The accuracy of state-of-the-art atomic clocks is derived from the insensitivity of narrow optical atomic resonances to environmental perturbations. Two such resonances in singly ionized lutetium have been identified with potentially lower sensitivities compared to other clock candidates. Here we report measurement of the most significant unknown atomic property of both transitions, the static differential scalar polarizability. From this, the fractional blackbody radiation shift for one of the transitions is found to be −1.36(9) × 10−18 at 300 K, the lowest of any established optical atomic clock. In consideration of leading systematic effects common to all ion clocks, both transitions compare favorably to the most accurate ion-based clocks reported to date. This work firmly establishes Lu+ as a promising candidate for a future generation of more accurate optical atomic clocks.
We examine a range of effects arising from ac magnetic fields in high precision metrology. These results are directly relevant to high precision measurements, and accuracy assessments for state-ofthe-art optical clocks. Strategies to characterize these effects are discussed and a simple technique to accurately determine trap-induced ac magnetic fields in a linear Paul trap is demonstrated using 171 Yb + .
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]
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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 ...
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.
We measure the differential polarizability of the 176 Lu + 1 S0 ↔ 3 D1 clock transition at multiple wavelengths. This experimentally characterizes the differential dynamic polarizability for frequencies up to 372 THz and allows an experimental determination of the dynamic correction to the blackbody radiation shift for the clock transition. In addition, measurements at the near resonant wavelengths of 598 and 646 nm determine the two dominant contributions to the differential dynamic polarizability below 372 THz. These additional measurements are carried out by two independent methods to verify the validity of our methodology. We also carry out a theoretical calculation of the polarizabilities using the hybrid method that combines the configuration interaction (CI) and the coupled-cluster approaches, incorporating for the first time quadratic non-linear terms and partial triple excitations in the coupled-cluster calculations. The experimental measurements of the | 3 D1||r|| 3 PJ | matrix elements provide high-precision benchmarks for this theoretical approach.
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