Measurement of the branching ratios for 6P 1/2 decays to 6S 1/2 and 5D 3/2 in 138 Ba + are reported with the decay probability from 6P 1/2 to 5D 3/2 measured to be p = 0.268177 ± (37)stat − (20)sys. This result differs from a recent report by 12σ. A detailed account of systematics is given and the likely source of the discrepancy is identified. The new value of the branching ratio is combined with a previous experimental results to give a new estimate of τ = 7.855(10) ns for the 6P 1/2 lifetime. In addition, ratios of matrix elements calculated from theory are combined with experimental results to provide improved theoretical estimates of the 6P 3/2 lifetime and the associated matrix elements. arXiv:1905.06523v1 [physics.atom-ph]

The uniformity of the intensity and phase of laser beams is crucial to high-performance atom interferometers. Inhomogeneities in the laser intensity profile cause contrast reductions and systematic effects in interferometers operated with atom sources at micro-Kelvin temperatures, and detrimental diffraction phase shifts in interferometers using large momentum transfer beam splitters. We report on the implementation of a socalled top-hat laser beam in a long-interrogation-time cold-atom interferometer to overcome the issue of the inhomogeneous laser intensity encountered when using Gaussian laser beams. We characterize the intensity and relative phase profiles of the top-hat beam and demonstrate its gain in atom-optics efficiency over a Gaussian beam, in agreement with numerical simulations. We discuss the application of top-hat beams to improve the performance of different architectures of atom interferometers.

We propose and experimentally demonstrate a scheme which effects hyperfine averaging during a Ramsey interrogation of a clock transition. The method eliminates the need to average over multiple optical transitions, reduces the sensitivity of the clock to its environment, and reduces inhomogeneous broadening in a multi-ion clock. The method is compatible with auto-balanced Ramsey spectroscopy, which facilitates elimination of residual shifts due to imperfect implementation and ac stark shifts from the optical probe. We demonstrate the scheme using correlation spectroscopy of the 1 S0 ↔ 3 D1 clock transition in a three-ion Lu + clock. From the demonstration we are able to provide a measurement of the 3 D1 quadrupole moment, Θ( 3 D1) = 0.634(9)ea 2 0 .

We demonstrate precision measurement and control of inhomogeneous broadening in a multiion clock consisting of three 176 Lu + ions. Microwave spectroscopy between hyperfine states in the 3 D1 level is used to characterise differential systematic shifts between ions, most notably those associated with the electric quadrupole moment. By appropriate alignment of the magnetic field, we demonstrate suppression of these effects to the ∼ 10 −17 level relative to the 1 S0 ↔ 3 D1 optical transition frequency. Correlation spectroscopy on the optical transition demonstrates the feasibility of a 10 s Ramsey interrogation in the three ion configuration with a corresponding projection noise limited stability of σ(τ ) = 8.2 × 10 −17 / √ τ .With fractional uncertainties near to ∼ 10 −18 , stateof-the-art optical atomic clocks are among the most accurate scientific artefacts [1]. The two most successful realizations are ensembles of neutral atoms stored in optical lattices [2,3] and ions confined in radio-frequency (RF) traps [4,5]. The latter offers strong confinement such that atoms can be reused for subsequent clock interrogation and measurement. The stability of the current generation of trapped-ion optical clocks is limited by single-ion operation. This has limited the instability of ion-based clocks to ∼ 10 −15 / √ τ , for which averaging times τ of several days or even weeks are required to reach 10 −18 resolution. Modest improvements to stability can be expected as laser technology develops to allow longer interrogation times but ideally this would go hand-in-hand with an increase in the number of ions.Within the standard quantum limit (SQL), clock stability improves with the √ N where N is the number of atoms [6]. With an ensemble of ions, frequency resolution could be further enhanced using entangled states [7][8][9][10][11] or cascaded interrogation schemes [12,13]. From a technological standpoint, extension of clock operation to a small ensemble of ions is an immediate application for devices developed for small-scale quantum information processing (QIP). However, characterizing and maintaining exquisite control over various systematic effects in an ion ensemble is a significant challenge.Multi-ion operation is complicated by electric quadrupole (EQ) shifts arising from the Coulomb fields of neighbouring ions, excess-micromotion (EMM) shifts induced by the radio-frequency (rf) trapping field, and inhomogeneous magnetic fields. Efforts and proposals towards high-accuracy multi-ion optical clocks include (i) precision engineering of the ion trap to suppress EMM shifts [14], (ii) employing clock transitions with a negative differential scalar polarisability, ∆α 0 , to eliminate EMM shifts in a large ion crystal [15,16], and (iii) using dynamic decoupling or rf-dressed states to 646 nm 1 S 0 3 D 1 3 D 2 3 P 0 = 8 = 7 = 6 847.7 nm Hyperfine splitting: ~11.2 GHz 10.5 GHz 3 P 1 1 D 2 622 nm 895 nm 350 nm FIG. 1. Relevant energy level diagram of a 176 Lu + ion showing: the 1 S0 ↔ 3 D1 clock transition at 848 nm, the 3 D1 ↔ 3 ...

We show that it is possible to change from a subnatural electromagnetically induced transparency (EIT) feature to a subnatural electromagnetically induced absorption (EIA) feature in a (degenerate) three-level Λ system. The change is effected by turning on a second control beam counter-propagating with respect to the first beam. We observe this change in the D2 line of Rb in a room temperature vapor cell. The observations are supported by density-matrix analysis of the complete sublevel structure including the effect of Doppler averaging, but can be understood qualitatively as arising due to the formation of N -type systems with the two control beams. Since many of the applications of EIT and EIA rely on the anomalous dispersion near the resonances, this introduces a new ability to control the sign of the dispersion.

Branching fractions for decays from the P 3/2 level in 138 Ba + have been measured with a single laser-cooled ion. Decay probabilities to S 1/2 , D 3/2 and D 5/2 are determined to be 0.741716(71), 0.028031(23) and 0.230253(61), respectively, which are an order of magnitude improvement over previous results. Our methodology only involves optical pumping and state detection, and is hence relatively free of systematic effects. Measurements are carried out in two different ways to check for consistency. Our analysis also includes a measurement of the D 5/2 lifetime, for which we obtain 30.14(40) s.

No abstract

No abstract