  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.
Because of 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 on even narrower
transitions, a key ingredient in proposals for gravitational wave detection and
dark matter searches.
