Probing multiple electric-dipole-forbidden optical transitions in highly charged nickel ions

Highly charged ions (HCIs) are promising candidates for the next generation of atomic clocks, owing to their tightly bound electron cloud, which significantly suppresses common environmental disturbances quantum oscillator. Here we propose and pursue an experimental strategy that, while focusing on various HCIs a single element, keeps number candidate clock transitions as large possible. Following this strategy, identify four adjacent charge states nickel that offer many six optical transitions. Experimentally, demonstrated essential capability producing these in low-energy compact Shanghai-Wuhan Electron Beam Ion Trap. We measured wavelengths magnetic-dipole ($M$1) one electric-quadrupole ($E$2) with accuracy several ppm novel calibration method; two lines were observed characterized first time controlled laboratory settings. Compared earlier determinations, our measurements improved wavelength by order magnitude. Such crucial constraining range laser finding "needle haystack" narrow lines. In addition, calculated frequencies quality factors, evaluated sensitivity hypothetical variation electromagnetic fine structure constant $\alpha$ needed fundamental physics applications. argue all intrinsic immunity perturbations oscillators, them has projected fractional frequency uncertainty down remarkable level 10$^{-19}$.