Precision Measurement of M1 Optical Clock Transition in Ni^(12+)

Highly charged ions (HCIs) are of particular interest in new physics searches and quantum metrology. As one of the most competitive candidates, Ni^(12+) was selected as one of the next generation of optical atomic clocks with two forbidden transitions M1 and E2 in the visible spectral range. Here, we perform high-precision wavelength measurement of the M1 transition using the Shanghai-Wuhan Electron Beam Ion Trap (SW-EBIT). We improved the calibration scheme of the spectra and used auxiliary Ar^+ lines for calibration and correction. Compared to our previous results, the final accuracy is improved by a factor of 5, reaching the sub-pm level.