  We report the first lattice quantum chromodynamics (QCD) study of
deuteron($np$)-like dibaryons with heavy quark flavours. These include
particles with following dibaryon structures and valence quark contents:
$\Sigma_c\Xi_{cc} (uucucc)$, $\Omega_c\Omega_{cc} (sscscc)$, $\Sigma_b\Xi_{bb}
(uububb)$, $\Omega_b\Omega_{bb} (ssbsbb)$ and $\Omega_{ccb}\Omega_{cbb}
(ccbcbb)$, and with spin ($J$)-parity ($P$), $J^{P} \equiv 1^{+}$. Using a
state-of-the art lattice QCD calculation, after controlling relevant systematic
errors, we unambiguously find that the ground state masses of dibaryons
$\Omega_c\Omega_{cc} (sscscc)$, $\Omega_b\Omega_{bb} (ssbsbb)$ and
$\Omega_{ccb}\Omega_{cbb} (ccbcbb)$ are below their respective two-baryon
thresholds, suggesting the presence of bound states which are stable under
strong and electromagnetic interactions. We also predict their masses
precisely. For dibaryons $\Sigma_c\Xi_{cc} (uucucc)$, and $\Sigma_b\Xi_{bb}
(uububb)$, we could not reach to a definitive conclusion about the presence of
any bound state due to large systematics associated with these states. We also
find that the binding of these dibaryons becomes stronger as they become
heavier in mass. This study also opens up the possibility of the existence of
many other exotic nuclei, which can be formed through the fusion of heavy
baryons, similar to the formation of nuclei of elements in the Periodic Table.
