Turquoise Magic Wavelength of the ${}^{87}$Sr Clock Transition

TL;DR

This paper experimentally measures a new magic wavelength at 497.4363 nm for the ${}^{87}$Sr clock transition, enabling deeper optical traps with less power and enhanced sensitivity, advancing optical lattice clock technology.

Contribution

The study provides the first experimental confirmation of a predicted magic wavelength at 497.4363 nm for strontium-87, improving trap depth and sensitivity in optical lattice clocks.

Findings

Measured the novel magic wavelength at 497.4363 nm.

Found larger atomic polarizability at 497 nm compared to 813 nm.

Demonstrated increased sensitivity near the new magic wavelength.

Abstract

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 {\em magic} optical lattice at 813~nm. {\em 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 {\em magic} wavelength of the clock transition at 497.01(57)~nm. In this work, we experimentally measure the novel {\em magic} wavelength to be $497.4363(3)$~nm. Compared to the 813~nm {\em 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\,$E_{R}$) at the {\em magic} wavelength.