We report the first Doppler-free measurement of the ground state energy in helium, using two-photon excitation of the 1^1\emS-2^1\emS transition. The required 120 nm radiation is generated by harmonic upconversion of a pulse-amplified cw laser. Our initial measurement, recently completed at NIST, includes determination of the frequency shift and chirp from pulsed laser amplification. The result for the ground state Lamb shift is 41104(48) MHz, in fair agreement with theory and other experiments. This approach has the potential for significantly better accuracy once various technical improvements are implemented.
[F2.02] Measurement of the Cesium Electric-Dipole Moment
Larry Hunter, Stephen Peck, Daniel Krause, Erica Newman (Amherst College)
In 1989 new limits were established on the electron edm by measuring the electric-dipole moment (edm) of atomic cesium.(S.A. Murthy, D. Krause, Jr., Z.L. Li and L.R. Hunter, Phys. Rev. Lett.63, 965 (1989).) Work on the measurement of the cesium edm has continued and a number of important improvements have been made. The current experiment uses four cells in order to subtract fluctuations in magnetic field gradients. Larger cells are used to improve the electric field homogeneity and reversibility. The cells are heated by raising the temperature of the entire magnetic shield assembly. This results in greater temperature uniformity, which reduces magnetic noise associated with thermoelectric currents. New detectors have been designed and assembled which have electronics noise well below the photon noise. These improvements have resulted in more than a factor of twenty improvement in the experiment's sensitivity. The current status of the experiment will be reviewed and the most recent data will be reported.
[F2.03] A Precise Measurement of the Muonium Ground State Hyperfine Structure Interval and the Muon Magnetic Moment
Malcolm Boshier (University of Sussex), F. G. Mariam, R. Prigl, P. A. Thompson, K. A. Woodle (BNL), M. Janousch (ETH Zürich), K. Jungmann, G. zu Putlitz, I. Reinhard (Univ. Heidelberg), O. van Dyck, C. Pillai (LANL), P. Egan (LLNL), S. Dhawan, X. Fei, M. Grosse Perdekamp, V. W. Hughes, D. Kawall, W. Liu, W. Schwarz (Yale Univ.)
Data-taking has been completed on a new high precision
experiment
at the Los Alamos Meson Physics Facility with the goal of determining the
muonium (\mu^+e^-) ground state hyperfine structure interval
to \sim 10 ppb, and the muon to proton magnetic moment ratio
to \sim 90 ppb, each corresponding to about a fourfold improvement.
The experiment uses microwave magnetic resonance
spectroscopy and improves on previous work(F. G. Mariam et al.,
Phys. Rev. Lett.)~49, 993 (1982). by using
a chopped muon beam to obtain
narrow resonance lines,(M. G. Boshier et al.,
Phys. Rev.)~A52, 1948 (1995). a higher \mu^+ beam intensity, a more homogeneous
magnetic field, and an improved muon stopping distribution measurement.
Resonance lines were recorded using both magnetic field
and microwave frequency sweeping
methods. The status of the analysis will be presented.
[F2.04] High precision tests of QED corrections in high-Z, Li-like ions
K. T. Cheng, M. H. Chen (Lawrence Livermore National Laboratory, Livermore, CA 94550), J. Sapirstein (Phys. Dept., U. of Notre Dame, Notre Dame, IN 46556)
QED corrections to transition energies are known to be significant for high-Z ions, but it is not easy to make precision tests of these data, as uncertainties in QED corrections can easily be masked by uncertainties in atomic structure calculations. With techniques like the relativistic many-body perturbation theory and the relativistic configuration-interaction method, atomic correlation energies for high-Z ions can now be calculated to very high precision. Comparing theory with recent high-resolution measurements of the spectra of Li-like Bi^80+ taken at the Livermore Electron Beam Ion Trap facility can test QED corrections to the x-ray energy of the 2s - 2p_3/2 transition to 0.1% level, an accuracy unprecedented for highly-charged, many-electron systems. In particular, our studies clearly show the importance of higher-order QED effects beyond simple screening corrections.
[F2.05] Measurement of excited state hyperfine splittings in francium
J. E. Simsarian, L. A. Orozco, G. D. Sprouse, W. Z. Zhao (Department of Physics and Astronomy SUNY Stony Brook, NY)
The 7S_1/2 \rightarrow 8S_1/2 transition in francium provides the possibility for a measurement of atomic parity nonconservation. We use cold trapped radioactive francium atoms in a magneto-optic trap at the Stony Brook superconducting LINAC. The atoms are an excellent sample for precision spectroscopy of excited hyperfine states. An atomic parity nonconservation experiment requires an ab initio calculation of an atomic matrix element for the interaction that occurs at the nucleus. The hyperfine interaction is also sensitive to the electron wave functions at small radius. Comparisons of measured hyperfine splittings with calculations are a good test of the calculated electron wave functions near the nucleus. Because francium is an alkali atom the calculations can be done with a high accuracy. We have measured the hyperfine splitting between the 8s~^2S_1/2, F=11/2 and F=13/2 of ^210Fr and compare the results to ab initio calculations. We have also measured the hyperfine splitting between the 7p~^2P_1/2, F=11/2 and F=13/2 states of ^210Fr and between the F=3 and F=4 states of ^211Fr. This work is supported by NIST and NSF.
[F2.06] Laser-Cooled Rb Fountain Clock
Chad Fertig, Kurt Gibble (Yale University, New Haven CT)
We have constructed a prototype of a laser-cooled ^87Rb fountain clock. We collect 10^10 ^87Rb atoms in a vapor cell magneto-optic trap (MOT) using a solid state laser system. A grating stabilized laser injects a separate slave laser for each of the 6 beams of the MOT. We launch the atoms by frequency shifting the 3 downward propagating laser beams and then adiabatically cool the atoms to temperatures as low as 1.85 \muK in the fountain. During the fountain trajectory, the atoms pass through 2 state preparation microwave cavities and then up and down through the high-Q TE_2,0,1 "clock" cavity. The flight region is surrounded by 2 layers of magnetic shielding and is also a tuned TM_1,1,11 cavity with which we can probe the magnetic C-field in the flight region. We will present our experimental results including measurements of the cold collision shifts for ^87Rb and discuss the potential clock performance. Calculations suggest that the shift should be 15 times smaller than that for a Cs fountain clock.( S. J. J. M. F. Kokkelmans, B. J. Verhaar, K. Gibble, and D. J. Heinzen, Phys. Rev. A. 56), 4389 (1997).^,( K. Gibble and S. Chu, Phys. Rev. Lett. 70), 1771 (1993).
[F2.07] Shifts of the Zeeman Transition Frequency in a Far-off-resonance Dipole Trap
M.V. Romalis, E.N. Fortson (University of Washington, Seattle, WA)
Possible use of ultracold trapped atoms to search for an atomic EDM has been considered for several years(M. Bijlsma, B.J. Verhaar, and D.J. Heinzen, Phys. Rev A 49), R4285 (1994); N. Davidson, H. J. Lee, C.S. Adams, M. Kasevich, and S. Chu, Phys. Rev. Lett. 74, 1311 (1995).. A suitable trap for such experiments is a far-off-resonance optical trap, which does not perturb the Zeeman transition frequency to first order. The spin relaxation rate due to Raman scattering is also negligible. We have calculated higher order effects, which can cause significant dipole and quadrupole shifts of the Zeeman levels. The dipole shift can be caused by the residual circular polarization of the trapping light. There is also a dipole shift linear in the applied static electric field(J. Hodgdon, B.R. Heckel and E.N. Fortson, Phys. Rev. A 43), 3343, (1991).. The quadrupole shift appears only if the total angular momentum is greater than 1/2. It is quadratic in the optical or static electric field. The calculations are done for Cs and Hg, as examples of atoms with and without electron spin. The shifts for Cs may present a serious difficulty, while for Hg they are 5 orders of magnitude smaller and do not appear to be serious.