  The coupling of a qubit to a macroscopic reservoir plays a fundamental role
in understanding the complex transition from the quantum to the classical
world. Considering a harmonic environment, we use both intuitive arguments and
numerical many-body quantum tomography to study the structure of the complete
wavefunction arising in the strong-coupling regime, reached for intense
qubit-environment interaction. The resulting strongly-correlated many-body
ground state is built from quantum superpositions of adiabatic (polaron-like)
and non-adiabatic (antipolaron-like) contributions from the bath of quantum
oscillators. The emerging Schr\"odinger cat environmental wavefunctions can be
described quantitatively via simple variational coherent states. In contrast to
qubit-environment entanglement, we show that non-classicality and entanglement
among the modes in the reservoir are crucial for the stabilization of qubit
superpositions in regimes where standard theories predict an effectively
classical spin.
