Coherent excitation of a $\hat{I}¼$Hz scale optical magnetic quadrupole transition

Abstract

We report on the coherent excitation of the ultranarrow ${}^1{\mathrm{S}}_0$-${}^3{\mathrm{P}}_2$ magnetic quadrupole transition in ${}^{88}\mathrm{Sr}$. By confining atoms in a state insensitive optical lattice, we achieve excitation fractions of 97(1)% and observe linewidths as narrow as 58(1) Hz. With Ramsey spectroscopy, we find coherence times of 14(1) ms, which can be extended to 266(36) ms using a spin-echo sequence. We determine the linewidth of the M2 transition to 24(7) $\hat{I}¼$Hz, confirming longstanding theoretical predictions. These results establish an additional clock transition in strontium and pave the way for applications of the metastable ${}^3{\mathrm{P}}_2$ state in quantum computing and quantum simulations.

6 pages, 4 figures, 5 pages supplemental material