Optical Lattice Clock with Fermionic Strontium

We present recent results from our optical atomic clock based on neutral $^{87}$Sr in an optical lattice. By probing the ${{^1}\mathrm{S}_0}$-${{^3}\mathrm{P}_0}$ clock transition with a sub-Hz linewidth diode laser, we recover spectra with quality factors $Q > 2\times 10^{14}$. The clock frequency was measured as $429\,228\,004\,229\,874.0 (1.1)$~Hz, with systematic uncertainty $<9\times10^{-16}$, a level of performance approaching current Cs fountains. Stability is currently limited by the Cs-fountain-calibrated hydrogen maser used as the frequency standard. The measured frequency agrees well with our previous data as well as recent measurements by the Paris and Tokyo groups. Work toward direct comparison of optical frequency standards is in progress.