Decoherence of macroscopic objects from relativistic effect

We study how the decoherence of macroscopic objects originates intrinsically from the relativistic effect. With the degree of freedom of the center of mass (CM) characterizing the collective quantum state of a macroscopic object (MO), it is found that an MO consisting of N particles can decohere with a time scale of no more than √N^-1. Here, the special relativity can induce the coupling of the collective motion mode and the relative motion modes in an order of 1/c², which intrinsically results in the above minimum decoherence.