87Sr optical lattice clocks at JILA

We describe recent experimental progress with the JILA Sr optical frequency standard, which has a systematic uncertainty at the 10
^-16
fractional frequency level, currently limited by frequency shifts due to atomic interactions and room temperature blackbody radiation (BBR). We will discuss systematic measurements of collisional shifts and provide a complete theory to understand these interaction effects at the 10
^-17
level. We will also discuss plans to interrogate atoms inside a cryogenic shield region to eliminate BBR shifts. We will present our recent successful efforts in improving the laser stability with the aim for the JILA Sr standard to reach the standard quantum measurement limit and achieve record levels of stability. Finally, a second Sr optical lattice clock has been constructed at JILA, and we will discuss the results of intercomparison experiments between the two standards.