  We present near-infrared imaging of the host galaxies of 17 quasars in the
redshift range 1 < z < 2, carried out at the ESO VLT UT1 8m telescope under
excellent seeing conditions (~0.4 arcsec). The sample includes radio-loud (RLQ)
and radio-quiet (RQQ) quasars with similar distribution of redshift and optical
luminosity. For all the observed objects but one we have derived the global
properties of the surrounding nebulosity. The host galaxies of both types of
quasars follow the expected trend in luminosity of massive ellipticals
undergoing simple passive evolution, but there is a systematic difference by a
factor ~2 in the host luminosity between RLQs and RQQs (M_K(RLQ) = -27.55 +-
0.12 and M_K(RQQ) = -26.83 +- 0.25). Comparison with quasar hosts at similar
and lower redshift indicates that the difference in the host luminosity between
RLQs and RQQs remains the same from z = 2 to the present epoch. No significant
correlation is found between the nuclear and the host luminosities. Assuming
that the host luminosity is proportional to the black hole mass, as observed in
nearby massive spheroids, these quasars emit at very different levels (spread
\~1.5dex) with respect to their Eddington luminosity and with the same
distribution for RLQs and RQQs. Apart from a factor of ~2 difference in
luminosity, the hosts of RLQs and RQQs appear to follow the same cosmic
evolution as massive inactive spheroids. Our results support a view where
nuclear activity can occur in all luminous ellipticals without producing a
significant change in their global properties and evolution. Quasar hosts
appear to be already well formed at z ~2, in disagreement with models for the
joint formation and evolution of galaxies and active nuclei based on the
hierarchical structure formation scenario.
