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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.

We report coherent enhancement of two-photon emission from the excited vibrational state of molecular hydrogen triggered by irradiating mid-infrared pulses externally. We previously observed the two-photon emission triggered by the internally generated fourth Stokes photons.By injecting independent mid-infrared pulses externally, it is possible to control experimental parameters and investigate the mechanism in more detail. In this article, we describe the twophoton emission using the external trigger pulses. Its spectrum and dependence on the energy and timing of the trigger pulse are presented along with numerical simulations based on the Maxwell-Bloch equations. The measured number of emitted photons is 6×10 11 photons/pulse and the resulting enhancement factor from the spontaneous emission is more than 10 18 . This value is three orders of magnitude higher than that of the previous experiment. External control of emission process is expected to be essential for observation of weaker process of radiative emission of neutrino pair.

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Spin-polarized metastable atoms of ultracold ytterbium are trapped at high density and their inelastic collisional properties are measured. We reveal that in collisions of Yb( 3 P 2 ) with Yb( 1 S 0 ) there is relatively weak inelastic loss, but with a significant spin dependence consistent with Zeeman sublevel changes as being the dominant decay process. This is in strong contrast to our observations of Yb( 3 P 2 )-Yb( 3 P 2 ) collisional losses, which are, at low field, much more rapid and have essentially no spin dependence. Our results give a guideline to using the 3 P 2 states in many possible applications.

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 7×10 3 atoms, 640 µK for 6 Li, 7×10 4 atoms and 60 µK for 174 Yb, respectively.Send offprint requests to: M. Okano,