17 research outputs found
Observation of nonadditive mixed state phases with polarized neutrons
In a neutron polarimetry experiment the mixed state relative phases between
spin eigenstates are determined from the maxima and minima of measured
intensity oscillations. We consider evolutions leading to purely geometric,
purely dynamical and combined phases. It is experimentally demonstrated that
the sum of the individually determined geometric and dynamical phases is not
equal to the associated total phase which is obtained from a single
measurement, unless the system is in a pure state.Comment: RevTex, 4 pages, 4 figures, accepted by PR
Neutron detection in the frame of spatial magnetic spin resonance
AbstractThis work is related to neutron detection in the context of the polarised neutron optics technique of spatial magnetic spin resonance. By this technique neutron beams may be tailored in their spectral distribution and temporal structure. We have performed experiments with very cold neutrons (VCN) at the high-flux research reactor of the Institut Laue Langevin (ILL) in Grenoble to demonstrate the potential of this method. A combination of spatially and temporally resolving neutron detection allowed us to characterize a prototype neutron resonator. With this detector we were able to record neutron time-of-flight spectra, assess and minimise neutron background and provide for normalisation of the spectra owing to variations in reactor power and ambient conditions at the same time
Engineering of triply entangled states in a single-neutron system
We implemented a triply entangled Greenberger-Horne-Zeilinger(GHZ)-like state
and coherently manipulated the spin, path, and energy degrees of freedom in a
single neutron system. The GHZ-like state was analyzed with an inequality
derived by Mermin: we determined the four expectation values and finally
obtained M = 2.558 +/- 0.004 > 2, which exhibits a clear violation of the
noncontextual assumption and confirms quantum contextuality.Comment: 4 pages, 2figure
MONOPOL - A traveling-wave magnetic neutron spin resonator for tailoring polarized neutron beams
We report on first experimental tests of a neutron magnetic spin resonator at a very cold neutron beam port of the high flux reactor at the ILL Grenoble. When placed between two supermirror neutron polarizers and operated in a pulsed traveling-wave mode it allows to decouple its time- and wavelength-resolution and can therefore be used simultaneously as electronically tunable monochromator and fast beam chopper. As a first ‘real’ scientific application we intend its implementation in the PERC (p roton and e lectron r adiation c hannel) project related to high-precision experiments in neutron beta decay
Experimental demonstration of a universally valid error-disturbance uncertainty relation in spin-measurements
The uncertainty principle generally prohibits determination of certain pairs
of quantum mechanical observables with arbitrary precision and forms the basis
of indeterminacy in quantum mechanics. It was Heisenberg who used the famous
gamma-ray microscope thought experiment to illustrate this indeterminacy. A
lower bound was set for the product of the measurement error of an observable
and the disturbance caused by the measurement. Later on, the uncertainty
relation was reformulated in terms of standard deviations, which focuses solely
on indeterminacy of predictions and neglects unavoidable recoil in measuring
devices. A correct formulation of the error-disturbance relation, taking recoil
into account, is essential for a deeper understanding of the uncertainty
principle. However, the validity of Heisenberg's original error-disturbance
uncertainty relation is justifed only under limited circumstances. Another
error-disturbance relation, derived by rigorous and general theoretical
treatments of quantum measurements, is supposed to be universally valid. Here,
we report a neutron optical experiment that records the error of a
spin-component measurement as well as the disturbance caused on another
spin-component measurement. The results confirm that both error and disturbance
completely obey the new, more general relation but violate the old one in a
wide range of an experimental parameter.Comment: 11 pages, 5 figures, Nature Physics (in press