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 171Yb+. The absolute frequencies of both transitions are also presented, each with a relative standard uncertainty of 6×10(-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, μ/μ=0.2(1.1)×10(-16)  yr(-1), along with an improved constraint on time variation of the fine structure constant, α/α=-0.7(2.1)×10(-17)  yr(-1).

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An absolute frequency measurement has been made of the 2 S 1/2 -2 F 7/2 electric octupole transition in a single ion of 171 Yb + . The implementation of a diode-based probe laser stabilized to this highly forbidden transition has resulted in an improvement of more than one order of magnitude upon the lowest published uncertainty. After correcting for systematic shifts, the frequency was determined to be 642 121 496 772 646.22 (67) Hz. This corresponds to a fractional uncertainty of 1.0 × 10 −15 .

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Precision measurements of quantum defects in the Rydberg states of Rb B Sanguinetti, H O Majeed, M L Jones et al. -Frequency metrology in the near-infrared spectrum of H217O and H218O molecules: testing a new inversion method for retrieval of energy levels A Gambetta, E Fasci, A Castrillo et al. Abstract. A three-step laser excitation scheme is used to make absolute frequency measurements of highly excited nF 7/2 Rydberg states in 85 Rb for principal quantum numbers n = 33-100. This work demonstrates the first absolute frequency measurements of rubidium Rydberg levels using a purely optical detection scheme. The Rydberg states are excited in a heated Rb vapour cell and Doppler-free signals are detected via purely optical means. All of the frequency measurements are made using a wavemeter that is calibrated against a Global Positioning System (GPS)-disciplined self-referenced optical frequency comb. We find that the measured levels have a very high frequency stability, and are especially robust against electric fields. The apparatus has allowed measurements of the states to an accuracy of 8.0 MHz. The new measurements are analysed by extracting the modified Rydberg-Ritz series parameters.