Research project B02 – SFB 1227 DQ-mat – Leibniz University Hannover

Introduction

Supported by their ever-improving precision, optical clocks have been employed over the past two decades to perform some of the most stringent tests of fundamental physical principles. Following this idea, the goal of this project is to employ high-performance optical clocks to search for violations of the predictions of the standard model of particle physics, commonly referred to as new-physics effects.

Results

Towards this goal, we have tested local position invariance (LPI) by repeatedly comparing the output of atomic clocks realizing different clock transition frequencies. The different sensitivities of the involved atomic states to fundamental constants, such as the fine-structure constant α or the proton-to-electron mass ratio μ, allows us to either identify the corresponding violating constant or to constrain its instability. Within DQ-mat, we have recently established the most stringent bounds on temporal variations and a potential coupling to gravity for α and μ. These investigations profited in particular from the high sensitivity of the clock transitions of the Yb⁺ ion to variations of α.

To perform reliable tests and to further push the limits of our searches for new-physics effects, we have improved the understanding of frequency shifts resulting from blackbody radiation and the lattice laser light for the Sr clock, which aided to resolve a discrepancy between experimentally and theoretically determined atomic parameters and lead to a better understanding of the atomic structure of Sr. We have started to operate a Yb⁺ ion clock setup in which ⁸⁸Sr⁺ can be employed as ancillary ion, e.g., to measure the perturbing thermal radiation. The latter investigation has also helped to resolve a serious tension in recent measurements of the ⁸⁸Sr⁺ clock transition frequency.

Both systems, the ⁸⁷Sr lattice clock and the ¹⁷¹Yb⁺ ion clock, have also been employed in long-term frequency comparisons and to search for another new-physics curiosity: dark matter.

Objectives

For the third funding period, we plan to further exploit the large sensitivity of our clocks in searches for new-physics effects. Following approaches also pursued in B03 (multi-ion spectroscopy) and collaborating with A09 (designed states and measurements) and B10 (ultralight dark matter) will help us to increase the resolvable particle mass in searches for a coupling of dark matter to normal matter. By continuing to improve the performance of the clocks and to compare them, we are confident to be well-positioned to resolve or further constrain new-physics effects.

Publications

First 1 2

Dörscher S, Huntemann N, Schwarz R, Lange R, Benkler E, Lipphardt B et al. Optical frequency ratio of a ¹⁷¹Yb⁺ single-ion clock and a ⁸⁷Sr lattice clock. METROLOGIA. 2021 Feb;58(1):015005. doi: 10.1088/1681-7575/abc86f

Lange R, Huntemann N, Rahm JM, Sanner C, Shao H, Lipphardt B et al. Improved Limits for Violations of Local Position Invariance from Atomic Clock Comparisons. Physical review letters. 2021 Jan 6;126(1):011102. doi: 10.1103/PhysRevLett.126.011102

Lisdat C, Dörscher S, Nosske I, Sterr U. Blackbody radiation shift in strontium lattice clocks revisited. Physical Review Research. 2021 Dec 9;3(4):L042036. doi: 10.1103/physrevresearch.3.l042036

Dörscher S, Al-Masoudi A, Bober M, Schwarz R, Hobson R, Sterr U et al. Dynamical decoupling of laser phase noise in compound atomic clocks. Communications Physics. 2020 Dec 1;3(1):185. doi: 10.1038/s42005-020-00452-9

Roberts BM, Delva P, Al-Masoudi A, Amy-Klein A, Bærentsen C, Baynham CFA et al. Search for transient variations of the fine structure constant and dark matter using fiber-linked optical atomic clocks. New journal of physics. 2020 Sept;22(9):093010. doi: 10.1088/1367-2630/abaace

Schulte M, Lisdat C, Schmidt PO, Sterr U, Hammerer K. Prospects and challenges for squeezing-enhanced optical atomic clocks. Nature Communications. 2020 Nov 24;11(1):5955. doi: 10.1038/s41467-020-19403-7

Schwarz R, Dörscher S, Al-Masoudi A, Benkler E, Legero T, Sterr U et al. Long term measurement of the Sr 87 clock frequency at the limit of primary Cs clocks. Physical Review Research. 2020 Aug;2(3):033242. doi: 10.1103/PhysRevResearch.2.033242

Herbers S, Dörscher S, Benkler E, Lisdat C. Phase noise of frequency doublers in optical clock lasers. Optics express. 2019;27(16):23262-23273. doi: 10.1364/OE.27.023262

Schwarz R, Dörscher S, Al-Masoudi A, Vogt S, Li Y, Lisdat C. A compact and robust cooling laser system for an optical strontium lattice clock. Review of scientific instruments. 2019 Feb 25;90(2):023109. doi: 10.1063/1.5063552

Dörscher S, Schwarz R, Al-Masoudi A, Falke S, Sterr U, Lisdat C. Lattice-induced photon scattering in an optical lattice clock. Physical Review A. 2018 Jun 25;97(6):063419. doi: 10.1103/PhysRevA.97.063419

Mehlstäubler TE, Grosche G, Lisdat C, Schmidt PO, Denker H. Atomic clocks for geodesy. Reports on Progress in Physics. 2018 Jun;81(6):064401. Epub 2018 Apr 18. doi: 10.48550/arXiv.1803.01585, 10.1088/1361-6633/aab409

Origlia S, Pramod MS, Schiller S, Singh Y, Bongs K, Schwarz R et al. Towards an optical clock for space: Compact, high-performance optical lattice clock based on bosonic atoms. Physical Review A. 2018 Nov 29;98(5):053443. doi: 10.1103/PhysRevA.98.053443

Delva P, Lodewyck J, Bilicki S, Bookjans E, Vallet G, Le Targat R et al. Test of Special Relativity Using a Fiber Network of Optical Clocks. Physical review letters. 2017 Jun 2;118(22):221102. doi: 10.1103/PhysRevLett.118.221102

Pachomow E, Dahlke VP, Tiemann E, Riehle F, Sterr U. Ground-state properties of Ca₂ from narrow-line two-color photoassociation. Physical Review A. 2017 Apr 25;95(4):043422. doi: 10.48550/arXiv.1702.00710, 10.1103/PhysRevA.95.043422

All publications of the Collaborative Research Centre

Overview