Measurement of the parity violating 6S-7S transition amplitude in cesium achieved within 2 imes 10^{-13} atomic-unit accuracy by stimulated-emission detection

摘要

We exploit the process of asymmetry amplification by stimulated emissionwhich provides an original method for parity violation (PV) measurements in ahighly forbidden atomic transition. The method involves measurements of achiral, transient, optical gain of a cesium vapor on the 7S-6P_{3/2}transition, probed after it is excited by an intense, linearly polarized,collinear laser, tuned to resonance for one hyperfine line of the forbidden6S-7S transition in a longitudinal electric field. We report here a 3.5 foldincrease, of the one-second-measurement sensitivity, and subsequent reductionby a factor of 3.5 of the statistical accuracy compared with our previousresult [J. Gu\'ena et al., Phys. Rev. Lett. 90, 143001 (2003)]. Decisiveimprovements to the set-up include an increased repetition rate, betterextinction of the probe beam at the end of the probe pulse and, for the firsttime to our knowledge, the following: a polarization-tilt magnifier,quasi-suppression of beam reflections at the cell windows, and a Cs cell withelectrically conductive windows. We also present real-time tests of systematiceffects, consistency checks on the data, as well as a 1% accurate measurementof the electric field seen by the atoms, from atomic signals. PV measurementsperformed in seven different vapor cells agree within the statistical error.Our present result is compatible with the more precise Boulder result withinour present relative statistical accuracy of 2.6%, corresponding to a 2 \times10^{-13} atomic-unit uncertainty in E_1^{pv}. Theoretical motivations forfurther measurements are emphasized and we give a brief overview of a recentproposal that would allow the uncertainty to be reduced to the 0.1% level bycreating conditions where asymmetry amplification is much greater.