Hertz-Level Measurement of the Optical Clock Frequency in a Single ⁸⁸ Sr ⁺ Ion

Abstract

The frequency of the 5s 2S(1/2)-4d 2D(5/2) electric quadrupole clock transition in a single, trapped, laser-cooled 88Sr+ ion has been measured by using an optical frequency comb referenced to a cesium fountain primary frequency standard. The frequency of the transition is measured as 444,779,044,095,484.6 (1.5) hertz, with a fractional uncertainty within a factor of 3 of that of the cesium standard. Improvements required to obtain a cesium-limited frequency measurement are described and are expected to lead to a 88Sr+ optical clock with stability and reproducibility exceeding that of the primary cesium standard.

Attosecond‐precision ultrafast photonics

“…By stabilizing the spacing (repetition rate, f rep ) and the offset (carrier-envelope offset frequency, f ceo ) of the frequency comb, one can measure an optical frequency with unprecedented accuracy [2,3]. Optical frequency combs produced by mode-locked lasers have enabled major advances in highprecision laser spectroscopy [4,5] and provided the clockwork for optical atomic clocks [6][7][8]. The importance of these developments has been recognized by the 2005 Nobel Prize in Physics, shared by Theodor Hänsch and John Hall for their contributions to the frequency comb technology.…”

Optical Atomic Coherence at the 1-Second Time Scale

“…Enhancing their ratio, which is equivalent to improving spectral resolving power, characterizes much of the recent progress in these fields. Trapped ions have so far provided the best platform for research along this direction, resulting in a number of seminal achievements (3)(4)(5)(6)(7)(8). The principal advantage of the ion system lies in the clean separation between the internal atomic state and the external center-of-mass motion, leading to long coherence times associated with both degrees of freedom.…”

Quantum physics exploring gravity in the outer solar system: the SAGAS project

“…Instead of the microwave frequencies used in PHARAO, the SAGAS clock uses optical frequencies. Ground based optical clocks are evolving at a significantly fast rate, with one or two single ion clocks already demonstrating instabilities ∼4 × 10 −17 at < 10 4 s and 2 × 10 −17 accuracy in realising the unperturbed ion frequency [37][38][39][40][41]. There is good reason to expect similar performance for a range of other optical clock systems, which is extendable to below the target specification at longer times.…”

“…. ) excludes a number of the above mentioned species, leaving three possibilities: 40 Ca + (729 nm), 171 Yb + quadrupole (436 nm), and 88 Sr + (674 nm). These show little difference in sensitivity to perturbing effects, essentially the effect of blackbody radiation and electric fields from the trap.…”