  We experimentally study a vacuum-induced Autler-Townes doublet in a
superconducting three-level artificial atom strongly coupled to a coplanar
waveguide resonator and simultaneously to a transmission line. The
Autler-Townes splitting is observed in the reflection spectrum from the
three-level atom in a transition between the ground state and the second
excited state when the transition between the two excited states is resonant
with a resonator. By applying a driving field to the resonator, we observe a
change in the regime of the Autler-Townes splitting from quantum
(vacuum-induced) to classical (with many resonator photons). Furthermore, we
show that the reflection of propagating microwaves in a transmission line could
be controlled by different frequency single photons in a resonator.
