A search for permanent electric dipole moment of ${}_{}{}^{199}{}_{}{}^{}\mathrm{Hg}$ atoms has yielded the null result d${(}^{199}$Hg)=(0.7±1.5)×${10}^{\mathrm{-}26}$ e⋅cm, which improves by an order of magnitude the limits on several possible interactions that violate time-reversal symmetry. The experiment was performed by the use of optically pumped atomic oscillators to measure any shift in the NMR frequency of ${}_{}{}^{199}{}_{}{}^{}\mathrm{Hg}$ (I=(1/2) produced by an external electric field.

• Received 17 August 1987

DOI:https://doi.org/10.1103/PhysRevLett.59.2275