Towards an improved measurement of the 8 eV Thorium-229 nuclear isomer transition energy using a superconducting detector

The presence of a low-lying metastable state (^229mTh) at 8 eV [1] above the nuclear ground state in Thorium-229 provides an opportunity to construct a nuclear clock by leveraging state-of-the-art AMO physics techniques, which is expected to be more accurate than the 10^-19-level accuracy of the current best atomic clocks [2]. This nuclear clock will further enable studies of physics beyond the Standard Model, as this clock transition is predicted to exhibit enhanced sensitivity to time-variation of the Electromagnetic and Strong interaction coupling constants. However, the 0.17 eV (2%) uncertainty in the knowledge of the transition-energy [3] severely precludes direct excitation of this weak transition using spectrally narrow radiation sources. Here, we present an ongoing effort towards directly measuring the de-excitation energy of ^229mTh using a superconducting nanowire single photon detector. Our target uncertainty of 0.01 eV or better will pave the way for a direct excitation of the nuclear transition, eventually leading to a nuclear clock.

References:

[1] L. v.d. Wense et al., Nature 533, 47-51 (2016).

[2] S. M. Brewer et al., Phys. Rev. Lett. 123, 033201 (2019).

[3] B. Seiferle et al., Nature 573, 243-246 (2019); T. Sikorsky et al., Phys. Rev. Lett. 125, 142503 (2020).