We report the observation of a Bose-Einstein condensation of ytterbium atoms by evaporative cooling in a novel crossed optical trap. Unlike the previously observed condensates, a ytterbium condensate is a two-electron system in a singlet state and has distinct features such as the extremely narrow intercombination transitions which are ideal for future optical frequency standard and the insensitivity to external magnetic field which is important for precision coherent atom optics, and the existence of the novel metastable triplet states generated by optical excitation from the singlet state.

Storage and retrieval of a squeezed vacuum was successfully demonstrated using electromagnetically induced transparency. The squeezed vacuum pulse having a temporal width of 930 ns was incident on the laser cooled 87Rb atoms with an intense control light in a coherent state. When the squeezed vacuum pulse was slowed and spatially compressed in the cold atoms, the control light was switched off. After 3 mus of storage, the control light was switched on again, and the squeezed vacuum was retrieved, as was confirmed using the time-domain homodyne method.

Structure-defined metal-organic frameworks (MOFs) are of interest because rational design and construction allow us to develop good proton conductors or possibly control the proton conductivity in solids. We prepared a highly proton-conductive MOF (NH4)2(adp)[Zn2(ox)3]·nH2O (abbreviated to 1·nH2O, adp: adipic acid, ox: oxalate, n = 0, 2, 3) having definite crystal structures and showing reversible structural transformations among the anhydrate (1), dihydrate (1·2H2O), and trihydrate (1·3H2O) phases. The crystal structures of all of these phases were determined by X-ray crystallography. Hydrogen-bonding networks consisting of ammonium ions, water molecules, and carboxylic acid groups of the adipic acids were formed inside the two-dimensional interlayer space in hydrated 1·2H2O and 1·3H2O. The crystal system of 1 or 1·2H2O (P21/c, No. 14) was changed into that of 1·3H2O (P1̅, No. 2), depending on water content because of rearrangement of guests and acidic molecules. Water molecules play a key role in proton conduction as conducting media and serve as triggers to change the proton conductivity through reforming hydrogen-bonding networks by water adsorption/desorption processes. Proton conductivity was consecutively controlled in the range from ∼10(-12) S cm(-1) (1) to ∼10(-2) S cm(-1) (1·3H2O) by the humidity. The relationships among the structures of conducting pathways, adsorption behavior, and proton conductivity were investigated. To the best of our knowledge, this is the first example of the control of a crystalline proton-conducting pathway by guest adsorption/desorption to control proton conductivity using MOFs.

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