Nuclear clocks for testing fundamental physics

Abstract The low-energy, long-lived isomer in 229 Th, first studied the 1970s as an exotic feature nuclear physics, continues to inspire a multidisciplinary community of physicists. It has stimulated innovative ideas and studies that expand understanding atomic structure heavy elements interaction nuclei with bound electrons coherent light. Using resonance frequency, determined by strong electromagnetic interactions inside nucleus, it is possible build highly precise clock will be fundamentally different from all other clocks based on resonant frequencies electron shell. open opportunities for sensitive tests fundamental principles particularly searches violations Einstein’s equivalence principle new particles beyond standard model. been proposed use search variations coupling constants dark matter searches. Th optical still represents major challenge view tremendous gap nearly 17 orders magnitude between present uncertainty transition frequency (about 0.2 eV, corresponding ?48 THz) natural linewidth (in mHz range). Significant experimental progress achieved recent years, which briefly reviewed. Moreover, research strategy outlined consolidate our knowledge about essential 229m properties, determine laser spectroscopic precision, realize types apply them precision comparisons test physics. Two avenues discussed: laser-cooled trapped ions allow experiments complete control nucleus–electron minimal systematic shifts, Th-doped solids enabling at high particle number electronic environments.