@phdthesis{13650,
  author = {Alexander Aeppli},
  title = {Clock with 8 x 10^{-19} systematic uncertainty},
  abstract = {<p>Optical atomic clocks have revolutionized time keeping, leading to the most accurate and precise measurements that humankind has ever made. The work in this thesis builds upon years<br>of progress to construct the most accurate clock to date. Strontium atoms are trapped in a one dimensional (1D) optical lattice formed within an in-vacuum build up cavity oriented along gravity.<br>We probe the ultra-narrow, environmentally insensitive 5s<sup>2</sup> <sup>1</sup>S<sub>0</sub> --&gt; 5s5p <sup>3</sup>P<sub>0</sub> electronic transition with a laser based upon a single-crystal silicon resonator. To build the best atomic clock, we need<br>precise quantum control of the atoms as well as comprehensive stabilization of systematic shifts. We discuss how in-situ imaging allows us to measure frequency gradients within an atomic sample,<br>including determining the gravitation redshift over less than a millimeter [22]. Through precision spectroscopy, we characterize the motional states of the atoms. In a tilted 1D optical lattice, atoms<br>occupy Wannier-Stark external wavefunctions. Tuning the wavefunction using a “magic depth,” we realize a density shift cancellation, allowing us to operate with 10<sup>5</sup> atoms with a negligible density<br>shift [1]. Under strong interactions, an dynamical phase transition appears during a Rabi drive. We understand and tame the lattice light shift through a comprehensive campaign modulating the lattice<br>depth, frequency, and external wavefunction [70]. We reduce the uncertainty in the largest systematic shift in room temperature Sr clocks, the black body radiation shift, by remeasuring the atomic<br>response function and carefully determining the radiant temperature [2]. Other systematic shifts have much smaller uncertainties, and all together we achieve a systematic uncertainty of 8.1 x 10<sup>-19</sup><br>in fractional frequency units–the lowest of any clock to date [2]. Lastly, we discuss recent work to push the strontium clock into new regimes. We reduce both the laser and atomic instability, mapping<br>out the coherence limitations of both systems. We can combine atom interferometry techniques with optical clock techniques to realize a system that combines classical and relativistic geodesy tools. Ongoing frequency comparisons with optical clocks at NIST allow us to test the veracity of our systematic uncertainty, perhaps aiding in the redefinition of the SI second.</p>},
  year = {2025},
  journal = {JILA and Department of Physics},
  volume = {PhD},
  pages = {202},
  month = {2025/07},
  publisher = {University of Colorado Boulder},
  address = {Boulder},
}