Abstract
We compare two optical clocks based on the ^{2}S_{1/2}(F=0)→^{2}D_{3/2}(F=2) electric quadrupole (E2) and the ^{2}S_{1/2}(F=0)→^{2}F_{7/2}(F=3) electric octupole (E3) transition of ^{171}Yb^{+} and measure the frequency ratio ν_{E3}/ν_{E2}=0.932829404530965376(32), improving upon previous measurements by an order of magnitude. Using two caesium fountain clocks, we find ν_{E3}=642121496772645.10(8) Hz, the most accurate determination of an optical transition frequency to date. Repeated measurements of both quantities over several years are analyzed for potential violations of local position invariance. We improve by factors of about 20 and 2 the limits for fractional temporal variations of the fine structure constant α to 1.0(1.1)×10^{-18}/yr and of the proton-to-electron mass ratio μ to -8(36)×10^{-18}/yr. Using the annual variation of the Sun's gravitational potential at Earth Φ, we improve limits for a potential coupling of both constants to gravity, (c^{2}/α)(dα/dΦ)=14(11)×10^{-9} and (c^{2}/μ)(dμ/dΦ)=7(45)×10^{-8}.
Highlights
Searches for violations of Einstein’s equivalence principle, such as tests of local Lorentz invariance and local position invariance (LPI), have become one of the leading applications of low-energy high-precision experiments with laser-cooled atoms or ions [1]
While theories beyond the standard model predict temporal variations of fundamental constants [3] and astronomical observations indicate a spatial variation of the fine structure constant α [4], no experimental observation of any violation of LPI in a laboratory setting has been reported so far [1]
While a small frequency uncertainty of the clock is a prerequisite to reveal undetected indications of physics beyond the standard model, it is of similar importance to have a large sensitivity of the measured quantity, i.e., the frequency ratio of the clocks used in the search, to the potentially varying constant
Summary
Searches for violations of Einstein’s equivalence principle, such as tests of local Lorentz invariance and local position invariance (LPI), have become one of the leading applications of low-energy high-precision experiments with laser-cooled atoms or ions [1]. Promising test cases in tabletop experiments are comparisons of atomic clocks based on transitions that show a different dependence of their frequency on the value of fundamental constants [5,6,7,8,9].
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