We describe a new test for possible variations of the fine structure constant n by comparisons of rates between clocks based on hyperfine transitions in alkali atoms with different atomic number Z. H-maser, Cs, and Hg+ clocks have a different dependence on n via relativistic contributions of order (Za)~R. ecent H-maser vs Hg+ clock comparison data improve laboratory limits on a time variation by 100-fold to give a/n~3.7 X 10 '4/yr. Future laser cooled clocks (Be+, Rb, Cs, Hg+, etc. ), when compared, will yield the most sensitive of all tests for n/n. PACS numbers: 06.20.Jr, 12.20.Fr, 31.30.Jr Since Dirac's large number hypothesis (LNH) [1], the search for a time variation of the fundamental constants has been the subject of much work [2]. Dirac noticed that the ratio of the electrostatic to gravitational forces between an electron and proton (-2 X 10'9) was close to the age of the Universe expressed in units of the light transit time across the classical electron radius, R, /c = e~/m, c3. He conjectured that these two very large quantities were proportional, hence, the ratio e~/Gm"m, would vary with the age of the Universe. A fractional change BG/G = -5 X 10 "/yr would result assuming a universe 2 X 10'o yr old. Teller and co-workers [2,3] have postulated a relationship for the fine structure constant u ' -ln(hc/Gm2), where (hc/Gm2)'I2 -(electron Compton wavelength)/(Planck length). Taken with the Dirac hypothesis of a time varying G, o. may vary Ba/a -a(BG/G) -3.6 X 10 '3/yr. Variation of the nongravitational constants is forbidden in general relativity and other metric theories of gravity, where gravitational fields are described as a geometrical property of space-time. The equiva1ence principle forms the basis for all metric theories and requires local position invariance: In local freely falling frames the outcome of any local nongravitational test experiment is independent of where and when in the Universe it is performed[4]. A changing fine structure constant n, as predicted in some cosmological string theories [5], would violate the equivalence principle signaling the breakdown of gravitation as a geometrical phenomenon and, as we show in this paper, would lead to a drift in the relative frequencies of H masers, Rb, Cs, Hg+, etc. clocks. Several analyses of paleontological, geophysical, and astronomical data were made apparently ruling out the LNH variation [2] though there have been confiicting claims for a measured variation of the gravitational constant [6]. The paleontological arguments were based upon the realization that even a small departure of the gravitational constant G from the present day value woUld make the Earth inhospitable to life. Arguments of this sort have arisen largely as a response to Dirac's LNH and have led to the development of the anthropic cosmological principle (ACP). Accordingly [7], the large number ratio (LNR) values are not a consequence of the above proportionality postulated by Dirac but rather, the present day LNR values are one of a relatively small subset (of all pos...

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The first frequency standard based on laser-cooled atoms is reported. Beryllium atomic ions were stored in a Penning trap and cooled by radiation pressure from a laser. The frequency of the 9 Be + (M It Mj) = ( -y, + y) <-• ( -y, + y) ground-state hyperfine transition at its magneticfield-independent point was determined to be 303 016 377.265 070(57) Hz. The accuracy of a frequency standard referenced to this transition was comparable to the best frequency standards, which are based on cesium atomic beams.

We have designed and built a nwel linear ion trap which permits storage of a large number of ions with reduced susceptibility to the second order Doppler effect caused by the BF conjbing fields. This new trap should store about 20 times the number of ions as a conventional RF trap with no corresponding increase in second order Doppler shift from the confining fleld. Other comparisons to etandard RF ion traps will be made.