  The high resilience to de-coherence shown by a recently discovered
Macroscopic Quantum Superposition (MQS) involving a number of photons in excess
of 5 x 10^4 motivates the present theoretical and numerical investigation. The
results are placed in close comparison with the properties of the well known
MQS based on |alpha> states. The very critical decoherence properties of the
latter MQS are found to be fully accounted for, in a direct a simple way, by a
unique "universal" function: indeed a new property of the quantum "coherent
states".
