Title: High-Precision Frequency Comparisons and Searches for New Physics with Yb+ Optical Clocks
Authors: Lange, Richard, Physikalisch-Technische Bundesanstalt (PTB), Fachbereich 4.4, Zeit und Frequenz
Contributors: HostingInstitution: Physikalisch-Technische Bundesanstalt (PTB), ISNI: 0000 0001 2186 1887
Resource Type: Text / Dissertation
Publisher: Physikalisch-Technische Bundesanstalt (PTB)
Rights: Download for personal/private use only, if your national copyright law allows this kind of use.
Relationships: IsPartOf: ISSN 0341-6712
IsIdenticalTo: ISBN 978-3-95606-623-8
Dates: Available: 2021-12-16
Created: 2021-09
File: Download File (application/pdf) 127.29 MB (133473717 Bytes)
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Keywords optical frequency standard ; precision spectroscopy ; local Lorentz invariance ; local position invariance ; natural lifetime ; magic wavelength ; twisted light
Abstract: State-of-the-art optical atomic clocks are based on laser-cooled trapped atoms or ions featuring forbidden transitions. A laser with sub-Hertz linewidth is frequency stabilized to such a transition, which permits frequency measurements with relative systematic uncertainties in the low 10-18 range.
The performance of optical atomic clocks is continuously improved by more efficient detection and suppression of external perturbations that cause shifts of the atomic transition frequency, and by enhancing the coherent interaction between atom and laser oscillator.

In this thesis, advances of the 171Yb+ single-ion optical clocks at the national metrology institute of Germany (PTB) are reported, realizing the frequencies of both an electric quadrupole (E2) and an electric octupole (E3) transition. Two Yb+(E3) clocks are compared and an agreement within their combined fractional uncertainty of 4.2 × 10-18 is found. An analysis of the data for potential frequency oscillations improves the limits on Lorentz violating parameters for electrons by about two orders of magnitude. A long-term comparison of the E3/E2 transition frequency ratio tightens the limit on potential temporal variations of the fine structure constant α by about a factor of 20 to (1/α)(dα/dt) = 1.0(1.1) × 10-18/yr. Comparisons of an Yb+(E3) clock and two caesium fountain clocks yields νE3 = 642121496772645.10(8) Hz, the most accurate determination of an optical transition frequency to date.

Relevant atomic parameters of the E3 transition are investigated in more detail: From the transition strength and laser intensity, the excited state natural lifetime is determined as 1.58(7) years. For a characterization of the light shift of the E3 transition, the zero-crossing point of the scalar differential polarizability is measured at 681.2(5) nm, which is called a magic wavelength. Precision measurements of the electric quadrupole moments of the excited states of both the E2 and E3 transition, Θ(2D3/2) = 1.95(1)ea02 and Θ(2F7/2) = -0.0297(5)ea02, with e the elementary charge and a0 the Bohr radius, indicate the different electronic structure of the excited states and the different sensitivities of the two transitions to shifts induced by electric field gradients.

The characterization of an advanced single-ion Yb+ trap system employing gold-coated endcap electrodes is presented. A reduction of the ion motional heating rate by a factor of 25 compared to previous trap versions is obtained, facilitating longer interaction times between ion and laser. First frequency comparisons to the other Yb+ clocks at PTB yield agreements at the low 10-17 level, presumably limited by photoelectric stray fields.

Novel interrogation methods for the control or suppression of specific frequency shifts are discussed: A coherent suppression scheme for tensorial frequency shifts is introduced, relying on a rotation of the magnetic field vector during the dark time of a Ramsey sequence, and a suppression of the electric quadrupole shift by a factor of 260 is demonstrated. Autobalanced Ramsey spectroscopy is presented that provides universal immunity to frequency shifts related to aberrations of the pulses in a Ramsey sequence. Finally, excitation of an E3 transition using twisted light, i.e. with the ion placed in the dark center of a Laguerre-Gaussian beam featuring orbital angular momentum, is demonstrated for the first time, permitting a reduction of the light shift.
Series Information: PTB-Bericht Opt-93
Citation: Lange, Richard. High-Precision Frequency Comparisons and Searches for New Physics with Yb+ Optical Clocks, 2021. Physikalisch-Technische Bundesanstalt (PTB). DOI: https://doi.org/10.7795/110.20211216