Search for Variations of Fundamental Constants using Atomic Fountain Clocks

Abstract

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).The same limit applies to a possible variation of the quantity (µ Rb /µCs)α −0.44 , which involves the ratio of nuclear magnetic moments and the fine structure constant.PACS numbers: 06.30. Ft, 32.80.Pj, 06.20.Jr Since Dirac's 1937 formulation of his large number hypothesis aiming at tying together the fundamental constants of physics [1], large amount of work has been devoted to test if these constants were indeed constant over time [2,3].In General Relativity and in all metric theories of gravitation, variations with time and space of non gravitational fundamental constants such as the fine structure constant α = e 2 /4πǫ 0 c are forbidden. They would violate Einstein's Equivalence Principle (EEP). EEP imposes the Local Position Invariance stating that in a local freely falling reference frame, the result of any local non gravitational experiment is independent of where and when it is performed. On the other hand, almost all modern theories aiming at unifying gravitation with the three other fundamental interactions predict violation of EEP at levels which are within reach of near-future experiments [4,5]. As the internal energies of atoms or molecules depend on electromagnetic, as well as strong and weak interactions, comparing the frequency of electronic transitions, fine structure transitions and hyperfine transitions as a function of time or gravitational potential provides an interesting test of the validity of EEP.To date, very stringent tests exist on geological and cosmological timescales. The analysis of the Oklo nuclear reactor showed that, 2 × 10 9 years ago, α did not differ from the present value by more than 10 −7 of its value [6]. Light emitted by distant quasars has been used to perform absorption spectroscopy of interstellar clouds. For instance, measurements of the wavelengths of molecular hydrogen transitions test a possible variation of the electron to proton mass ratio m e /m p [7]. Comparisons between the gross structure and the fine structure of neutral atoms and ions would indicate that α for a redshift z ∼ 1.5 (∼ 10 Gyr) differed from the present value: ∆α/α = (−7.2 ± 1.8) × 10 −6 [8]. Today this is the only claim that fundamental constants might change.On much shorter timescales, several tests using frequency standards have been performed [9,10,11]. These laboratory tests have a very high sensitivity to changes in fundamental constants. They are repeatable, systematic errors can be tracked as experimental conditions can be changed.In this letter we present results that place a new stringent limit to the time variation of fundamental constants. By comparing the hyperfine energies of 13...

Variation of the fine-structure constant: an update of statistical analyses with recent data

“…numbers (Prestage et al 1995;Sortais et al 2001;Marion et al 2003;Bize et al 2003;Fischer et al 2004;Peik et al 2004). The astronomical methods are based mainly on the analysis of highredshift quasar absorption systems.…”

Time variation of the fine structure constant and of the Higgs vacuum expectation value on cosmological time scales

“…Several observations can establish limits to the variation of different fundamental constants, such as the atomic clocks (Bize et al 2003;Fischer et al 2004;Peik et al 2004;Prestage et al 1995;Sortais et al 2000;Marion et al 2003), the Oklo natural fission reactor (Damour & Dyson 1996;Fujii et al 2000) and the analysis of the spectra of quasar absorption systems. These astronomical observations suggest a possible variation of the fine structure constant and the electron-to-proton mass ratio (Webb et al 1999(Webb et al , 2001Murphy et al 2001aMurphy et al ,b, 2003Ivanchik et al 2005;Reinhold et al 2006;Tzanavaris et al 2007).…”

Laser sources for precision spectroscopy on atomic strontium

“…Proposals based on different interrogation schemes have been put forward (optical lattice clock [6], engineered atom clock [7,8]) suggesting the possibility to reach the 10 −17 level of overall accuracy. Indeed, thanks to the higher oscillator frequency, a clock in the optical domain could potentially reach a stability level of 10 −18 at 1 s [6] which represents a factor of 10 4 improvement with respect to the best microwave standards [9]. A clock with such stability and accuracy could be used as a powerful test for relativistic theory, searching for deviation of fine structure constant and to define a new atomic time standard.…”