Is macroscopic quantum coherence incompatible with macroscopic realism?

The proposal by Leggett and Leggett et al. (Suppl. Prog. Theor. Phys., 69 (1980) 80;Directions in Condensed Matter Physics, edited by G. Grinstein and G. Mazenko (World Scientific, Singapore) 1986, p. 189;Jpn. J. Appl. Phys., 26 (1987) 1986, Suppl. 26-3;Phys. Rev. Lett., 54 (1985) 857) of using Macroscopic Quantum Coherence (MQC) in a SQUID as a test of the validity of Quantum Mechanics (QM) for macroscopic systems is considered. We note that if only Macroscopic Realism (MR) is assumed but the requirement that the flux measurement is non-invasive (NIM) is dropped, only the measurement of the charge would discriminate between QM and MR. This discrimination, however, depends critically on the experimental parameters. There is a region in which QM is consistent with MR, but the measurement is invasive as in QM. In this region the system is not fully macroscopic because the uncertainty relation between the flux and the conjugated charge is of the order of h. © 1995 Società Italiana di Fisica.