Two independent strontium optical lattice clocks for practical realization of the meter and secondary representation of the second

We report a system of two independent strontium optical lattice standards probed with a single shared ultra-narrow laser. This allows verification of relative stability of both optical standards. The absolute frequency of the clocks can be roughly verified by the use of an optical frequency comb with the GPS-disciplined Rb frequency standard or, more accurately, by a long distance stabilized fiber optic link with the UTC(AOS) and UTC(PL) via the OPTIME network.