  Quantum Darwinism is a compelling theory that describes the quantum-to
classical transition as the emergence of objectivity of quantum systems.
Spectrum broadcast structure and strong quantum Darwinism are two extensions of
this theory with emphasis on state structure and information respectively. The
complete experimental verification of these three frameworks, however, requires
quantum state tomography over both the system and accessible environments, thus
limiting the feasibility and scalability of experimental tests. Here, we
introduce a subspace-dependent objectivity operation and construct a witness
that detects non-objectivity by comparing the dynamics of the
system-environment state with and without the objectivity operation. We then
propose a photonic experimental simulation that implements the witnessing
scheme. Our work proposes a route to further experimental exploration of the
quantum to classical transition.
