  Quantum orbital selective Mott (OSM) transitions are investigated within
dynamical mean-field theory based on a two-orbital Hubbard model with different
bandwidth at half filling. We find two distinct OSM phases both showing
coexistence of itinerant electrons and localized spins, dependent on whether
the Hund's coupling is full or of Ising type. The critical values and the
nature of the OSM transitions are efficiently determined by entanglement
entropy. We reveal that vanishing of the Kondo energy scale evidenced by
absence of local spin fluctuations at low frequency in local dynamical spin
susceptibility is responsible for the appearance of non-Fermi-liquid OSM phase
in Ising Hund's coupling case. We argue that this scenario can also be applied
to account for emergent quantum non-Fermi liquid in one-band Hubbard model when
short-range antiferromagnetic order is considered.
