  The fast growth of supermassive black holes and their feedback to the host
galaxies play an important role in regulating the evolution of galaxies,
especially in the early Universe. However, due to cosmological dimming and the
limited angular resolution of most observations, it is difficult to resolve the
feedback from the active galactic nuclei (AGN) to their host galaxies.
Gravitational lensing, for its magnification, provides a powerful tool to
spatially differentiate emission originated from AGN and host galaxy at high
redshifts. Here we report a discovery of a radio lobe in a strongly lensed
starburst quasar, H1413+117 or Cloverleaf at redshift $z= 2.56$, based on
observational data at optical, sub-millimetre, and radio wavelengths. With both
parametric and non-parametric lens models and with reconstructed images on the
source plane, we find a differentially lensed, kpc scaled, single-sided radio
lobe, located at ${\sim}1.2\,\mathrm{kpc}$ to the north west of the host galaxy
on the source plane. From the spectral energy distribution in radio bands, we
find that the radio lobe has an energy turning point residing between 1.5 GHz
and 8 GHz, indicating an age of 20--50 Myr. This could indicate a feedback
switching of Cloverleaf quasar from the jet mode to the quasar mode.
