A laboratory search for variation of the fine-structure constant using atomic dysprosium

Electric-dipole transitions between nearly degenerate, opposite parity levels of atomic dysprosium (Dy) were monitored overan eight-month period to search for a variation in thefine-structure constant, α. The frequencies of thesetransitions are sensitive to variation of α due to largerelativistic corrections of opposite sign for the opposite-paritylevels. In this unique system, in contrast to atomic-clockcomparisons, the difference of the electronic energies of theopposite-parity levels can be monitored directly utilizing aradio-frequency (rf), electric-dipole transition between them. Ourmeasurements for the frequency variation of the 3.1-MHz transitionin 163Dy and the 235-MHz transition in 162Dy can beanalyzed for both a temporal variation and a gravitational-potentialdependence of α since, during the data acquisition period, the Earth is located at different values of the gravitationalpotential of the Sun. The data provide a rate of fractional temporalvariation of α of (-2.7±2.6)×10-15 yr-1 ora value of (-8.7 ±6.6) ×10-6 for kα, thelinear-variation coefficient for α in a changinggravitational potential. These results are independent ofassumptions regarding variation of other fundamental constants. Thelatter result can be combined with other experimental constraints toextract the first limits on ke and kq, which characterize thevariation of me/mp and mq/mp in a changing gravitationalpotential, where me, mp, and mq are electron, proton, andquark masses. All results indicate the absence of significantvariation at the present level of sensitivity.