  We explore ground-state entanglement properties of helium atom confined at
the center of an impenetrable spherical cavity of varying radius by using
explicitly correlated Hylleraas-type basis set. Results for the dependencies of
the von Neumann and linear entanglement entropic measures on the cavity radius
are discussed in details. Some highly accurate numerical results for the von
Neumann and linear entropy are reported for the first time. It is found that
the transition to the strong confinement regime is manifested by the entropies
as an appearance of the inflection points on their variations.
