Spectroscopy of Trapped ¹³⁸Ba⁺ Ions for Atomic Parity Violation and Optical Clocks

Abstract

Trapped Ba + and Ra + ions offer the possibility to test the Standard Model by performing an independent high-precision determination of the Weinberg angle (sin 2 θ W) at low momentum transfer. In such a measurement of atomic parity violation, table-top experiments complement studies of weak interaction effects at high energy in the search for new physics. The singly-charged heavy alkaline earth metal ions combine high intrinsic sensitivity with tractable atomic structure owing to their single valence electron. In addition, trapped Ba + or Ra + ions can serve as reference for an optical atomic clock that is sensitive to variation of the fine structure constant α. Determining sin 2 θ W requires localizing a single laser-cooled Ba + or Ra + ion in a standing-wave light field to a fraction of an optical wavelength. High-precision atomic theory calculations are crucial for interpreting the measurements and need experimental input. We have performed preparatory spectroscopy measurements with trapped Ba + ions and investigated experimental techniques for characterizing ion traps. We have determined the optical transition frequencies between low-lying levels of 138 Ba + with laser spectroscopy referenced to an optical frequency comb. Using a lineshape model based on eight-level optical Bloch equations, we determined the 6s 2 S 1/2-5d 2 D 3/2 transition frequency to be 146 114 384.0(0.1) MHz and the 5d 2 D 3/2-6p 2 P 1/2 transition frequency to be 461 311 878.5(0.1) MHz, obtaining for the first time sub-MHz precision on these transitions. Light shifts play an important role in the measurement of sin 2 θ W and offer a way to obtain information on (ratios of) atomic transition matrix elements. We have carried out an exploratory study of the light shift in 138 Ba + caused by an off-resonant laser tuned close to the 5d 2 D 3/2-6p 2 P 1/2 transition. The observed spectra are analyzed by combining the optical lineshapes with calculated light shifts of individual Zeeman components. Atomic state lifetimes provide a benchmark for calculations of transition amplitudes. We have measured the lifetime of the long-lived 5d 2 D 5/2 level in 138 Ba + using a technique based on quantum jumps with one to four trapped ions. We have investigated known systematic effects in detail to evaluate their influence. We measured the lifetime of the 5d 2 D 5/2 level to be 26.3(0.6) s, which is about 4σ shorter than previously published experimental results. This discrepancy needs to be clarified to ensure the reliability of atomic parity violation measurements ahead. This work contributes toward a precise determination of sin 2 θ W with trapped Ba + or Ra + ions in search of physics beyond the Standard Model.

Gravitational lens time-delay as a probe of a possible time variation of the fine-structure constant

“…The Runaway Dilaton model is a particular case of scalar-tensor theories of gravity commented in Sect. 3 [37,38,53]. One can show that the Friedmann equation in this scenario is as follows…”

“…Among scenarios beyond standard model that produce a temporal variation of alpha, we can cite a particular class of string theory inspired-models, 2 the so-called runaway dilaton model [37,38]. In this scenario, the runaway of the scalar field dilaton towards strong 3 coupling may yield a temporal variation of the fine-structure constant.…”

Gravitational lens time-delay as a probe of a possible time variation of the fine-structure constant

“…On the other hand, variations in α have also been explored on Earth with atomic clock measurements [22] and isotope ratio measurements [23], where its sensitivity (around 10 −18 ) provides a useful constraint on possible time variation of α. In astronomical context, especially from white dwarfs astronomical observations, constraints with gravitational potential at the level 2.7 ± 9.1.10 −5 were obtained [24,25] with great accuracy.…”

Electric and Magnetic Field Control for Electric Dipole Moment Searches

“…custom built DAQ (Barry and Caddie)[112][113][114]. The DAQ pc records the signals, and affords remote control of the experimental configuration and live plotting of the recorded data.…”