Highly Ionized Trapped 229-Thorium:A New Paradigm Towards a Nuclear Clock

Introduction

Among the more than 3000 nuclides that are naturally occurring or that have been artificially synthesized, thorium-229 is truly exceptional. Its remarkably low excitation energy makes it the ideal candidate for nuclear frequency metrology, surpassing current atomic clocks. Such a "nuclear clock" opens doors to fundamental physics, testing time-variations of constants and exploring the enigma of dark matter.

Methodology

Within HITHOR, a conceptually novel methodology towards such a clock is proposed, eventually leading to a no-electron “bare-nucleus” clock with trapped fully ionized 229Th90+ where all external perturbations from surrounding electrons are absent. Highly-ionized 229Th will be established as a distinctive laboratory for scientific explorations at the interface of atomic electrons and the nucleus.

Nuclear Hyperfine Mixing

By adding a single electron to the nucleus, the unique effect of nuclear hyperfine mixing (NHM) is unlocked. Induced by the strong magnetic field of this one electron, a vast acceleration of the nuclear decay by up to a millionfold is triggered. Hence, for one-electron 229Th89+, laser excitation of the nucleus as well as the reemission of photons are each enhanced by up to this factor of a million.

To date, laser excitation of the nucleus hasn’t been accomplished. NHM will help to overcome this obstacle and be exploited as a booster towards 229Th laser excitation and a corresponding nuclear clock.

Facilities and Collaboration

HITHOR will be realized at the ion storage and trapping facilities at GSI in Darmstadt, the only laboratory worldwide where highly ionized 229Th can be synthesized in flight, decelerated, and finally trapped at rest.

At GSI and its Helmholtz Institute Jena, I will bring together the extraordinary expertise of in-house scientists from the various disciplines required to tackle the challenges. Initial experiments will pave the path towards high-precision VUV laser spectroscopy of few- or no-electron 229Th, and ultimately towards a single-ion quantum logic nuclear clock.