Experimental Test of Entropic Noise-Disturbance Uncertainty Relations for Three-Outcome Qubit Measurements

Information-theoretic uncertainty relations formulate the joint immeasurability of two non-commuting observables in terms of information entropies. The trade-off of the accuracy in the outcome of two successive measurements manifests in entropic noise-disturbance uncertainty relations. Recent theoretical analysis predicts that projective measurements are not optimal, with respect to the noise-disturbance trade-offs. Therefore the results in our previous letter [PRL 115, 030401 (2015)] are outperformed by general quantum measurements. Here, we experimentally test a tight information-theoretic measurement uncertainty relation for three-outcome positive-operator valued measures (POVM), using neutron spin-1/2 qubits. The obtained results violate the lower bound for projective measurements as theoretically predicted.Comment: 14 pages, 14 figure

Spin - Rotation Coupling Observed in Neutron Interferometry

Einstein's theory of general relativity and quantum theory form the two major pillars of modern physics. However, certain inertial properties of a particle's intrinsic spin are inconspicuous while the inertial properties of mass are well known. Here, by performing a neutron interferometric experiment, we observe phase shifts arising as a consequence of the spin's coupling with the angular velocity of a rotating magnetic field. The resulting phase shifts linearly depend on the frequency of the rotation of the magnetic field. Our results agree well with the predictions derived from the Pauli - Schr\"odinger equation

Neutron optical test of completeness of quantum root-mean-square errors

One of the major problems in quantum physics has been to generalize the classical root-mean-square error to quantum measurements to obtain an error measure satisfying both soundness (to vanish for any accurate measurements) and completeness (to vanish only for accurate measurements). A noise-operator based error measure has been commonly used for this purpose, but it has turned out incomplete. Recently, Ozawa proposed a new definition for a noise-operator based error measure to be both sound and complete. Here, we present a neutron optical demonstration for the completeness of the new error measure for both projective (or sharp) as well as generalized (or unsharp) measurements.Comment: 7 pages, 4 figures and Supplementary Informatio

Three-Path Quantum Cheshire Cat Observed in Neutron Interferometry

The paradoxical phenomenon of the quantum Cheshire Cat (qCC) refers to situations where different properties of a particle appear to be localised in different paths of an interferometer and therefore spatially separated. This observation is obtained by implementing a pre- and postselection procedure. The localisations are determined qualitatively through conspicuous changes induced by weak interactions. Previous demonstrations of the qCC only used the path and spin/polarisation degrees of freedom. In addition, the present experiment uses the neutron's energy as a third property in a three-path interferometer. It is demonstrated that the three properties of neutrons are found separated in different paths in the interferometer; a detailed analysis suggests that the appearance of a property is strongly related to the geometrical relation between the state vectors of pre- and postselection with weak interactions in between. If a weak interaction in a path locally generates a state vector with a component parallel to the reference state in another path, a conspicuous intensity oscillation is expected and observed. Therefore, the appearance of the observed intensity oscillations is attributed solely to the cross-terms between the reference and the newly generated state via weak interactions

Dissecting the Shared Genetic Architecture of Suicide Attempt, Psychiatric Disorders, and Known Risk Factors

Background Suicide is a leading cause of death worldwide, and nonfatal suicide attempts, which occur far more frequently, are a major source of disability and social and economic burden. Both have substantial genetic etiology, which is partially shared and partially distinct from that of related psychiatric disorders. Methods We conducted a genome-wide association study (GWAS) of 29,782 suicide attempt (SA) cases and 519,961 controls in the International Suicide Genetics Consortium (ISGC). The GWAS of SA was conditioned on psychiatric disorders using GWAS summary statistics via multitrait-based conditional and joint analysis, to remove genetic effects on SA mediated by psychiatric disorders. We investigated the shared and divergent genetic architectures of SA, psychiatric disorders, and other known risk factors. Results Two loci reached genome-wide significance for SA: the major histocompatibility complex and an intergenic locus on chromosome 7, the latter of which remained associated with SA after conditioning on psychiatric disorders and replicated in an independent cohort from the Million Veteran Program. This locus has been implicated in risk-taking behavior, smoking, and insomnia. SA showed strong genetic correlation with psychiatric disorders, particularly major depression, and also with smoking, pain, risk-taking behavior, sleep disturbances, lower educational attainment, reproductive traits, lower socioeconomic status, and poorer general health. After conditioning on psychiatric disorders, the genetic correlations between SA and psychiatric disorders decreased, whereas those with nonpsychiatric traits remained largely unchanged. Conclusions Our results identify a risk locus that contributes more strongly to SA than other phenotypes and suggest a shared underlying biology between SA and known risk factors that is not mediated by psychiatric disorders.Peer reviewe

Development and perfomance of a miniaturised spin rotator suitable for neutron interferometer experiments

A miniaturised versatile spin rotator for application in neutron interferometer experiments is developed. The coil design without material in the beam path allows for a magnetic field adjustable to an arbitrary direction perpendicular to the neutron beam. The field simulations show a homogeneous field over the beam cross-section of 8 mm x 5 mm and a field transition less than or similar to 20 mm from inside to outside. The performance of the fabricated miniaturised coil was quantified by carrying out the polarimeter experiment of Demirel et al (New I. Phys., 17:023065, 2015) regarding spin-rotation coupling. The high efficiency spin manipulations by the implemented rotating magnetic field results in a linear dependence between the phase shift and the rotation frequency. In near future, the spin rotator will be used to investigate spin-rotation coupling in a related interferometer experiment

Experimental test of tight state-independent preparation uncertainty relations for qubits

The well-known Robertson-Schrodinger uncertainty relations miss an irreducible lower bound. This is widely attributed to the lower bound's state dependence. Therefore, Abbott et al. introduced a general approach to derive tight state-independent uncertainty relations for qubit measurements [Mathematics 4, 8 (2016)]. The relations are expressed in two measures of uncertainty, which are standard deviation and entropy, both functions of the expectation value. Here, we present a neutron polarimetric test of the tight state-independent preparation uncertainty relations for orthogonal, as well as nonorthogonal, Pauli spin observables. The final results, obtained with pure and mixed spin states, reproduce the theoretical predictions clearly for arbitrary initial states of variable degree of polarization