Optical lattice clocks with bosonic/fermionic Sr and with the other atomic elements

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To date, optical clocks based on singly trapped ions1) and ultracold neutral atoms trapped in the Stark-shift-free optical lattices2) are regarded as promising candidates for future atomic clocks. So far “optical lattice clocks” have been evaluated with uncertainty of 1×10-15 (ref. 3)) limited by that of Cs atomic clocks. Frequency comparison between highly-stable and accurate optical lattice clocks is, therefore, crucial for their further evaluation. Looking toward fractional uncertainties of 10-16 and below, collisional frequency shift, Black body radiation (BBR) shift, and hyperpolarizability effects, all of which depend on interrogated atomic elements and experimental configurations, are becoming major concerns. In this talk, we discuss optimal lattice geometries in view of the quantum statistics and related spins of interrogated atoms. This leads to two promising configurations for the lattice clock: One-dimensional (1D) lattice loaded with spin-polarized fermions4) and 3D lattice loaded with bosons. We present frequency comparison of these two optical lattice clocks using fermionic 87Sr and bosonic 88Sr. Such lattice clock comparison will offer an important step to ascertain the clocks’ uncertainty beyond the Cs limit of 1×10-15. As for the latter two issues, the BBR and the lattice laser related uncertainties, we discuss prospects for a cryogenic clock, a “blue-detuned” magic wavelength, and a Hg based optical lattice clock5). References: 1) T. Rosenband et al., Science 319 (2008) 1808. 2) H. Katori, M. Takamoto, V. G. Pal\'chikov and V. D. Ovsiannikov, Phys. Rev. Lett. 91 (2003) 173005. 3) S. Blatt et al., Phys. Rev. Lett. 100 (2008) 140801. 4) M. Takamoto et al., J. Phys. Soc. Jpn. 75 (2006) 104302