  We study single-particle potential of hyperons in nuclear medium starting
from QCD. First we carry out lattice QCD numerical simulation to extract
baryon-baryon interactions from QCD by means of the HAL QCD method. We employ a
full QCD gauge configuration ensemble at almost physical point so that hadron
masses are nearly physical, e.g. pion mass is 146 MeV, kaon mass is 525 MeV,
and nucleon mass is 956 MeV. Then, with some simplifications, we apply the
obtained hyperon interactions to the Brueckner-Hartree-Fock theory and
calculate single-particle potential of hyperons in nuclear medium
$U_{Y}(\rho,k)$. For the symmetric nuclear matter at the normal nuclear matter
density, we obtain $U_{\Lambda}(\rho_0,0)=-33$ MeV, $U_{\Sigma}(\rho_0,0)=+11$
MeV, and $U_{\Xi}(\rho_0,0)=-6$ MeV. These results are qualitatively compatible
with values suggested from experiments. This success is remarkable and
encouraging because we are trying to reveal nature of baryon-baryon
interactions starting from QCD, and this agreement proves that our approach is
essentially correct.
