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Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS)

/sup 199/Hg/sup +/ optical frequency standard: progress report

Robert J. Rafac, Brent C. Young, Flávio C. Cruz, James A. Beall, Jonas Bergquist, Wayne M. Itano, David J. Wineland

Published Jan 22, 2003• 2 citations
Publisher

Abstract

We are developing an optical frequency standard based on the narrow /sup 2/S/sub 1/2/-/sup 2/D/sub 5/2/ electric-quadrupole transition of a single trapped /sup 199/Hg/sup +/ ion. Small linear traps designed to operate at liquid helium temperatures have been constructed which will provide confinement in the Lamb-Dicke regime for the optical transition. Cryogenic operation yields long ion storage times and significantly suppresses frequency shifts due to collisions and blackbody radiation. A major step toward the completion of this standard has been the construction and evaluation of a well isolated, high-finesse, Fabry-Perot cavity to stabilize the frequency of the interrogating laser. We report our cavity results and progress toward locking the laser frequency to the transition in the stored ion.

DOI
10.1109/freq.1999.841396

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We are developing an optical frequency standard based on the narrow /sup 2/S/sub 1/2/-/sup 2/D/sub 5/2/ electric-quadrupole transition of a single trapped /sup 199/Hg/sup +/ ion. Small linear traps designed to operate at liquid helium temperatures have been constructed which will provide confinement in the Lamb-Dicke regime for the optical transition. Cryogenic operation yields long ion storage times and significantly suppresses frequency shifts due to collisions and blackbody radiation. A major step toward the completion of this standard has been the construction and evaluation of a well isolated, high-finesse, Fabry-Perot cavity to stabilize the frequency of the interrogating laser. We report our cavity results and progress toward locking the laser frequency to the transition in the stored ion.
A cryogenic linear rf trap has been constructed to study the accuracy of a clock based on laser cooled /sup 199/Hg/sup +/. Crystals of tens of ions have been observed. The residual micromotion of the ions has been minimized and Ramsey interrogation periods of 25 s have been demonstrated for the 40.5 GHz transition. This system should eventually provide a frequency standard of high precision and accuracy. We report on the development of compact, efficient, solid-state sources at 194 nm and 282 nm for laser cooling of /sup 199/Hg/sup +/ and investigation of the /sup 2/S/sub 1/2//spl rarr//sup 2/D/sub 5/2/ quadrupole transition of interest for an optical frequency standard.
Experimental research toward the realization of an optical frequency standard of high accuracy is briefly reviewed. The studies concentrated on single, laser-cooled ions since they offer several attractive features for the achievement of high accuracy. These features include long storage time which eliminates transit-time broadening, confinement that is nearly nonperturbative to the internal level structure of the ion, laser-cooling that reduces motional shifts to small values, and electron-shelving whereby transitions to long-lived states can be detected with unit probability. The authors studied spectroscopically the electric-quadrupole allowed transition at 282 nm in a single, laser-cooled /sup 199/Hg/sup +/ ion stored in an RF Paul trap with extremely high resolution. The measured linewidth is limited by the spectral purity of the laser to about 80 Hz. Possible improvements and future directions are discussed.>
We report on work directed toward the systematic evaluation of an optical frequency standard based on the /sup 2/S/sub 1/2/-/sup 2/D/sub 5/2/ transition of a single, laser-cooled, trapped /sup 199/Hg/sup +/ ion, whose resonance frequency is 1.06/spl times/10/sup 15/ Hz. For the purpose of the evaluation, a second /sup 199/Hg/sup +/ standard has been constructed. In the cooling-laser system built for the second standard, an injection-locking scheme has been applied to a CW Ti-sapphire laser. We also report optical frequency measurements of the clock transition performed over the past 21 months with the first standard. During this term, the variation of the clock transition frequency is found to be less than /spl plusmn/1/spl times/10/sup -14/.
We describe experimental investigations of an optical frequency standard based on a single laser-cooled /sup 171/Yb/sup +/ ion confined in a radiofrequency Paul trap. The electric quadrupole transition from the /sup 2/S/sub 1/2 /(F=0) ground state to the /sup 2/D/sub 3/2/(F=2) state at 435.5 nm is used as the reference transition. The transition was resolved with a Fourier-limited width of approximately 30 Hz. In order to investigate the instability and accuracy of a future frequency standard based on the reference transition, a first experiment was done comparing two laser frequencies stabilized individually to two separate ions in different traps. As a result we found a relative frequency instability /spl sigma//sub y/(640 s)=1.5/spl middot/10/sup -15/ for the difference of the two laser frequencies. We also derived a first estimate /spl Theta/(/sup 2/D/sub 3/2/)=(3.9/spl plusmn/1.9)ea/sub 0//sup 2/ for the electric quadrupole moment of the /sup 2/D/sub 3/2/ state.