In this paper we present an experiment performed with an atomic beam spin echo
interferometer, in which massive intraparticle entanglement is demonstrated. In the
longitudinal Stern-Gerlach arrangement the nuclear spin and linear momentum of
3He particles are inextricably linked, such that the overall system state
cannot be written as the tensor product of the corresponding Hilbert spaces. The measured
data show maximal entanglement between ℋI
and ℋp. This hybrid system of one quantum and one classical
degree of freedom is a textbook example of entanglement between discrete and continuous
observables
