Yb Lattice Clock

Due to their high oscillation frequency (~10¹⁵ Hz) optical clocks can achieve extremely high spectroscopic line Q's in appropriately prepared atomic samples. As a result, such clocks are reaching levels of clock performance that are orders of magnitude better than was possible only a decade ago. Of particular promise are clocks based on laser-cooled neutral atoms that are confined to an optical lattice, which suppresses Doppler shifts and is designed to minimize clock shifts. In our experiments we have trapped tens of thousands of ¹⁷¹Yb atoms, which have an ultra-narrow transition at 578 nm that we excite with a pre-stabilized laser. We lock the frequency of the probe laser to the spectroscopic feature, which can be as narrow as 1 Hz (full width- half maximum). Through comparisons between two such Yb lattice clocks, we have demonstrated a fractional clock instability for averaging time, τ, of 3 x 10^-16 τ^-1/2, reaching an imprecision of 1.6 x 10^-18 after about 6 hours. A previous evaluation of the fermionic version (¹⁷¹Yb) of the Yb lattice clock yielded a total fractional frequency uncertainty of 3 x 10^-16, however we anticipate a significantly reduced uncertainty in the near future. Of particular experimental interest is the minimization of clock shifts due to blackbody radiation from the lattice surroundings.