Atomic parity violation has been observed in the 6s 2 1 S0 → 5d6s 3 D1 408-nm forbidden transition of ytterbium. The parity-violating amplitude is found to be two orders of magnitude larger than in cesium, where the most precise experiments to date have been performed. This is in accordance with theoretical predictions and constitutes the largest atomic parity-violating amplitude yet observed. This also opens the way to future measurements of neutron skins and anapole moments by comparing parity-violating amplitudes for various isotopes and hyperfine components of the transition. has not yet been possible to test an important prediction of the SM concerning the variation of Q W along a chain of isotopes. It has been suggested [4] that rare-earth atoms may be good candidates for APV experiments because they have chains of stable isotopes, and the APV effects may be enhanced due to the proximity of opposite-parity levels. While the accuracy of atomic calculations is unlikely to ever approach that achieved for atoms with a single valence electron, ratios of PV-amplitudes between different isotopes should provide ratios of weak charges, without involving, to first approximation, any atomic-structure calculations.The present experiment is inspired by the prediction [5] supported by further theoretical work of [6,7], that the PV-amplitude in the chosen transition is ≈100 times larger than that in Cs. The motivation for PVexperiments in Yb is probing low-energy nuclear physics by comparing PV-effects on either a chain of naturally occurring Yb isotopes, or in different hyperfine components for the same odd-neutron-number isotope. The ratio of PV amplitudes for two isotopes of the same element is sensitive to the neutron distributions within the nucleus. The difference between PV amplitudes measured on two different hyperfine lines belonging to the same transition is a manifestation of nuclear-spin-dependent APV, which is sensitive to the nuclear anapole moments (see, for example, reviews [8,9]) that arise from weak interactions between the nucleons. As the precision of the experiment increases, a sensitive test of the Standard Model may also become possible [10].Here we report on experimental verification of the predicted PV-amplitude enhancement in Yb using a measurement of the APV amplitude for 174 Yb. The idea of the experiment is to excite the forbidden 408-nm transition ( Fig. 1) with resonant laser light in the presence of a quasi-static electric field. The PVamplitude of this transition arises due to PV-mixing of the 5d6s 3 D 1 and 6s6p 1 P 1 states. The purpose of the electric field is to provide a reference transition amplitude due to Stark-mixing of the same states, interfering with the PV amplitude. In such interference method [11,12], one is measuring the part of the transition probability that is linear in both the reference Stark-induced amplitude and the PV amplitude. In addition to enhancing the PV-dependent signal, employing the Stark-PV interference technique provides for all-important reversals allow...

We present a detailed description of the observation of parity violation in the 1 S 0 -3 D 1 408-nm forbidden transition of ytterbium, a brief report of which appeared earlier. Linearly polarized 408-nm light interacts with Yb atoms in crossed E and B fields. The probability of the 408-nm transition contains a parity-violating term, proportional to (E · B)[(E × E) · B], arising from interference between the parity-violating amplitude and the Stark amplitude due to the E field (E is the electric field of the light). The transition probability is detected by measuring the population of the 3 P 0 state, to which 65% of the atoms excited to the 3 D 1 state spontaneously decay. The population of the 3 P 0 state is determined by resonantly exciting the atoms with 649-nm light to the 6s7s 3 S 1 state and collecting the fluorescence resulting from its decay. Systematic corrections due to E-field and B-field imperfections are determined in auxiliary experiments. The statistical uncertainty is dominated by parasitic frequency excursions of the 408-nm excitation light due to the imperfect stabilization of the optical reference with respect to the atomic resonance. The present uncertainties are 9% statistical and 8% systematic. Methods of improving the accuracy for future experiments are discussed.

We present a measurement of the dynamic scalar and tensor polarizabilities of the excited state |5d6s 3 D 1 in atomic ytterbium. The polarizabilities were measured by analyzing the spectral lineshape of the 408-nm 6s 2 1 S 0 → 5d6s 3 D 1 transition driven by a standing wave of resonant light in the presence of static electric and magnetic fields. Due to the interaction of atoms with the standing wave, the lineshape has a characteristic polarizability-dependent distortion. A theoretical model was used to simulate the lineshape and determine a combination of the polarizabilities of the ground and excited states by fitting the model to experimental data. This combination was measured with a 13% uncertainty, only 3% of which was due to uncertainty in the simulation and fitting procedure. By comparing two different combinations of polarizabilities, the scalar and tensor polarizabilities of the state |5d6s 3 D 1 were measured to be α 0 ( 3 D 1 ) = 0.009(21) Hz(V/cm) −2 and α 2 ( 3 D 1 ) = −0.103(26) Hz(V/cm) −2 , respectively. We show that this technique can be applied to similar atomic systems.

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