We report direct single-laser excitation of the strictly forbidden (6s2)1S0 <--> (6s6p)3P0 clock transition in 174Yb atoms confined to a 1D optical lattice. A small (approximately 1.2 mT) static magnetic field was used to induce a nonzero electric dipole transition probability between the clock states at 578.42 nm. Narrow resonance linewidths of 20 Hz (FWHM) with high contrast were observed, demonstrating a resonance quality factor of 2.6 x 10(13). The previously unknown ac Stark shift-canceling (magic) wavelength was determined to be 759.35 +/- 0.02 nm. This method for using the metrologically superior even isotope can be easily implemented in current Yb and Sr lattice clocks and can create new clock possibilities in other alkaline-earth-like atoms such as Mg and Ca.
We develop a method of spectroscopy that uses a weak static magnetic field to enable direct optical excitation of forbidden electric-dipole transitions that are otherwise prohibitively weak. The power of this scheme is demonstrated using the important application of optical atomic clocks based on neutral atoms confined to an optical lattice. The simple experimental implementation of this method--a single clock laser combined with a dc magnetic field--relaxes stringent requirements in current lattice-based clocks (e.g., magnetic field shielding and light polarization), and could therefore expedite the realization of the extraordinary performance level predicted for these clocks. We estimate that a clock using alkaline-earth-like atoms such as Yb could achieve a fractional frequency uncertainty of well below 10(-17) for the metrologically preferred even isotopes.
We present an experimental study of the lattice induced light shifts on the 1 S0 → 3 P0 optical clock transition (ν clock ≈ 518 THz) in neutral ytterbium. The "magic" frequency, νmagic, for the 174 Yb isotope was determined to be 394 799 475(35)MHz, which leads to a first order light shift uncertainty of 0.38 Hz on the 518 THz clock transition. Also investigated were the hyperpolarizability shifts due to the nearby 6s6p 3 P0 → 6s8p 3 P0, 6s8p 3 P2, and 6s5f 3 F2 two-photon resonances at 759.708 nm, 754.23 nm, and 764.95 nm respectively. By tuning the lattice frequency over the twophoton resonances and measuring the corresponding clock transition shifts, the hyperpolarizability shift was estimated to be 170(33) mHz for a linear polarized, 50 µK deep, lattice at the magic wavelength. In addition, we have confirmed that a circularly polarized lattice eliminates the J = 0 → J = 0 two-photon resonance. These results indicate that the differential polarizability and hyperpolarizability frequency shift uncertainties in a Yb lattice clock could be held to well below 10 −17 .
We report the first observation of anti-Stokes fluorescence cooling in a thulium-doped solid with pump excitation at 1.82 mm , l , 1.97 mm. At a pump wavelength of 1.9 mm and incident average power of ϳ3 W, a Tm 31 :ZBLANP (ZrF 4-BaF 2-LaF 3-AlF 3-NaF-PbF 2) sample cooled to 21.2 ± C from room temperature for a single pass of the pump beam. This corresponds to an absorbed pump power of ϳ40 mW and a peak temperature change per absorbed power of ϳ 230 ± C͞W from room temperature.
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