Improved Tests of Local Position Invariance Using ^{87}Rb and ^{133}Cs Fountains (original) (raw)
Related papers
Search for Variations of Fundamental Constants using Atomic Fountain Clocks
Physical Review Letters, 2003
Over five years we have compared the hyperfine frequencies of 133 Cs and 87 Rb atoms in their electronic ground state using several laser cooled 133 Cs and 87 Rb atomic fountains with an accuracy of ∼ 10 −15 . These measurements set a stringent upper bound to a possible fractional time variation of the ratio between the two frequencies : d dt ln ν Rb ν Cs = (0.2 ± 7.0) × 10 −16 yr −1 (1σ uncertainty).
2007
We report the most sensitive tests to date of the assumption of local position invariance (LPI) underlying general relativity, based on a 7 yr comparison of cesium and hydrogen atomic clocks (frequency standards). The latest results place an upper limit that is over 20 times smaller than the previous most sensitive tests; this is consistent with the null shift predicted by LPI. The result is based on precise comparisons of frequencies of four hydrogen masers maintained by NIST, with four independent Cs fountain clocks-one at NIST and three in Europe-as the Sun's gravitational potential at Earth's surface varies due to Earth's orbital eccentricity.
Recent atomic clock comparisons at NIST
The European Physical Journal Special Topics, 2008
The record of atomic clock frequency comparisons at NIST over the past half-decade provides one of the tightest constraints of any present-day temporal variations of the fundamental constants. Notably, the 6-year record of increasingly precise measurements of the absolute frequency of the Hg + single-ion optical clock (using the cesium primary frequency standard NIST-F1) constrains the temporal variation of the fine structure constant α to less than 2 · 10 −16 yr −1 and offers a Local Position Invariance test in the framework of General Relativity. The most recent measurement of the frequency ratio of the Al + and Hg + optical clocks is reported with a fractional frequency uncertainty of ±5.2 · 10 −17 . The record of such measurements over the last year sensitively tests for a temporal variation of α and constrainsα/α = (−1.6 ± 2.3) · 10 −17 yr −1 , consistent with zero.
Cold Atom Clocks, Precision Oscillators and Fundamental Tests
Lecture Notes in Physics, 2004
We describe two experimental tests of the Equivalence Principle that are based on frequency measurements between precision oscillators and/or highly accurate atomic frequency standards. Based on comparisons between the hyperfine frequencies of 87 Rb and 133 Cs in atomic fountains, the first experiment constrains the stability of fundamental constants. The second experiment is based on a comparison between a cryogenic sapphire oscillator and a hydrogen maser. It tests Local Lorentz Invariance. In both cases, we report recent results which improve significantly over previous experiments.
New Limits on Coupling of Fundamental Constants to Gravity Using Sr87 Optical Lattice Clocks
Physical Review Letters, 2008
The 1 S 0 -3 P 0 clock transition frequency Sr in neutral 87 Sr has been measured relative to the Cs standard by three independent laboratories in Boulder, Paris, and Tokyo over the last three years. The agreement on the 1 10 ÿ15 level makes Sr the best agreed-upon optical atomic frequency. We combine periodic variations in the 87 Sr clock frequency with 199 Hg and H-maser data to test local position invariance by obtaining the strongest limits to date on gravitational-coupling coefficients for the fine-structure constant , electron-proton mass ratio , and light quark mass. Furthermore, after 199 Hg , 171 Yb , and H, we add 87 Sr as the fourth optical atomic clock species to enhance constraints on yearly drifts of and .
Cancellation of the Collisional Frequency Shift in Caesium Fountain Clocks
Physical Review Letters, 2007
We have observed that the collisional frequency shift in primary caesium fountain clocks varies with the clock state population composition and, in particular, is zero for a given fraction of the |F = 4, m F = 0〉 atoms, depending on the initial cloud parameters. We present a theoretical model explaining our observations. The possibility of the collisional shift cancellation implies an improvement in the performance of caesium fountain standards and a simplification in their operation. Our results also have implications for test operation of fountains at multiple π/2 pulse areas.
Physical Review D, 2010
The cryogenic sapphire oscillator (CSO) at the Paris Observatory has been continuously compared to various Hydrogen Masers since 2001. The early data sets were used to test Local Lorentz Invariance in the Robertson-Mansouri-Sexl (RMS) framework by searching for sidereal modulations with respect to the Cosmic Microwave Background, and represent the best Kennedy-Thorndike experiment to date. In this work we present continuous operation over a period of greater than six years from September 2002 to December 2008 and present a more precise way to analyse the data by searching the time derivative of the comparison frequency. Due to the long-term operation we are able to search both sidereal and annual modulations. The results gives P KT = β RMSα RMS -1 = -1.7(4.0)×10 -8 for the sidereal and -23(10)×10 -8 for the annual term, with a weighted mean of -4.8(3.7)x10 -8 , a factor of 8 better than previous. Also, we analyse the data with respect to a change in gravitational potential for both diurnal and annual variations. The result gives β H-Maserβ CSO = -2.7(1.4)×10 -4 for the annual and -6.9(4.0)×10 -4 for the diurnal terms, with a weighted mean of -3.2(1.3)×10 -4 . This result is two orders of magnitude better than other tests that use electromagnetic resonators. With respect to fundamental constants a limit can be provided on the variation with ambient gravitational potential and boost of a combination of the fine structure constant (α), the normalized quark mass (m q ), and the electron to proton mass ratio (m e /m p ), setting the first limit on boost dependence of order 10 -10 .
Predictions for laser-cooled Rb clocks
Physical Review A, 1997
Using information from a recent 85 Rb two-color photoassociation experiment, we evaluate the merits of fountain clocks based on 87 Rb and 85 Rb isotopes as alternatives to 133 Cs and find that they offer significant advantages. In the case of 87 Rb the collisionally induced fractional frequency shift is 15 times smaller than for 133 Cs. This small shift is associated with a small difference in the triplet and singlet scattering lengths for 87 Rb. For 85 Rb, the shift produced by the two m f ϭ0 clock states may have opposite signs allowing the shift to be eliminated by controlling the relative populations of these states. We also present collision quantities relevant to atomic fountain clocks containing multiply launched groups of atoms, and for evaporative cooling of 85 Rb atoms. ͓S1050-2947͑97͒50312-X͔