Tripartite entanglement in single-neutron interferometer experiments

Abstract

We present experimental evidence of the generation of distinct types of genuine multipartite entanglement between the spin, energy, and path degrees of freedom within single-neutron quantum systems. This is achieved via the development of new spin manipulation apparatuses for neutron interferometry and the entanglement is detected via appropriately designed and optimized non-linear witnesses. We demonstrate the extraordinarily high controllability and fidelity of the generated entangled states.

Improvement of the polarized neutron interferometer setup demonstrating violation of a Bell-like inequality

“…Such setups were used for spinsuperposition, geometric phase and entanglement measurements [5,13,15]. For earlier Bell-measurement using single-neutron interferometry two different setups were realized [11,12]. In both setups the spin manipulation in the interferometer (IFM) was problematic: The contrast and the degree of polarisation were reduced.…”

“…The Mu-metal foil considerably reduced the contrast of the IFM due to dephasing. To overcome this problem another setup was designed, which does not need any material in the neutron beam in the IFM [12], shown in figure 1b). In one path of the IFM the beam passes a tube of Mu-metal which reduces the strength of the magnetic guide field and thereby induces a relative spin rotation by different Larmor precession in the two IFM paths.…”

“…Ever since neutron optical experiments, based on interference of matter waves, have provided a power full means of demonstrating effects related to fundamental aspects of quantum physics [2], such as measuring the 4π-periodicity of fermions [3], gravitational effects on the neutron [4], spin superposition [5,6] and topological phases [7,8,9]. Entanglement between different degrees of freedom like the neutron's spin, energy and path have been accomplished [10] and used for testing Bell's inequality [11,12] or measuring the influence of geometric phases [13]. Such entanglement is achieved within single particles.…”

“…In the first experiment [11] a Mu-metal sheet was used as a spin turner, which induced dephasing due to small angle scattering and thereby reduced the interference contrast. The next setup [12] solved the problem of dephasing but the degree of polarisation became problematic.…”