  Supermassive black holes (SMBHs) are the central engines of luminous quasars
and are found in most massive galaxies today. But the recent discoveries of
ULAS J1120+0641, a $2 \times 10^9$ M$_{\odot}$ BH at $z =$ 7.1, and ULAS
J1342+0928, a $8.0 \times 10^{8}$ M$_{\odot}$ BH at $z =$ 7.5, now push the era
of quasar formation up to just 690 Myr after the Big Bang. Here we report new
cosmological simulations of SMBHs with X-rays fully coupled to primordial
chemistry and hydrodynamics that show that J1120 and J1342 can form from direct
collapse black holes (DCBHs) if their growth is fed by cold, dense accretion
streams, like those thought to fuel rapid star formation in some galaxies at
later epochs. Our models reproduce all of the observed properties of J1120: its
mass, luminosity, and H II region as well as star formation rates and
metallicities in its host galaxy. They also reproduce the dynamical mass of the
innermost 1.5 kpc of its emission region recently measured by ALMA and J-band
magnitudes that are in good agreement with those found by the VISTA Hemisphere
Survey.
