Speaker
Description
Optical atomic clocks represent the state of the art in time and frequency metrology, achieving unprecedented levels of precision and stability by exploiting ultra-narrow optical transitions in atoms [1]. With demonstrated fractional uncertainties approaching the $10^{-18}$ level and beyond, optical clocks now surpass microwave standards and play an essential role in the redefinition of the SI second [2], as well as in precision tests of fundamental physics [3] and frequency-ratio measurements. The continued pursuit of improved clock performance has therefore driven the exploration of atomic species that offer reduced sensitivity to systematic effects. In this context, neutral mercury (Hg) optical lattice clocks have emerged as promising candidates for next-generation optical frequency standards due to their intrinsically small blackbody radiation shift and favorable atomic structure [4]. Compared to widely studied systems such as strontium and ytterbium, Hg exhibits a significantly reduced sensitivity to thermal radiation at room temperature, thereby suppressing one of the dominant systematic frequency shifts. The availability of both fermionic and bosonic isotopes further enhances the appeal of Hg for precision clock studies. In fermionic isotopes, the $^1S_{0} - {^3P_{0}}$ clock transition is enabled through a hyperfine induced electric dipole (E1) channel, whereas in bosonic isotopes, where hyperfine interactions are absent, the transition proceeds via a weak E1–M1 two-photon mechanism. These distinct excitation pathways provide complementary opportunities to investigate isotope dependent effects and to test the accuracy of relativistic many-body theories.
In this work, we present a comprehensive theoretical investigation of clock transition related properties of neutral Hg isotopes using an all-particle multireference Fock-space relativistic coupled-cluster (FSRCC) theory [5,6]. We calculate excitation energies of low-lying electronic states, electric dipole (E1) and magnetic dipole (M1) transition amplitudes, hyperfine structure reduced matrix elements, and isotope shift parameters relevant to the $^1S_{0} - ^3P_{0}$ clock transition in both fermionic and bosonic Hg isotopes. Using these atomic parameters, we compute the lifetimes of the metastable clock states and determine the ground-state static electric dipole polarizability using the perturbed relativistic coupled-cluster (PRCC) theory [7,8]. To improve the accuracy of our results further, we incorporate relativistic and quantum electrodynamical (QED) corections, along with higher-order electron correlation effects through perturbative triple excitations. Our results provide essential theoretical input for reducing systematic uncertainties and guide ongoing experiments toward the realization and improvement of neutral mercury optical lattice clocks.
References:
[1] A. D. Ludlow et al., Rev. Mod. Phys. 87, 637–701 (2015).
[2] F. Riehle, Comptes Rendus Physique 16, 506 (2015).
[3] V. A. Dzuba, V. V. Flambaum and S. Schiller, Phys. Rev. A 98, 022501 (2018).
[4] L. Yi et al., Phys. Rev. Lett. 106, 073005 (2011).
[5] B. K. Mani, S. Chattopadhyay and D. Angom, Comp. Phys. Commu. 213, 136 (2017).
[6] P. Gakkhar, Ravi Kumar, D. Angom and B. K. Mani, Phys. Rev. A 110, 013119 (2024).
[7] R. Kumar, S. Chattopadhyay, D. Angom, and B. K. Mani, Phys. Rev. A 101, 012503 (2020).
[8] R. Kumar, D. Angom, and B. K. Mani, Phys. Rev. A 106, 032801 (2022).