  We present Spitzer observations of thirteen z~6 quasars using the Infrared
Array Camera (IRAC) and Multiband Imaging Photometer for Spitzer (MIPS). All
the quasars except SDSS J000552.34-000655.8 (SDSS J0005-0006) were detected
with high S/N in the four IRAC channels and the MIPS 24um band, while SDSS
J0005-0006 was marginally detected in the IRAC 8.0um band, and not detected in
the MIPS 24um band. We find that most of these quasars have prominent emission
from hot dust as evidenced by the observed 24um fluxes. Their spectral energy
distributions (SEDs) are similar to those of low-redshift quasars at rest-frame
0.15-3.5 um, suggesting that accretion disks and hot-dust structures for these
sources already have reached maturity. However, SDSS J0005-0006 has an unusual
SED that lies significantly below low-redshift SED templates at rest-frame 1
and 3.5 um, and thus shows a strong near-IR (NIR) deficit and no hot-dust
emission. Type I quasars with extremely small NIR-to-optical flux ratios like
SDSS J0005-0006 are not found in low-redshift quasar samples, indicating that
SDSS J0005-0006 has different dust properties at high redshift. We combine the
Spitzer observations with X-ray, UV/optical, mm/submm and radio observations to
determine bolometric luminosities for all the quasars. We find that the four
quasars with central black-hole mass measurements have Eddington ratios of
order unity.
