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

3D printed magnets for neutron spin manipulation

Devices for manipulation of the neutron spin are vital for experiments in neutron optics such as neutron interferometry. Here we introduce a new type of such devices which are based on a magnetic material that can be 3D printed in complex shapes. We have constructed a spin flipper wherein the angle of spin rotation can be adjusted by variation of the distance between magnetized pieces. As the device does not contain any heat dissipating coils we expect interferometric measurements to become more stable and hence more accurate. Results of an experiment using polarized neutrons verify the device's functionality, and indicate the potential of the new method. A second experiment for demonstration of the 4π spinor symmetry of fermionic wave functions is in progress.

Experimental Demonstration of Direct Path State Characterization by Strongly Measuring Weak Values in a Matter-Wave Interferometer

A method was recently proposed and experimentally realized for characterizing a quantum state by directly measuring its complex probability amplitudes in a particular basis using so-called weak values. Recently, Vallone and Dequal [Phys. Rev. Lett. 116, 040502 (2016)PRLTAO0031-900710.1103/PhysRevLett.116.040502] showed theoretically that weak measurements are not a necessary condition to determine the weak value. Here, we report a measurement scheme used in a matter-wave interferometric experiment in which the neutron path system's quantum state was characterized via direct measurements, using both strong and weak interactions. Experimental evidence is given that strong interactions outperform weak ones for tomographic accuracy. Our results are not limited to neutron interferometry, but can be used in a wide range of quantum systems.

Classical Physics and the Bounds of Quantum Correlations

A unifying principle explaining the numerical bounds of quantum correlations remains elusive, despite the efforts devoted to identifying it. Here, we show that these bounds are indeed not exclusive to quantum theory: for any abstract correlation scenario with compatible measurements, models based on classical waves produce probability distributions indistinguishable from those of quantum theory and, therefore, share the same bounds. We demonstrate this finding by implementing classical microwaves that propagate along meter-size transmission-line circuits and reproduce the probabilities of three emblematic quantum experiments. Our results show that the "quantum" bounds would also occur in a classical universe without quanta. The implications of this observation are discussed.