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 100 s have been demonstrated for the 40.5 GHz transition. Systematic shifts to the clock transition due to magnetic field fluctuations as well as heating of the ions during the clock cycle have been evaluated. This system should eventually provide a frequency standard of high precision and accuracy.
A Ramsey interrogation scheme was used to measure the phase shift of laser-cooled
87Rb clock-transition pseudospins arising as a result of a reversal of a bias-magnetic field, i.e., $\mathbf{B}\ensuremath{\rightarrow}\ensuremath{-}\mathbf{B}$, during the interrogation. While no phase shift occurred when the reversal was sudden, the Ramsey fringes were shifted by a factor of $\ensuremath{\pi}$ when the reversal was adiabatic. We thus verified the prediction that the spin states
∣F,m=0⟩ acquire a purely topological and parity-dependent phase factor of $(\ensuremath{-}1{)}^{F}$ as a result of $\mathbf{B}\ensuremath{\rightarrow}\ensuremath{-}\mathbf{B}$.