High-efficiency manipulations of triply entangled states in neutron polarimetry

Abstract

Entanglement occupies a peculiar position in quantum mechanics (QM). It occurs in quantum systems that consist of space-like separated parts or-more generally-in systems whose observables belong to disjoint Hilbert spaces. The latter is the case with single-neutron systems. Here, we report on a neutron polarimetric experiment, where a triply entangled Greenberger-Horne-Zeilinger state is exploited. The entanglement of spin, momentum and total energy degree of freedom is generated utilizing a suitable combination of radio-frequency and static magnetic fields. An average deviation of expectation values from theory-ideal circumstances-of 0.016(1) confirms the predictions of QM with high accuracy, demonstrating the high-efficiency manipulation of the entangled single-neutron system.

Multifold paths of neutrons in the three-beam interferometer detected by a tiny energy kick

“…The wave functions in each path in the IFM can be written in the form of spin-path wave functions with a respective phase shift as Ψ i = e iχi s + ⊗ ψ i (i = I, II, R, I + II). Between the second and the third plate of the IFM, the paths, taken by neutrons in the IFM, are marked by slightly shifting the energy of neutrons; the neutrons' energy serves as which-way (WW) markers [13] for paths I, II, and R. In our experiment, WW-markings are achieved by the use of resonancefrequency spin-rotators (SR) [33][34][35]. The magnitude of the energy shift ∆E = ω is adjusted by the frequency ω of the oscillating magnetic-field of the corresponding SR.…”

Proving the generation of genuine multipartite entanglement in a single-neutron interferometer experiment

“…Entanglement purely between degrees of freedom in a single quantum system is extensively studied by using neutron optical techniques in particular neutron interferometry [17]: starting with a demonstration of the violation of a Bell-like inequality [18], the implementation of a triply entangled Greenberger-Zeilinger-Horne (GHZ)-like state is reported [19]. Quite recently, a test of an alternative model of quantum mechanicsá la Leggett [20] as well as high-efficiency manipulations of a tripartite-entangled system [21] are reported by using another strategy, namely, neutron polarimetry. It is worth noting here that these neutron optical techniques exploit matter-waves and are very suitable to study properties of multipartite entangled systems of matter-waves: the efficiency of manipulating degrees of freedom in a single neutron is rather high, which enabled tests of alternative models of quantum mechanics with matter-waves.…”

Error-Disturbance Uncertainty Relations in Neutron-Spin Measurements

“…The experiment was carried out at the polarimeter beam line of the tangential beam port of the research reactor facility TRIGA Mark II at the Atominstitut, Vienna University of Technology, where mainly fundamental aspects of quantum mechanics are investigated [22][23][24][25] For = 0, the error ( ) vanishes and the disturbance ( ) is maximal. The disturbance ( ) vanishes for = ( = /2) and reaches a second maximum for = − .…”