Neutron Interferometry Research Articles

Event-based simulation of quantum physics experiments

We review an event-based simulation approach which reproduces the statistical distributions of wave theory not by requiring the knowledge of the solution of the wave equation of the whole system but by generating detection events one-by-one according to an unknown distribution. We illustrate its applicability to various single photon and single neutron interferometry experiments and to two Bell-test experiments, a single-photon Einstein–Podolsky–Rosen experiment employing post-selection for photon pair identification and a single-neutron Bell test interferometry experiment with nearly 100% detection efficiency.

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

For precise measurements with polarised neutrons high efficient spin-manipulation is required. We developed several neutron optical elements suitable for a new sophisticated setup, i.e., DC spin-turners and Larmor-accelerators which diminish thermal disturbances and depolarisation considerably. The gain in performance is exploited demonstrating violation of a Bell-like inequality for a spin-path entangled single-neutron state. The obtained value of S=2.365(13), which is much higher than previous measurements by neutron interferometry, is 28σ above the limit of S=2 predicted by contextual hidden variable theories. The new setup is more flexible referring to state preparation and analysis, therefore new, more precise measurements can be carried out.

Measurement of the Aharonov-Casher geometric phase with a separated-arm atom interferometer

In this letter, we report a measurement of the Aharonov-Casher (AC) geometric phase with our lithium atom interferometer. The AC phase appears when a particle carrying a magnetic dipole propagates in a transverse electric field. The first measurement of the AC phase was done with a neutron interferometer in 1989 by Cimmino et al. [Phys. Rev. Lett. 63, 380 (1989)] and all the following experiments were done with Ramsey or Ramsey-Bordé interferometers with molecules or atoms. In our experiment, we use lithium atoms pumped in a single hyperfine-Zeeman sublevel and we measure the AC-phase by applying opposite electric fields on the two interferometer arms. Our measurements are in good agreement with the expected theoretical values and they also provide a further test of the independence of the AC phase with the atom velocity.

Direct Evidence of Conformational Changes Associated with Voltage Gating in a Voltage Sensor Protein by Time-Resolved X-ray/Neutron Interferometry

The voltage sensor domain (VSD) of voltage-gated cation (e.g., Na+, K+) channels central to neurological signal transmission can function as a distinct module. When linked to an otherwise voltage-insensitive, ion-selective membrane pore, the VSD imparts voltage sensitivity to the channel. Proteins homologous with the VSD have recently been found to function themselves as voltage-gated proton channels or to impart voltage sensitivity to enzymes. Determining the conformational changes associated with voltage gating in the VSD itself in the absence of a pore domain thereby gains importance. We report the direct measurement of changes in the scattering-length density (SLD) profile of the VSD protein, vectorially oriented within a reconstituted phospholipid bilayer membrane, as a function of the transmembrane electric potential by time-resolved X-ray and neutron interferometry. The changes in the experimental SLD profiles for both polarizing and depolarizing potentials with respect to zero potential were found to extend over the entire length of the isolated VSD’s profile structure. The characteristics of the changes observed were in qualitative agreement with molecular dynamics simulations of a related membrane system, suggesting an initial interpretation of these changes in terms of the VSD’s atomic-level 3-D structure.

Investigations of fundamental phenomena in quantum mechanics with neutrons

Neutron interferometer and polarimeter are used for the experimental investigations of quantum mechanical phenomena. Interferometry exhibits clear evidence of quantum-contextuality and polarimetry demonstrates conflicts of a contextual model of quantum mechanics á la Leggett. In these experiments, entanglements are achieved between degrees of freedom in a single-particle: spin, path and energy degrees of freedom are manipulated coherently and entangled. Both experiments manifest the fact that quantum contextuality is valid for phenomena with matter waves with high precision. In addition, another experiment is described which deals with error-disturbance uncertainty relation: we have experimentally tested error-disturbance uncertainty relations, one is derived by Heisenberg and the other by Ozawa. Experimental results confirm the fact that the Heisenberg's uncertainty relation is often violated and that the new relation by Ozawa is always larger than the limit. At last, as an example of a counterfactual phenomenon of quantum mechanics, observation of so-called quantum Cheshire Cat is carried out by using neutron interferometer. Experimental results suggest that pre- and post-selected neutrons travel through one of the arms of the interferometer while their magnetic moment is located in the other arm.

Testing Chameleon Fields with Ultra Cold Neutron Bound States and Neutron Interferometry

Abstract Chameleons can play a role in the recent acceleration of the expansion of the Universe. We present results where chameleon fields modify the terrestrial gravitational potential above a mirror and lead to a small perturbation of the energy levels of the neutrons in experimental setups such as GRANIT in Grenoble. With the current sensitivity, these experiments probe chameleon fields in a large coupling to matter regime. We also comment on the possibility of testing chameleon fields with neutron interferometry.

Direct Evidence of Conformational Changes Associated with Voltage-Gating in a Voltage Sensor Protein by Time-Resolved X-Ray/Neutron Interferometry

Voltage-gated cation (e.g. Na+, K+) channels are central to neurological signal transmission. The mechanism of voltage-gating, namely the coupling of conformational changes in the voltage sensing domain (VSD) in response to depolarizing potentials with respect to the resting transmembrane electric potential, to opening the pore domain (PD) resulting in transmembrane ionic current, remains unresolved. We report the direct measurement of changes in the scattering-length density (SLD) profile of the VSD protein, vectorially-oriented within a reconstituted phospholipid bilayer membrane, as a function of the transmembrane electric potential by time-resolved x-ray and neutron interferometry. The changes in the experimental SLD profiles are predicted by molecular dynamics simulations, thus providing an interpretation in terms of the VSD's atomic-level 3-D structure.

ULS (<b>UL</b>tra-small angle <b>S</b>cattering instrument) and Interference Imaging

The cold neutron beam port C1-3, ULS (ULtra Small angle scattering instrument) has been designed and built for the ultra-small angle scattering using a pair of Si-perfect crystals, neutron interferometry with Si-perfect crystal, double-crystal method to estimate the perfection of crystals. For these years, this beam port is used for the development of neutron interference imaging.

Improved algorithm for processing grating-based phase contrast interferometry image sets

Grating-based X-ray and neutron interferometry tomography using phase-stepping methods generates large data sets. An improved algorithm is presented for solving for the parameters to calculate transmissions, differential phase contrast, and dark-field images. The method takes advantage of the vectorization inherent in high-level languages such as Mathematica and MATLAB and can solve a 16 × 1k × 1k data set in less than a second. In addition, the algorithm can function with partial data sets. This is demonstrated with processing of a 16-step grating data set with partial use of the original data chosen without any restriction. Also, we have calculated the reduced chi-square for the fit and notice the effect of grating support structural elements upon the differential phase contrast image and have explored expanded basis set representations to mitigate the impact.

Fictitious Forces and Simulated Magnetic Fields in Rotating Reference Frames

We show that the Wigner-Bargmann program of grounding nonrelativistic quantum mechanics in the unitary projective representations of the Galilei group can be extended to include all noninertial reference frames. The key concept is the Galilean line group, the group of transformations that ties together all accelerating reference frames, and its representations. These representations are constructed under the natural constraint that they reduce to the well-known unitary, projective representations of the Galilei group when the transformations are restricted to inertial reference frames. This constraint can be accommodated only for a class of representations with a sufficiently rich cocycle structure. Unlike the projective representations of the Galilei group, these cocycle representations of the Galilean line group do not correspond to central extensions of the group. Rather, they correspond to a class of nonassociative extensions, known as loop prolongations, that are determined by three-cocycles. As an application, we show that the phase shifts due to the rotation of Earth that have been observed in neutron interferometry experiments and the rotational effects that lead to simulated magnetic fields in optical lattices can be rigorously derived from the representations of the loop prolongations of the Galilean line group.

Measurement of the total cross sections of ultracold neutrons with noble gases and search for long-range forces

The comparison of results of cross section measurements by the different methods can provide useful information on existence of long-range interaction. The total neutron cross sections of He, Ne, Ar, Kr, and Xe were measured using a method of ultracold neutrons. Measurements with ultra cold neutrons confirm the discrepancy between coherent cross-section of scattering for He measured by a neutron interferometer and scattering cross-section measured by the transmission method. The discrepancy makes up 5.3 standard deviations.

Potential of the neutron Lloyd’s mirror interferometer for the search for new interactions

We discuss the potential of the neutron Lloyd's mirror interferometer in a search for new interactions at small scales. We consider three hypothetical interactions that may be tested using the interferometer. The chameleon scalar field proposed to solve the enigma of accelerating expansion of the Universe produces interaction between particles and matter. The axion-like spin-dependent coupling between neutron and nuclei or/and electrons may cause P- and T-non-invariant interaction with matter. Hypothetical non-Newtonian gravitational interactions mediates additional short-range potential between neutrons and bulk matter. These interactions between the neutron and the mirror of the Lloyd's type neutron interferometer cause phase shift of neutron waves. We estimate the sensitivity and systematic effects of possible experiments.

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

We present experimental evidence of the generation of distinct types of genuine multipartite entanglement between three degrees of freedom (spin, energy and path) within single-neutron quantum systems. This is achieved via the development of new spin manipulation apparatuses for neutron interferometry and the entanglement is detected via appropriately designed and optimized nonlinear witnesses. Via the applied criteria we reveal even finer properties of the type of the genuine multipartite entanglement that is produced in the experiment. In a subsequent analysis we show the extraordinarily high fidelity of the generated entangled states, proving the outstanding level of controllability of these systems.

Relativistic effects in atom and neutron interferometry and the differences between them

In recent years there has been an enormous progress in matter wave interferometry. The Colella- Overhauser-Werner (COW) type of neutron interferometer and the Kasevich-Chu (K-C) atom interferometer, are the prototype of such devices and the issue of whether they are sensitive to relativistic effects has recently aroused much controversy. We examine the question of to what extent the gravitational red shift, and the related twin paradox effect can be seen in both of these atom and neutron interferometers. We point out an asymmetry between the two types of devices. Because of this, the non-vanishing, non-relativistic residue of both effects can be seen in the neutron interferometer, while in the K-C interferometer the effects cancel out, leaving no residue, although they could be present in other types of atom interferometers. Also, the necessary shifting of the laser frequency (chirping) in the atom interferometer effectively changes the laboratory into a free-fall system, which could be exploited for other experiments.

Possible Daily and Seasonal Variations in Quantum Interference Induced by Chern-Simons Gravity

Possible effects of Chern-Simons (CS) gravity on a quantum interferometer turn out to be dependent on the latitude and direction of the interferometer on Earth in orbital motion around the Sun. Daily and seasonal variations in phase shifts are predicted with an estimate of the size of the effects, wherefore neutron interferometry with ~5 m arm length and ~10(-4) phase measurement accuracy would place a bound on a CS parameter comparable to the Gravity Probe B satellite.

The bound coherent neutron scattering lengths of the oxygen isotopes

The technique of neutron interferometry was used to measure the bound coherent neutron scattering length bcoh of the oxygen isotopes 17O and 18O. From the measured difference in optical path between two water samples, either H217O or H218O versus H2natO, where nat denotes the natural isotopic composition, we obtain bcoh,17O = 5.867(4) fm and bcoh,18O = 6.009(5) fm, based on the accurately known value of bcoh,natO = 5.805(4) fm which is equal to bcoh,16O within the experimental uncertainty. Our results for bcoh,17O and bcoh,18O differ appreciably from the standard tabulated values of 5.6(5) fm and 5.84(7) fm, respectively. In particular, our measured scattering-length contrast of 0.204(3) fm between 18O and natO is nearly a factor of 6 greater than the tabulated value, which renders feasible neutron diffraction experiments using 18O isotope substitution and thereby offers new possibilities for measuring the partial structure factors of oxygen-containing compounds, such as water.

Structural Characterization of the Voltage-Sensor Domain and Voltage-Gated K+-Channel Proteins Vectorially Oriented within a Single Bilayer Membrane at the Solid/Vapor and Solid/Liquid Interfaces via Neutron Interferometry

The voltage-sensor domain (VSD) is a modular four-helix bundle component that confers voltage sensitivity to voltage-gated cation channels in biological membranes. Despite extensive biophysical studies and the recent availability of X-ray crystal structures for a few voltage-gated potassium (Kv) channels and a voltage-gate sodium (Nav) channel, a complete understanding of the cooperative mechanism of electromechanical coupling, interconverting the closed-to-open states (i.e., nonconducting to cation conducting) remains undetermined. Moreover, the function of these domains is highly dependent on the physical-chemical properties of the surrounding lipid membrane environment. The basis for this work was provided by a recent structural study of the VSD from a prokaryotic Kv-channel vectorially oriented within a single phospholipid (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)) membrane investigated by X-ray interferometry at the solid/moist He (or solid/vapor) and solid/liquid interfaces, thus achieving partial to full hydration, respectively (Gupta et al. Phys. Rev. E2011, 84, 031911-1-15). Here, we utilize neutron interferometry to characterize this system in substantially greater structural detail at the submolecular level, due to its inherent advantages arising from solvent contrast variation coupled with the deuteration of selected submolecular membrane components, especially important for the membrane at the solid/liquid interface. We demonstrate the unique vectorial orientation of the VSD and the retention of its molecular conformation manifest in the asymmetric profile structure of the protein within the profile structure of this single bilayer membrane system. We definitively characterize the asymmetric phospholipid bilayer solvating the lateral surfaces of the VSD protein within the membrane. The profile structures of both the VSD protein and phospholipid bilayer depend upon the hydration state of the membrane. We also determine the distribution of water and exchangeable hydrogen throughout the profile structure of both the VSD itself and the VSD:POPC membrane. These two experimentally determined water and exchangeable hydrogen distribution profiles are in good agreement with molecular dynamics simulations of the VSD protein vectorially oriented within a fully hydrated POPC bilayer membrane, supporting the existence of the VSD's water pore. This approach was extended to the full-length Kv-channel (KvAP) at a solid/liquid interface, providing the separate profile structures of the KvAP protein and the POPC bilayer within the reconstituted KvAP:POPC membrane.

Event-Based Simulation of Neutron Interferometry Experiments

Event-Based Simulation of Neutron Interferometry Experiments

Particle and/or wave features in neutron interferometry

Neutron interferometry provides a powerful tool to investigate particle and wave features in quantum physics. Single particle interference phenomena can be observed with neutrons and the entanglement of degrees of freedom, i.e., contextuality can be verified and used in further experiments. Entanglement of two photons, or atoms, is analogous to a double slit diffraction of a single photon, neutron or atom. Neutrons are proper tools for testing quantum mechanics because they are massive, they couple to electromagnetic fields due to their magnetic moment, they are subject to all basic interactions, and they are sensitive to topological effects, as well. The 4π-symmetry of spinor wave functions, the spin-superposition law and many topological phenomena can be made visible, thus showing interesting intrinsic features of quantum physics. Related experiments will be discussed. Deterministic and stochastic partial absorption experiments can be described by Bell-type inequalities. Neutron interferometry experiments based on post-selection methods renewed the discussion about quantum non-locality and the quantum measuring process. It has been shown that interference phenomena can be revived even when the overall interference pattern has lost its contrast. This indicates a persisting coupling in phase space even in cases of spatially separated Schrödinger cat-like situations. These states are extremely fragile and sensitive against any kind of fluctuations and other decoherence processes. More complete quantum experiments also show that a complete retrieval of quantum states behind an interaction volume becomes impossible in principle, but where and when a collapse of the wave-field occurs depends on the level of experiment.

Mysterious Quantum Effects Observed with Neutrons

Single-particle interference phenomena can be observed with neutrons, and the "entanglement of degrees of freedom", i.e. the contextuality, can be verified and used in further experiments. Entanglement of two photons or atoms is a complementary situation to the double-slit diffraction of a single photon, neutron, or atom. In this respect, neutrons are proper tools for testing quantum mechanics, because they are massive, they couple to electromagnetic fields due to their magnetic moment, and they are subject to all basic interactions, and they are sensitive to topological effects as well. The4π-symmetry of spinor wave functions, the spin-superposition law, and many topological phenomena can be made visible, which shows interesting intrinsic features of quantum physics. Related experiments will be discussed. Deterministic and stochastic partial absorption experiments can be described by Bell-type inequalities. Recent neutron interferometry experiments based on post-selection methods have renewed the discussion about quantum non-locality and the quantum measuring process. It has been shown that interference phenomena can be revived even when the overall interference pattern has lost its contrast. This indicates a persisting coupling in the phase space even in cases of spatially separated Schrödinger cat-like situations. These states are extremely fragile and sensitive against any kind of fluctuations and other de-coherence processes. More complete quantum experiments also show that a complete retrieval of quantum states behind an interaction volume becomes impossible in principle.