Isotope shift spectroscopy of ions in cryogenically cooled neutral plasmas

This thesis describes precision measurements of isotope shifts of Nd+ ions using a novel cryogenic ion source. Isotope shift measurements are useful in searching for a hypothetical light boson that couples with electrons and neutrons, and which could be the long-sought-after dark matter particle. Isotope shifts of two transitions of the same element, scaled by a mass-dependent factor, can be plotted against each other to make a King plot. The nonlinearity of such a King plot can be used to constrain the mass of the new physics boson and its coupling strength to electrons and neutrons (denoted as yeyn). In this experiment, we take advantage of five stable spin-zero isotopes of neodymium to measure the isotope shifts of two optical transitions in Nd+ with MHz-level accuracy. The experiment employs the cryogenic ion source, which is designed to produce cold and dense neutral plasmas by laser ablation of metal targets, followed by cryogenic buffer gas cooling. In this ion source, large ion densities (≤ 109 cm-3) can be obtained at temperatures as low as 6 K. The lasers used for the isotope shift measurements were stabilized using a novel transfer interferometer laser stabilization method, which is a simple and robust way to stabilize multiple lasers with different frequencies. The King plot analysis of the Nd+ isotope shift measurements constrains yeyn ≤ 1.4×10-9, which is comparable to the constraints placed by state-of-the-art isotope shift measurements on other atomic ions. We also discuss the prospects for further improvements to the accuracy of Nd+ isotope shifts using telecom-band optical clock transitions identified in this thesis, which could probe for new physics bosons with yeyn as low as 10-15, and lead to extremely precise tests of physics beyond the standard model.

Department dc:contributor.department

Physics

Year dc:date.issued

2020

Author dc:creator

• Bhatt, Nishant

Advisor dc:contributor.advisor

• Vutha, Amar

Statement dc:rights

• Attribution-NoDerivatives 4.0 International

Licence dc:rights.uri

• http://creativecommons.org/licenses/by-nd/4.0/

Handle dc:identifier.uri

http://hdl.handle.net/1807/103481

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/103481