Investigating the 4D3/2|3,±2) - 4D5/2|3,±2) transition in Nb4+ for a THz atomic clock

In this work, the 4D3/2|3,±2)→4D5/2|3,±2) transition in the Nb4+ ion is identified as a promising candidate for a terahertz (THz) atomic clock, with the transition frequency occurring at 56.022 4 THz. This transition is primarily driven by the magnetic dipole decay channel, which can easily be accessed by a laser. We focus on the stable Nb93 isotope, which has 100% natural abundance and a nuclear spin of I=9/2 for experimental advantage. Our data analysis allows us to estimate potential systematic shifts in the proposed clock system, including those due to blackbody radiation, electric quadrupole, second-order Zeeman, and second-order Doppler shifts. The scheme presented in this study can help suppress the ac Stark and electric quadrupole shifts in the clock-frequency measurement. All these analyses suggest that the proposed THz atomic clock using Nb4+ could be valuable in both quantum thermometry and frequency metrology.