  We present Spitzer IRAC imaging of the large-scale jet in the quasar PKS
1136-135 at wavelengths of 3.6 and 5.8 um, combined with previous VLA, HST, and
Chandra observations. We clearly detect infrared emission from the jet,
resulting in the most detailed multifrequency data among the jets in
lobe-dominated quasars. The spectral energy distributions of the jet knots have
significant variations along the jet, like the archetypal jet in 3C 273. The
infrared measurements with IRAC are consistent with the previous idea that the
jet has two spectral components, namely (1) the low-energy synchrotron spectrum
extending from radio to infrared, and (2) the high-energy component responsible
for the X-ray flux. The optical fluxes may be a mixture of the two components.
We consider three radiation models for the high-energy component: inverse
Compton scattering off CMB photons by radio-emitting electrons in a highly
relativistic jet, synchrotron radiation by a second distinct electron
population, and synchrotron radiation by ultra high energy protons. Each
hypothesis leads to important insights into and constraints on particle
acceleration in the jet, as well as the basic physical properties of the jet
such as bulk velocity, transporting power, and particle contents.
