Coherent excitation of a $\mu$Hz scale optical magnetic quadrupole transition

TL;DR

This paper demonstrates the coherent excitation of an ultranarrow magnetic quadrupole transition in strontium-88, achieving extremely narrow linewidths and long coherence times, opening new avenues for quantum technologies.

Contribution

It reports the first coherent excitation of a $^{1}S_0$-$^{3}P_2$ magnetic quadrupole transition in strontium-88 with record narrow linewidths and extended coherence times.

Findings

Achieved 97% excitation fraction of the transition.

Measured linewidth as narrow as 58 Hz and transition linewidth of 24 μHz.

Extended coherence time to over 200 ms using spin-echo sequences.

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) $\mu$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.