If I'm not mistaken: "invisible" really means it's a "symmetry-forbidden" interaction to disperse the energy stored as a qubit in the holmium atom into the platinum matrix. In physics and chemistry "forbidden" means it happens, but has a modest energy barrier to arrange second-sphere stuff in the right way so that conservation (angular momentum, probably in this case) rules aren't violated. In this case, the apparatus is chilled so the likelihood of crossing that energy barrier is low.<p>not 100% certain; chemist (not a quantum physicist) speaking here.