  Stimulated Raman adiabatic passage (STIRAP) offers significant advantages for
coherent population transfer between un- or weakly-coupled states and has the
potential of realizing efficient quantum gate, qubit entanglement, and quantum
information transfer. Here we report on the realization of STIRAP in a
superconducting phase qutrit - a ladder-type system in which the ground state
population is coherently transferred to the second-excited state via the dark
state subspace. The result agrees well with the numerical simulation of the
master equation, which further demonstrates that with the state-of-the-art
superconducting qutrits the transfer efficiency readily exceeds $99\%$ while
keeping the population in the first-excited state below $1\%$. We show that
population transfer via STIRAP is significantly more robust against variations
of the experimental parameters compared to that via the conventional resonant
$\pi$ pulse method. Our work opens up a new venue for exploring STIRAP for
quantum information processing using the superconducting artificial atoms.
