We use a Feshbach resonance to tune the scattering length a of a Bose-Einstein condensate of 7Li in the |F=1,mF=1> state. Using the spatial extent of the trapped condensate, we extract a over a range spanning 7 decades from small attractive interactions to extremely strong repulsive interactions. The shallow zero crossing in the wing of the Feshbach resonance enables the determination of a as small as 0.01 Bohr radii. Evidence of the weak anisotropic magnetic dipole interaction is obtained by comparison with different trap geometries for small a.

We demonstrate arbitrary coherent addressing of individual neutral atoms in a 5×5×5 array formed by an optical lattice. Addressing is accomplished using rapidly reconfigurable crossed laser beams to selectively ac Stark shift target atoms, so that only target atoms are resonant with state-changing microwaves. The effect of these targeted single qubit gates on the quantum information stored in nontargeted atoms is smaller than 3×10^{-3} in state fidelity. This is an important step along the path of converting the scalability promise of neutral atoms into reality.

Antiferromagnetism of ultracold fermions in an optical lattice can be detected by Bragg diffraction of light, in analogy to the diffraction of neutrons from solid-state materials. A finite sublattice magnetization will lead to a Bragg peak from the ( 1 2 1 2 1 2 ) crystal plane with an intensity depending on details of the atomic states, the frequency and polarization of the probe beam, the direction and magnitude of the sublattice magnetization, and the finite optical density of the sample. Accounting for these effects we make quantitative predictions about the scattering intensity and find that with experimentally feasible parameters the signal can be readily measured with a CCD camera or a photodiode and used to detect antiferromagnetic order.

We have used the narrow 2S 1/2 → 3P 3/2 transition in the ultraviolet (uv) to laser cool and magneto-optically trap (MOT) 6 Li atoms. Laser cooling of lithium is usually performed on the 2S 1/2 → 2P 3/2 (D2) transition, and temperatures of ∼300 μK are typically achieved. The linewidth of the uv transition is seven times narrower than the D2 line, resulting in lower laser cooling temperatures. We demonstrate that a MOT operating on the uv transition reaches temperatures as low as 59 μK. Furthermore, we find that the light shift of the uv transition in an optical dipole trap at 1070 nm is small and blueshifted, facilitating efficient loading from the uv MOT. Evaporative cooling of a two spin-state mixture of 6 Li in the optical trap produces a quantum degenerate Fermi gas with 3 × 10 6 atoms in a total cycle time of only 11 s. The creation of quantum degenerate gases using all-optical techniques [1-4] offers several advantages over methods employing magnetic traps. Optical potentials can trap any ground state, allowing selection of hyperfine sublevels with favorable elastic and inelastic scattering properties. In the case of Fermi gases, the ability to trap atoms in more than one sublevel eliminates the need for sympathetic cooling with another species [5,6], greatly simplifying the experimental setup. All-optical methods also facilitate rapid evaporative cooling since magnetically tunable Feshbach resonances can be employed to achieve fast thermalization.There are, however, challenges to all-optical methods. An essential prerequisite is an optical potential whose depth is sufficiently greater than the temperature of the atoms being loaded. The usual starting point is a laser cooled atomic gas confined to a magneto-optical trap (MOT). In a twolevel picture, atoms may be cooled to the Doppler limit T D =h /(2k B ), where /(2π ) is the natural linewidth of the excited state of the cooling transition [7,8]. In many cases, however, sub-Doppler temperatures can be realized due to the occurrence of polarization gradient cooling arising from the multilevel character of real atoms [9]. Polarization gradient cooling mechanisms are effective if the linewidth of the cooling transition is small compared to the hyperfine splitting of the excited state, or if there is a large degree of magnetic degeneracy in the ground state [10]. The limit to cooling in these cases is the recoil temperature T R =h 2 k 2 /(2mk B ), where k is the wave number of the laser cooling transition and m is the mass of the atom.Polarization gradient cooling is found to be efficient for most of the alkali-metal atoms including Na, Rb, and Cs; MOTs of these species routinely attain temperatures of ∼10 μK, which is not far above T R . Unfortunately, for Li and K, the elements most often employed in Fermi-gas experiments, sub-Doppler cooling is ineffective in the presence of magnetic fields, including those required for a MOT. For Li, sub-Doppler cooling is inhibited because the hyperfine splitting of the excited state is unresolved (Fig. 1), thus limiting ...

Gas-phase organoactinyl complexes possessing discrete An−C bonds (An = U, Np, Pu) were synthesized in a quadrupole ion trap by endothermic decarboxylation of [AnO 2 (O 2 C−R) 3 ]− anion complexes in which a formally AnO 2 2+ actinyl core is coordinated by three carboxylate ligands, with R = CH 3 (methyl), CH 3 CC (1-propynyl), C 6 H 5 (phenyl), C 6 F 5 (pentafluorophenyl). Decarboxylation and competing ligand loss were studied computationally by density functional theory complementing experiment. Although decarboxylation was computed to be the energetically most favorable process in all cases, reduction from An(VI) to An(V) via neutral ligand loss was often prevalent, particularly for An = Np, Pu, presumably resulting from barriers associated with decarboxylation. Comparative hydrolysis rates of the An−C bonds were experimentally determined, and the chemical properties of these bonds were analyzed by the quantum theory of atoms in molecules. The measured hydrolysis rates differed by up to 3 orders of magnitude: the fastest was for [(CH 3 CC)UO 2 (O 2 C− CCCH 3 ) 2 ]− and the slowest for [(C 6 F 5 )PuO 2 (O 2 C−C 6 F 5 ) 2 ]− . There is a general correlation between hydrolysis exothermicity and hydrolysis rate. Prototypical hydrolysis reaction pathways computed for R = CH 3 (An = U, Np) reveal a mechanism in which an outer-sphere water becomes inner-sphere concomitant with transfer of an H atom to yield an OH ligand and CH 4 , with a net energy release of 170 kJ mol −1 and a transition state barrier of 45 kJ mol −1 for An = U. Infrared multiphoton dissociation spectra of selected complexes were acquired to confirm the predicted structures by agreement between the computed and observed vibrational frequencies. The experiment and theory results provide an evaluation of the comparative propensities for formation of the organoactinyls as a function of actinide and carboxylate and an assessment of the nature and stability toward hydrolysis of the primarily ionic An−C bonds.

We demonstrate 3D microwave projection sideband cooling of trapped, neutral atoms. The technique employs state-dependent potentials that enable microwave photons to drive vibration-number reducing transitions. The particular cooling sequence we employ uses minimal spontaneous emission, and works even for relatively weakly bound atoms. We cool 76% of atoms to their 3D vibrational ground states in a site-resolvable 3D optical lattice.

The synthesis, reactivity, structures, and bonding in gas-phase binary and complex oxide anion molecules of protactinium and uranium have been studied by experiment and theory. The oxalate ions, AnVO2(C2O4)−, where An = Pa or U, are essentially actinyl ions, AnVO2 +, coordinated by an oxalate dianion. Both react with water to yield the pentavalent hydroxides, AnVO­(OH)2(C2O4)−. The chemistry of Pa and U becomes divergent for reactions that result in oxidation: whereas PaVI is inaccessible, UVI is very stable. The UVO2(C2O4)− complex exhibits a remarkable spontaneous exothermic replacement of the oxalate ligand by O2 to yield UO4 – and two CO2 molecules. The structure of the uranium tetroxide anion is computed to correspond to distorted uranyl, UVIO2 2+, coordinated in the equatorial plane by two equivalent O atoms each having formal charges of −1.5 and U–O bond orders intermediate between single and double. The unreactive nature of PaVO2(C2O4)− toward O2 is a manifestation of the resistance toward oxidation of PaV, and clearly reveals the disparate chemistries of Pa and U. The uranium tetroxide anion, UO4 –, reacts with water to yield UO5H2 –. Infrared spectra obtained for UO5H2 – confirm the computed lowest-energy structure, UO3(OH)2 –.

Past studies of fragmentation reactions of doubly-charged uranyl (UO2 2+ ) complexes have been impeded by very rapid water addition reactions that cause H2O adducts to dominate product ion spectra.The fragmentation of uranyl-acetone (aco) complexes ([UO2(aco)n] 2+ , n=1-5), generated by electrospray ionization, is revisited here using: (a) collisional activation in a linear ion trap (LIT) mass spectrometer in which the level of background H2O is significantly lower, and (b) infrared photodissociation (IRMPD, 10.6 µm) in the LIT and a Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometer. Lower levels of adventitious H2O in the LIT provided access to fragmentation of [UO2(aco)n] 2+ , n=1-5. For n=3-5, direct elimination of aco ligands is the favored fragmentation pathway. For n=1 and 2, charge reduction reactions are dominant. For [UO2(aco)2] 2+ , the most abundant product ion is [UO2(aco)] + , while UO2 + is observed following collision-induced dissociation (CID) of [UO2(aco)] 2+ . Minor peaks corresponding to ligated [UO2OH] + are also observed. The IRMPD experiments in the FT-ICR yielded highly accurate mass measurements that confirm composition assignments, and shed light on dissociation reactions in a gasphase environment that is entirely free of adventitious H2O. For [UO2(aco)n] 2+ , n=3-5, the primary photodissociation channel is direct aco elimination, along with charge-reduction pathways that involve intra-complex proton transfer and formation of species that contain enolate ligands. Similar pathways are observed for IRMPD measurements in the LIT.