Tests of local position invariance using continuously running atomic clocks
Tests of local position invariance (LPI) made by comparing the relative redshift of atomic clocks based on different atoms have been carried out for a variety of pairs of atomic species. In most cases, several absolute frequency measurements per year are used to look for an annual signal, resulting in tests that can span on order of a decade. By using the output of continuously running clocks, we carry out LPI tests with comparable or higher precision after less than 1.5 years. These include new measurements of the difference in redshift anomalies β for hyperfine transitions in Rb87 and Cs133 and in H and Cs133 and a measurement comparing Rb87 and H, resulting in a stringent limit on LPI, β(Rb) - β(H)=(-2.7 +/- 4.9) x 10^(-7). The method of making these measurements for continuous clocks is discussed.