  The present work reports on an extended research endeavor focused on the
theoretical and experimental realization of a macroscopic quantum superposition
(MQS) made up with photons. As it is well known, this intriguing, fundamental
quantum condition is at the core of a famous argument conceived by Erwin
Schroedinger, back in 1935. The main experimental challenge to the actual
realization of this object resides generally on the unavoidable and
uncontrolled interactions with the environment, i.e. the decoherence leading to
the cancellation of any evidence of the quantum features associated with the
macroscopic system. The present scheme is based on a nonlinear process, the
"quantum injected optical parametric amplification", that maps by a linearized
cloning process the quantum coherence of a single - particle state, i.e. a
Micro - qubit, into a Macro - qubit, consisting in a large number M of photons
in quantum superposition. Since the adopted scheme was found resilient to
decoherence, the MQS\ demonstration was carried out experimentally at room
temperature with $M\geq $ $10^{4}$. This result elicited an extended study on
quantum cloning, quantum amplification and quantum decoherence. The related
theory is outlined in the article where several experiments are reviewed such
as the test on the "no-signaling theorem" and the dynamical interaction of the
photon MQS with a Bose-Einstein condensate. In addition, the consideration of
the Micro - Macro entanglement regime is extended into the Macro - Macro
condition. The MQS interference patterns for large M were revealed in the
experiment and the bipartite Micro-Macro entanglement was also demonstrated for
a limited number of generated particles: $M\precsim 12$. At last, the
perspectives opened by this new method are considered in the view of further
studies on quantum foundations and quantum measurement.
