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Thorium-229 is a unique case in nuclear physics: it presents a metastable first excited state 229m Th, just a few electronvolts above the nuclear ground state. This so-called isomer is accessible by VUV lasers, which allows transferring the amazing precision of atomic laser spectroscopy to nuclear physics. Being able to manipulate the 229 Th nuclear states at will opens up a multitude of prospects, from studies of the fundamental interactions in physics to applications as a compact and robust nuclear clock. However, direct optical excitation of the isomer or its radiative decay back to the ground state has not yet been observed, and a series of key nuclear structure parameters such as the exact energies and half-lives of the low-lying nuclear levels of 229 Th are yet unknown. Here we present the first active optical pumping into 229m Th. Our scheme employs narrow-band 29 keV synchrotron radiation to resonantly excite the second excited state, which then predominantly decays into the isomer. We determine the resonance energy with 0.07 eV accuracy, measure a half-life of 82.2 ps, an excitation linewidth of 1.70 neV, and extract the branching ratio of the second excited state into the ground and isomeric state respectively. These measurements allow us to re-evaluate gamma spectroscopy data that have been collected over 40 years.

We report measurement of inelastic loss in dense and cold metastable ytterbium (Yb[ 3 P2]). Use of an optical far-off-resonance trap enables us to trap atoms in all magnetic sublevels, removing multichannel collisional trap loss from the system. Trapped samples of Yb[ 3 P2] are produced at a density of 2×10 13 cm −3 and temperature of 2 µK. We observe rapid two-body trap loss of Yb[ 3 P2] and measure the inelastic collision rate constant 1.0(3)×10 −11 cm 3 s −1 . The existence of the finestructure changing collisions between atoms in the 3 P2 state is strongly suggested.PACS numbers: 37.10. De, There is increasing interest in ultracold two-electron atoms [1,2], such as the alkaline earth metals (e.g. Ca and Sr) and Yb. In particular, novel characteristics of the metastable 3 P 2 atoms have recently attracted attention, both for applications and for the study of their collisional properties [3]. These atoms are set apart from the more commonly studied alkali metal atoms because collisions between 3 P 2 atoms are intrinsically anisotropic. Recent theory has investigated the effects of this anisotropy, including its interplay with magnetic field effects, which enable novel control of the scattering length [4], and multichannel collisions due to a strong coupling among the partial waves of relative motion [5,6]. Also, the magnetic dipole-dipole interaction between 3 P 2 atoms is 9 times larger than that between alkali metal atoms. This has led to theoretical predictions such as novel quantum phases and use in quantum information systems [7,8].In order to move toward study of these new possible features of 3 P 2 atoms, several laboratories have realized laser cooling and trapping of metastable two-electron atoms. Ca and Sr atoms decaying to the 3 P 2 state from the 1 P 1 state, which is the upper state in the 1 S 0 ↔ 1 P 1 magneto-optical trap (MOT) transition, have been successfully trapped in a magnetic trap [9]. Also, a MOT operating on the 3 P 2 ↔ 3 D 3 transition has been used to load a magnetic trap [10]. In spite of successes of these approaches, evaporative cooling of 3 P 2 atoms in a magnetic trap to reach Bose-Einstein condensation (BEC) turned out to be unsuccessful due to trap loss caused by strong multichannel collision processes [5]. More recently, a similar large inelastic collision rate in Ca[ 3 P 2 , m J =2] was observed [11].The loss induced by multichannel collisions in a magnetic trap can be overcome by employing, instead of a magnetic trap, an optical far-off-resonance trap (FORT). According to Ref. [12], the FORT wavelength can be chosen so that atoms in every magnetic sublevel of the 3 P 2 state can be trapped with the same strength. As a result, although multichannel collisions can still occur, which distributes the atoms over the different magnetic sublevels, they will not lead to trap loss. Thus, any trap loss observed in such a trap must be due to a different physical mechanism. Study of these collisional properties is crucial to understanding the physics of these important class of atom...

We propose a new quantum-computing scheme using ultracold neutral ytterbium atoms in an optical lattice. The nuclear Zeeman sublevels define a qubit. This choice avoids the natural phase evolution due to the magnetic dipole interaction between qubits. The Zeeman sublevels with large magnetic moments in the long-lived metastable state are also exploited to address individual atoms and to construct a controlled-multiqubit gate. Estimated parameters required for this scheme show that this proposal is scalable and experimentally feasible.