- Conference date: 25-30 July 2004
- Location: Rio de Janeiro (Brazil)
A comparison of different atomic frequency standards over time can be used to perform a measurement of the present value of the temporal derivative of the fine structure constant α in a model‐independent way without assumptions on constancy or variability of other parameters. We have measured an optical transition frequency at 688 THz in Yb+ with a cesium atomic clock at two times separated by 2.8 years and find that a variation of this frequency can be excluded within a 1σ relative uncertainty of 4.4⋅10−15 yr−1. Combined with recently published values for the constancy of other transition frequencies this measurement provides a limit on the present variability of α at the level of 2.0⋅10−15 yr−1. Constraints are also derived for the drift rates of other fundamental constants like the electron/proton mass ratio and the proton g‐factor.
- Atomic fine structure
- Atomic clocks
- Frequency measurement
- Frequency standards
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