Experimental determination of the E2-M1 polarizability of the strontium clock transition

Abstract

To operate an optical lattice clock at a fractional uncertainty below 10-17, one must typically consider not only electric-dipole (E1) interaction between an atom and the lattice light field when characterizing the resulting lattice light shift of the clock transition but also higher-order multipole contributions, such as electric-quadrupole (E2) and magnetic-dipole (M1) interactions. However, strongly incompatible values have been reported for the E2-M1 polarizability difference of the clock states (5s5p)3P0 and (5s2)1S0 of strontium [Ushijima, Phys. Rev. Lett. 121, 263202 (2018)0031-900710.1103/PhysRevLett.121.263202; Porsev, Phys. Rev. Lett. 120, 063204 (2018)0031-900710.1103/PhysRevLett.120.063204; Wu, Phys. Rev. A 100, 042514 (2019)2469-992610.1103/PhysRevA.100.042514]. This largely precludes operating strontium clocks with uncertainties of a few 10-18, as the resulting lattice light shift corrections deviate by up to 1×10-17 from each other at typical trap depths. We have measured the E2-M1 light shift coefficient using our Sr87 lattice clock and find a value of Δαqm=-987-223+174μHz. This result is in very good agreement with the value reported by Ushijima et al. [Phys. Rev. Lett. 121, 263202 (2018)0031-900710.1103/PhysRevLett.121.263202].