Excitation and probing of low-energy nuclear states at high-energy storage rings
Junlan Jin🇨🇳 · Hendrik Bekker🇩🇪 · Tobias Kirschbaum · Yuri A. Litvinov🇩🇪 · Adriana Pálffy🇩🇪 · Jonas Sommerfeldt · Andrey Surzhykov🇩🇪 · Peter G. Thirolf🇩🇪 · Dmitry Budker🇩🇪
Th with a low-lying nuclear isomeric state is an essential candidate for a nuclear clock as well as many other applications. Laser excitation of the isomeric state has been a long-standing goal. With relativistic Th ions in storage rings, high-power lasers with wavelengths in the visible range or longer can be used to achieve high excitation rates of Th isomers. This can be realized through direct resonant excitation, or excitation via an intermediate nuclear or electronic state, facilitated by the tunability of both the laser-beam and ion-bunch parameters. Unique opportunities are offered by highly charged Th ions due to the nuclear-state mixing. The significantly reduced isomeric-state lifetime corresponds to a much higher excitation rate for direct resonant excitation. Importantly, we propose electric dipole transitions changing both the electronic and nuclear states that are opened by the nuclear hyperfine mixing. We suggest using them for efficient isomer excitation in Li-like Th ions, via stimulated Raman adiabatic passage or single-laser excitation. We also propose schemes for probing the isomers, utilizing nuclear radiative decay or laser spectroscopy on electronic transitions, through which the isomeric-state energy can be determined with an orders-of-magnitude higher precision than the current value. The schemes proposed here for Th could also be adapted to low-energy nuclear states in other nuclei, such as Pa.