states. We present a scheme for two trapped ions to generate a maximally entangled steady state with fidelity above 0.99, appropriate for use in quantum protocols. Furthermore, we extend the scheme by introducing detection of our dissipation process, significantly enhancing the fidelity. Our scheme is robust to anomalous heating and requires no sympathetic cooling., 5 pages, 6 figures

We discuss an experimental approach allowing to prepare antihydrogen atoms for the GBAR experiment. We study the feasibility of all necessary experimental steps: The capture of incoming $\bar{\rm H}^{+}$ ions at keV energies in a deep linear RF trap, sympathetic cooling by laser cooled Be+ ions, transfer to a miniaturized trap and Raman sideband cooling of an ion pair to the motional ground state, and further reducing the momentum of the wavepacket by adiabatic opening of the trap. For each step, we point out the experimental challenges and discuss the efficiency and characteristic times, showing that capture and cooling are possible within a few seconds. We discuss an experimental approach allowing to prepare antihydrogen atoms for the GBAR experiment. We study the feasibility of all necessary experimental steps: The capture of incoming $\bar{\rm H}^+$ ions at keV energies in a deep linear RF trap, sympathetic cooling by laser cooled Be$^+$ ions, transfer to a miniaturized trap and Raman sideband cooling of an ion pair to the motional ground state, and further reducing the momentum of the wavepacket by adiabatic opening of the trap. For each step, we point out the experimental challenges and discuss the efficiency and characteristic times, showing that capture and cooling are possible within a few seconds.

This project was superseded and replaced by another ARO-funded project of the same name, which is still continuing. The goal of this project was to explore ultracold collisions and chemistry between atoms and ions, to enable a novel cooling method, proposed by our group, for producing ultracold molecular ions. During this effort period, we experimentally and theoretically studied ultracold chemistry and collision in two important systems Ca + Yb+ and Ca + Ba+. As a result of this work, we have a gained a clearer understanding of both the fundamental physics important for these collisions and the requirements for producing stable, long-lived ultracold ion-neutral systems. Building on this work, we have recently performed a proof-of-principle experiment that has demonstrated sympathetic cooling of both the translational and vibrational motion of BaCl+ molecules through collisions with ultracold gases. The results of this experiment are very promising and indicate that the proposed cooling method is as efficient as expected. Work now has turned to optimizing the experimental system for the production of ultracold, ground-state molecular ions.

We demonstrate a spatial-imaging thermometry technique for ions in a one-dimensional Coulomb crystal by relating their imaged spatial extent along the linear radiofrequency ion trap axis to normal modes of vibration of coupled oscillators in a harmonic potential. We also use the thermal spatial spread of “bright” ions in the case of a two-species mixed chain to measure the center-of-mass resonance frequency of the entire chain and infer the molecular composition of the co-trapped “dark” ions. These non-destructive techniques create new possibilities for better understanding of sympathetic cooling in mixed-ion chains, improving few-ion mass spectrometry, and trapped-ion thermometry without requiring a scan of Doppler cooling parameters.

Antihydrogen, the bound state of an antiproton and a positron, is of interest for use in precision tests of nature's fundamental symmetries. Antihydrogen formed by carefully merging cold plasmas of positrons and antiprotons has recently been trapped in magnetic traps. The efficiency of trapping is strongly dependent on the temperature of the nascent antihydrogen, which, to be trapped, must have a kinetic energy less than the trap depth of . In the conditions in the ALPHA experiment, the antihydrogen temperature seems dominated by the temperature of the positron plasma used for the synthesis. Cold positrons are therefore of paramount interest in that experiment. In this paper, we propose an alternative route to make ultra-cold positrons for enhanced antihydrogen trapping. We investigate theoretically how to extend previously successful sympathetic cooling of positrons by laser-cooled positive ions to be used for antihydrogen trapping. Using simulations, we investigate the effectiveness of such cooling in conditions similar to those in ALPHA, and discuss how the formation process and the nascent antihydrogen may be influenced by the presence of positive ions. We argue that this technique is a viable alternative to methods such as evaporative and adiabatic cooling, and may overcome limitations faced by these. Ultra-cold positrons, once available, may also be of interest for a range of other applications.

We study from the point of view of quantum logic the properties of the collective oscillations of a linear chain of ions trapped in a linear Paul trap and composed of two ion species. We discuss extensively sympathetic cooling of the chain and the effect of anharmonicity on laser-cooling and quantum-information processing.

Superfluidity has become a topic of active interest in the field of atom trap Bose-Einstein condensates (BECs). We motivate this line of research by placing the BEC developments against the general backdrop of the theory of superfluidity and by highlighting the advantages offered by the atom trap technology. We review the standard description of the BEC dynamics, as well as basic concepts of superfluidity and we present theoretical arguments for expecting the BECs to exhibit superfluid behaviour, In atom traps, as in condensed and nuclear matter, superfluidity can manifest itself in a manifold of guises. Moreover, some of its manifestations can even be undesirable, as we illustrate by the poignant example of sympathetic cooling with condensates. We also review recent experimental evidence for superfluid BEC behaviour and we suggest further experiments to probe superfluidity in atom traps. The low densities of the BECs allow optical imaging and imply that the relevant physics occurs on time and length scales that are much slower and larger than in the traditional 4 He superfluid. Consequently, BEC experiments can study known superfluid phenomena and structures in a different and, perhaps, more detailed manner. In addition, the flexibility offered by existing techniques in atomic, molecular and optical physics is unprecedented in the field of low-temperature physics and suggests the prospect of creating superfluids of fundamentally novel structures. Finally, it is conceivable that new applications of superfluidity may arise from these studies.

The investigation of highly charged ion Coulomb crystallization in mixed strongly coupled plasmas is of interest in many areas: white dwarf astrophysical plasmas are believed to have very similar thermodynamic properties, cold highly charged ions can be used as an object for high precision laser spectroscopy of fine and hyperfine transitions in the visible due to the absence of Doppler broadening and, an entirely new area of research is the potential application to highly charged ion based quantum computing schemes.

We have trapped and sympathetically cooled the molecular ions HCO and N2H 1 in a Penning trap. Through their Coulomb interaction with laser-cooled Mg ions the molecules were sympathetically cooled to cryogenic temperatures. We identify the molecules through a measurement of their characteristic massdependent breathing mode frequencies. From a measurement of the temperature of the Mg ions we estimate that the final temperature of the sympathetically cooled molecules is 4 K. @S1050-2947~99!04611-9#

We present theoretical prospects for creating p-wave paired BCS states of magnetic trapped fermionic atoms. Based on our earlier proposal of using dc electric fields to control both the strength and anisotropic characteristic of atom-atom interaction and our recently completed multi-channel atomic collision calculations we discover that p-wave pairing with $^{40}$K and $^{82,84,86}$Rb in the low field seeking maximum spin polarized state represent excellent choices for achieving superfluid BCS states; and may be realizable with current technology in laser cooling, magnetic trapping, and evaporative/sympathetic cooling, provided the required strong electric field can be applied. We also comment on the prospects of similar p-wave paired BCS states in $^{6}$Li, and more generally on creating other types exotic BCS states. Our study will open a new area in the vigorous pursuit to create a quantum degenerate fermionic atom vapor.

Sympathetic cooling of an atomic Fermi gas by a Bose gas is studied by solution of the coupled quantum Boltzmann equations for the confined gas mixture. Results for equilibrium temperatures and relaxation dynamics are presented, and some simple models developed. Our study illustrate that a combination of sympathetic and forced evaporative cooling enables the Fermi gas to be cooled to the degenerate regime where quantum statistics, and mean field effects are important. The influence of mean field effects on the equilibrium spatial distributions is discussed qualitatively., Comment: 8 pages, 9 figures, accepted for publication in Phys.Rev.Lett