Johann Summhammer

Static versus time-dependent absorption in neutron interferometry

Abstract Neutron absorption in one of the two beam paths of a neutron interferometer gives different interference pattern with static and with time-dependent absorption even when the time-averaged absorption is the same. This has been demonstrated by experiment.

Explicit experimental verification of quantum spin-state superposition☆

Abstract An interferometric experiment with polarized neutrons is described that demonstrates the basic principles of coherent spin-state superposition in an explicit way.

Polarized neutron interferometry: A survey

Abstract A brief summarizing review is given of all those neutron interferometric experiments performed hitherto which explicitly use the spin- 1 2 particle properties of the neutron. It covers topics as the verification of the 4π-periodicity of spinors, the cooperative action of nuclear phase shift and spin-rotation on the neutron wave function, the demonstration of the quantum mechanical principles of fermion spin-state superposition and the more recent double resonance experiments where the two interfering beams propagate through spatially separated oscillatory magnetic fields. Finally a proposal will be presented also for a so-called “late-choice” experiment with polarized neutrons.

Reconstruction of the spin state

An ensemble of spin-

A quantum-mechanical description of ion motion within the confining potentials of voltage-gated ion channels

\frac{1}{2}

Colouring the rational quantum sphere and the Kochen-Specker theorem

particles is observed repeatedly using Stern-Gerlach devices with varying orientations. Synthesis of such noncommuting observables is analyzed using the maximum likelihood estimation as an example of quantum-state reconstruction. Repeated incompatible observations represents a new generalized measurement. This idealized scheme will serve for analysis of future experiments in neutron and quantum optics.

Quantum tomography as normalization of incompatible observations

Voltage-gated channel proteins cooperate in the transmission of membrane potentials between nerve cells. With the recent progress in atomic-scaled biological chemistry, it has now become established that these channel proteins provide highly correlated atomic environments that may maintain electronic coherences even at warm temperatures. Here we demonstrate solutions of the Schrödinger equation that represent the interaction of a single potassium ion within the surrounding carbonyl dipoles in the Berneche-Roux model of the bacterial KcsA model channel. We show that, depending on the surrounding carbonyl-derived potentials, alkali ions can become highly delocalized in the filter region of proteins at warm temperatures. We provide estimations on the temporal evolution of the kinetic energy of ions depending on their interaction with other ions, their location within the oxygen cage of the proteins filter region, and depending on different oscillation frequencies of the surrounding carbonyl groups. Our results provide the first evidence that quantum mechanical properties are needed to explain a fundamental biological property such as ion selectivity in transmembrane ion currents and the effect on gating kinetics and shaping of classical conductances in electrically excitable cells.

Factoring and Fourier transformation with a Mach-Zehnder interferometer

We review and extend recent findings of Godsil and Zaks, who published a constructive colouring of the rational unit sphere with the property that for any orthogonal tripod formed by rays extending from the origin of the points of the sphere, exactly one ray is red, one white and one black. They also showed that any consistent colouring of the real sphere requires an additional colour. We discuss some of the consequences for the Kochen-Specker theorem.

Focusing of pulsed neutrons by traveling magnetic potentials

Standard deterministic techniques for quantum state reconstruction, as for example optical homodyne tomography, photon chopping, unbalanced homodyning etc., are based on the deterministic inversion of measured data. Since the frequencies obtained in realistic experiments always differ from probabilities predicted by quantum theory due to fluctuations, imperfections and realistic restrictions, the algorithm of inversion cannot guarantee the positive definiteness of the reconstructed density matrix. Hence the estimation of the noises may appear as doubtful.

Kelvin probe measurements of microcrystalline silicon on a nanometer scale using SFM

AbstractThe scheme of Clauser and Dowling (Phys. Rev. A53, 4587 (1996)) for factoringN by means of an N-slit interference experiment is translated into an experimentwith a single Mach-Zehnder interferometer. With dispersive phase shifters the ra-tio of coherence length to wavelength limits the numbers that can be factored. Aconservative estimate permits N ≈ 10 7 . It is furthermore shown, that sine andcosine Fourier coefficients of a real periodic function can be obtained with such aninterferometer. PACS: 03.65.Bz, 06.50.Mk, 07.60.LyRecently Clauser and Dowling (CD) have shown that factors of an integer Ncan bedetermined by simply measuring the peaks of the intensity distribution on the screenbehind a Young’s N-slit arrangement [1]. This device is distinct from the currently muchdebated proposals for quantum computation, because it does not need the entanglementof several quantal degrees of freedom. Therefore it is very immune against decoherenceand could readily be implemented with present technology. The drawback is that it willnot exhibit the potential increase in computational power characteristic of entanglement.Nevertheless, the work of CD indicates that single particle interference arrangements haveuseful applications beyond physical measurements.The purpose of this note is to point out that the CD-proposal can be translated intoan experiment with only a single Mach-Zehnder interferometer. This will enhance theflexibility ofthis calculational device. A further point isthat a Mach-Zehnder interferomtercan also perform other computations, in particular cosine and sine Fourier transformations.Let us first focus on the work of CD. This proposal shows, that in a suitably chosencentral region on the detection screen behind an N-slit arrangement, all intensity peaks areequal if, and only if, the quantity n≡ λR/a