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 interferometerswith state-of-the-art momentum separation of up to $141\,\hbar k$ and gradiometersof up to $81\,\hbar k$. Moreover, we circumvent excited state decay limitations and extend the gradiometerduration to 50 times the excited state lifetime. Due to the broad velocity acceptance of the interferometrypulses, all experiments are performed with laser-cooledatoms 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 interferometryin gravitational wave detection and dark matter search proposals.