Frequency Ratio of Two Optical Clock Transitions in 171Yb+ and Constraints on the Time Variation of Fundamental Constants

Singly ionized ytterbium, with ultranarrow optical clock transitions at 467 and 436 nm, is a convenient system for the realization of optical atomic clocks and tests of present- day variation of fundamental constants. We present the first direct measurement of the frequency ratio of these two clock transitions, without reference to a cesium primary standard, and using the same single ion of Yb-171(+). The absolute frequencies of both transitions are also presented, each with a relative standard uncertainty of 6 x 10(-16). Combining our results with those from other experiments, we report a threefold improvement in the constraint on the time variation of the proton-to-electron mass ratio, (mu) over dot/mu = 0.2(1.1) x 10(-16) yr(-1), along with an improved constraint on time variation of the fine structure constant, (alpha) over dot/alpha = -0.7(2.1) x 10(-17) yr(-1).