Laser spectroscopy of trapped Ra+ ions: towards a single-ion optical clock

PhD ceremony: Mr. O.O. Versolato, 16.15 uur, Aula Academiegebouw, Broerstraat 5, Groningen

Dissertation: Laser spectroscopy of trapped Ra+ ions: towards a single-ion optical clock

Promotor(s): prof. K. Jungmann, prof. R.G.E. Timmermans

Faculty: Mathematics and Natural Sciences

A single trapped and laser-cooled radium ion, Ra⁺, is a promising candidate for high precision experiments, such as on atomic parity violation (APV) and atomic clocks. APV experiments provide a stringent test of the Standard Model of particles physics with high sensitivity for physics beyond. Ultra-narrow transitions in Ra⁺can be employed for optical frequency standards, or “clocks”. As an important step towards such experiments excited-state laser spectroscopy was performed on short-lived trapped^209-214Ra⁺ions produced from the AGOR cyclotron at KVI. Hyperfine structure constants of Ra⁺atomic states and isotope shifts of relevant transitions were studied, providing benchmarks for the required atomic theory at percent level accuracy. The measurement of a lower limit of the lifetime of the meta-stable 6d²D_5/2state provides an important confirmation of the fundamental availability of long coherence times in the trapped Ra⁺system, required for high-quality clocks. The potential of the electric quadrupole transitions 7s²S_1/2-6d²D_3/2,6d²D_5/2in Ra⁺isotopes as single-ion optical frequency standards was explored. The frequency shifts of the clock transitions due to external fields and corresponding uncertainties were calculated. Several competitive candidates have been identified. In particular, the transition 7s²S_1/2(F=2,m_F=0)-6d²D_3/2(F=0,m_F=0) in²²³Ra⁺at 828nm wavelength stands out because of the absence of linear Zeeman and electric quadrupole shifts. It could be exploited as a compact, robust, and low-cost atomic clock operating at a fractional frequency uncertainty of 10^-17. With more experimental effort, the^223,225,226Ra⁺clocks could be pushed to a projected performance reaching even the 10^-18level.