Turquoise Magic Wavelength of the ⁸⁷Sr Clock Transition

Optical lattice clocks of fermionic strontium offer a versatile platform for probing fundamental physics and developing quantum technologies. The bivalent electronic structure of strontium gives rise to a doubly-forbidden atomic transition that is accessible due to hyperfine mixing in fermionic strontium-87, thus resulting in a sub-millihertz natural linewidth. Currently, the most accurate optical lattice clocks operate on this narrow transition by tightly trapping strontium-87 atoms in a { magic} optical lattice at 813~nm. { Magic} wavelengths occur where the Stark shifts of both the ground and excited states are equivalent, thus eliminating any position and intensity-dependent broadening of the corresponding transition. Theoretical calculations of the electronic structure of strontium-87 have also predicted another { magic} wavelength of the clock transition at 497.01(57)~nm. In this work, we experimentally measure the novel { magic} wavelength to be $497.4363(3)$~nm. Compared to the 813~nm { magic} wavelength, 497~nm is closer to the strong 461~nm dipolar transition of strontium, resulting in larger atomic polarizability by an order of magnitude, providing deeper traps with less optical power. The proximity to the 461~transition also leads to an enhanced sensitivity of 334(10)~Hz/(nm\,ER) at the { magic} wavelength.