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We present an experimental study of the lattice induced light shifts on the 1S_0-3P_0 optical clock transition (v_clock~518 THz) in neutral ytterbium. The ``magic'' frequency, v_magic, for the 174Yb 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 3P_0 - 6s8p 3P_0, 6s8p 3P_2, and 6s5f 3F_2 two-photon resonances at 759.708 nm, 754.23 nm, and 764.95 nm respectively. By tuning the lattice frequency over the two-photon resonances and measuring the corresponding clock transition shifts, the hyperpolarizability shift was estimated to be 170(33) mHz for a linear polarized, 50 uK 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., Accepted to PRL

This talk presents two different types of neutral atom optical clocks and emphasizes the systems' differences in potential performance and complexity. Approaches in attaining high stability, high accuracy, and transportable optical atomic clocks are discussed in detail.

We report on two optical clocks: one uses freely expanding calcium atoms, while the other is based on lattice-confined ytterbium. We measure a fractional instability between the clocks of 4 x 10-16@ 100 s.

The paper describes two types of optical atomic clocks. The first is based on freely expanding calcium atoms and is optimized for experimental simplicity and high stability. The second is based on Yb atoms confined to an optical lattice that is designed to yield minimal shifts for the clock transition at 578 nm. Measurements of the effective beatnote between the clocks via a femtosecond-laser frequency comb show a fractional frequency instability of

We report direct single-laser excitation of the strictly forbidden clock transition in atoms confined to a 1D optical lattice. A small () 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 . The previously unknown ac Stark shift-canceling (magic) wavelength was determined to be . 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 report high resolution spectroscopy of optical lattice-confined 174Yb atoms. We demonstrate spectroscopic linewidths as narrow as 4 Hz (full-width at half-maximum) using the highly forbidden clock transition (1S0-3P0) in a one-dimensional optical lattice.

We report the first spectroscopy of optical lattice-confined Yb atoms. We demonstrate 20 Hz linewidths using the highly forbidden clock transition (1S 0 -3P 0 ) in metrologically superior even-isotope 174Yb atoms in a one-dimensional optical lattice.

This work has focused on two atoms, Sr and Yb, due in part to the relatively high abundance of their odd isotopes, the use of which is necessary for appreciable direct excitation probability. The Sr clock transition has been measured (with an uncertainty of 20 kHz) using atoms in a magneto-optic trap (MOT), and has been excited with atoms confined in a one dimensional lattice. Here we report direct excitation of the Yb clock transition (at 578 nm) with atoms in a second-stage MOT, and the first fs-laser comb-based absolute measurements of the clock frequency for two different isotopes. These measurements lead to a nearly millionfold improvement in our knowledge of the transition frequencies, an important step toward Doppler-free spectroscopy of Yb atoms in a lattice.

We report the direct excitation of the highly forbidden $(6{s}^{2})^{1}S_{0}\ensuremath{\leftrightarrow}(6s6p)^{3}P_{0}$ optical transition in two odd isotopes of neutral ytterbium. As the excitation laser frequency is scanned, absorption is detected by monitoring the depletion from an atomic cloud at $\ensuremath{\sim}70\text{ }\text{ }\ensuremath{\mu}\mathrm{K}$ in a magneto-optical trap. The measured frequency in $^{171}\mathrm{Yb}$ ($\mathrm{F}=1/2$) is $518\text{ }295\text{ }836\text{ }591.6\ifmmode\pm\else\textpm\fi{}4.4\text{ }\text{ }\mathrm{kHz}$. The measured frequency in $^{173}\mathrm{Yb}$ ($\mathrm{F}=5/2$) is $518\text{ }294\text{ }576\text{ }847.6\ifmmode\pm\else\textpm\fi{}4.4\text{ }\text{ }\mathrm{kHz}$. Measurements are made with a femtosecond-laser frequency comb calibrated by the National Institute of Standards and Technology cesium fountain clock and represent nearly a ${10}^{6}$-fold reduction in uncertainty. The natural linewidth of these $J=0$ to $J=0$ transitions is calculated to be $\ensuremath{\sim}10\text{ }\text{ }\mathrm{mHz}$, making them well suited to support a new generation of optical atomic clocks based on confinement in an optical lattice.

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.

At the previous Symposium on Frequency Standards and Metrology, H. Katori proposed using IS0 ---->3pO transitions in alkaline earth like atoms to make high performance optical clocks based on large numbers of neutral atoms tightly confined in an optical lattice. 1 This proposal was based on the use of Sr atoms, as were the initial experiments.24 In 2004 Porsev et al. proposed the use of the analogous transition in Yb at 578 nm,5 and we have been developing lattice clocks based on Yb over the past four years. While there are considerable similarities between the Sr and Yb atomic systems, there are also some important differences. Most significantly, Yb has an