Isotropic Phase-Number Squeezing and Macroscopic Quantum Coherence

A new master equation performing isotropic phase-number squeezing is suggested. The phase properties of coherent superpositions are analyzed when the state evolves in presence of a bath with fluctuations squeezed in this isotropic way. We find that such a reservoir greatly improves persistence of coherence with respect to either a customary thermal bath, or to an anisotropically squeezed phase-sensitive bath.