Large Momentum Transfer Clock Atom Interferometry on the 689 nm Intercombination Line of Strontium.

We report the first realization of large momentum transfer (LMT) clock atom interferometry. Using single-photon interactions on the strontium ${}^1S_0 - {}^3P_1$ transition, we demonstrate Mach-Zehnder interferometers with state-of-the-art momentum separation of up to $141\,\hbar k$ and gradiometers of up to $81\,\hbar k$. Moreover, we circumvent excited state decay limitations and extend the gradiometer duration to 50 times the excited state lifetime. Due to the broad velocity acceptance of the interferometry pulses, all experiments are performed with laser-cooled atoms at a temperature of $3\,\mu \text{K}$. This work has applications in high-precision inertial sensing and paves the way for LMT-enhanced clock atom interferometry in gravitational wave detection and dark matter search proposals.