Massive spin-momentum entanglement measured in an atomic beam spin echo experiment

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 ℋ _I and ℋ _p . This hybrid system of one quantum and one classical degree of freedom is a textbook example of entanglement between discrete and continuous observables.