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We present an extended model for the lattice-induced light shifts of the clock frequency in optical lattice clocks, applicable to a wide range of operating conditions. The model extensions cover radial motional states with sufficient energies to invalidate the harmonic approximation of the confining potential. We reevaluate lattice-induced light shifts in our Yb optical lattice clock with an uncertainty of 6.1E-18 under typical clock operating conditions., Comment: 12 pages, 10 figures

We introduce a description of Ramsey spectra under atomic interactions as a sum of decomposed components with differing dependence on interaction parameters. This description enables intuitive understanding of the loss of contrast and asymmetry of Ramsey spectra. We derive a quantitative relationship between the asymmetry and atomic interaction parameters, which enables their characterization without changing atom density. The model is confirmed through experiments with a Yb optical lattice clock.

We implemented a compact, robust, and stable device for simultaneous frequency stabilization of lasers with different wavelengths used for the cooling and trapping of Yb atoms in an optical lattice clock. The lasers at 399, 556, and 759 nm are locked to a single ultra-stable cavity using the offset sideband locking technique, a modified version of the Pound-Drever-Hall method. For the most demanding stabilization here, the 556 nm laser, this system exhibits a 300 Hz linewidth for an integration time of 80 ms. We observed a long-term drift of less than 20 kHz per day at 759 nm that is suitable for operating the lattice laser with a light shift uncertainty below 1×10sup-18/sup. We successfully tested the system for operating the clock during a typical working day by simultaneously locking the three lasers to the cavity.

Nowadays atomic optical lattice clocks can perform frequency measurements with a fractional uncertainty at the 10-18 level in few hours of measurement, outperforming the best caesium (Cs) standards operated in the world. Since the definition of the unit of time is based on Cs, a worldwide debate about the need to promote the redefinition of the second on a optical reference is under-way. At INRIM (Istituto Nazionale di Ricerca Metrologica) we developed an optical lattice clock based on ytterbium atoms and compared it against a Cs fountain. These results are an important contribution to the debate.

We present the results of a preliminary metrological characterization of our neutral 171Ytterbium-atoms lattice clock at INRIM. During one clock cycle we cool and trap the atoms utilizing 399 nm laser light for the first stage magneto-optical trap (MOT), followed by a cooler 556 nm 2nd stage MOT. Atoms are then transferred in a one-dimensional, horizontal lattice adjusted to the magic wavelength (759 nm). Subsequently the clock transition at 578 nm is excited by a laser stabilized to an ultra-stable cavity, followed by repumping and state-detection. We obtain 2 · 103 atoms in the lattice after 150 ms of loading time. The laser radiation at 399 nm, 556 nm and 578 nm is produced via infrared lasers and non-linear crystals, whereas the lattice features a Titanium-Sapphire laser. A detailed description of the laser light generation and stabilization as well as of the the physics package is given. We locked the clock laser to the atoms and achieved a first metrological characterization through optical fiber-comb based comparison with INRIM's primary frequency standard, the IT-CsF2 cryogenic fountain clock [1]. The reported frequency of the clock transition agrees to the value recommended by the BIPM [2] within the stated uncertainty.

We present an optical lattice clock based on ytterbium 171Yb atoms developed in the laboratories of INRIM. In the experiment, we cool and trap ytterbium atoms in a two stage magneto-optical trap (MOT) (at 399nm and 556nm for the first and second stage, respectively). Atoms are then transferred in a horizontal, one-dimensional optical lattice at the magic wavelength (759 nm). Here the clock transition at 578nm is probed by a laser stabilized on an ultra-stable cavity. We describe the generation of all the laser sources, the physic package and the operation of the clock. Lasers at 399 nm, 556nm and 578nm are obtained, with different techniques, using non-linear crystals starting from infrared sources. The clock laser is stabilized using a high finesse notched ULE cavity. The lattice is made with a titanium-sapphire laser. The aluminum vacuum chamber is designed for wide optical access and its temperature is measured by 8 thermistors for blackbody shift evaluation. Our system allows for fast loading of the lattice with 1 × 104 atoms trapped in the lattice in 250 ms. We obtained preliminary spectroscopy results and we locked the clock laser to the atomic line. Future perspectives are discussed.