Neutron Interferometry Research Articles

Neutron Optics and Physics Beamline (J-PARC BL05)

A pulsed cold neutron beam for the study of neutron optics and fundamental physics (NOP) is under construction as the BL05 of the spallation neutron source of the J-PARC. The NOP beamline has three beam branches, which provide the highly-polarized beam, high intensity beam and low divergence beam for the neutron decay experiment, the neutron scattering experiment and the neutron interferometry experiment, respectively. We overview the physics to be studied at the NOP beamline at its beginning stage.

Perfect crystal neutron interferometry and tensorial neutron tomography

Perfect crystal neutron interferometry may be applied in the tomographic study of magnetic structures in ferromagnetic solids. As a result of such investigations one can expect a complete 3D representation of the magnetisation distribution inside the sample. While the concept is comparable to absorption and phase contrast tomography, the tensorial technique involves 3D polarisation control and specific reconstruction algorithms due to path-ordering effects contained in the measured projections. We present the current status of related methodical development and outline the experimental and technical requirements essential for the application of this method. A 2D reconstruction example is given for a standardised simulated test sample using a reconstruction algorithm based on elimination of path-ordering effects by measurements at different neutron velocities.

Reciprocal space approaches to neutron imaging

Here the authors introduce a Fourier based method for phase contrast neutron imaging, report its experimental implementation, and show results for a one-dimensional test phantom. This approach makes use of neutron interferometry to achieve both phase contrast and to spatially code the phase of the neutron with a linear phase grating. The spatial information is recovered from the coherent interference of this phase grating and a spatial phase distribution due to the sample. By moving neutron imaging from real to reciprocal space they avoid the need for position sensitive detectors and improve the potential image resolution.

Reconstruction techniques for tensorial neutron tomography

The development of techniques to determine the magnetic structure of ferromagnetic materials is still an issue for basic research. We present in this contribution methods for tomographic reconstruction of magnetic domains in bulk material by means of polarized neutrons. The effect of magnetic fields on the neutron wave function while traversing a ferromagnetic sample is described by means of path ordered integrals. Such integrals may be determined experimentally in neutron depolarization or neutron interferometer measurements. Application of inverse Radon transformation used in standard tomography does not yield acceptable results for large rotation angles of the neutron polarization vector, due to path-ordering effects. Recently we have developed algorithms which take these effects specifically into account. The best reconstruction results were so far obtained by a modified algebraic reconstruction technique. We present the quality of reconstruction results for a simulated ferromagnetic test sample. These methods are particularly attractive since they result in a direct 3D visualization of the spatial magnetization distribution in bulk material.

Neutron interferometric method to provide improved constraints on non-Newtonian gravity at the nanometer scale

In recent years, an energetic experimental program has set quite stringent limits on a possible ``non-$1/{r}^{2}$'' dependence on gravity at short length scales. This effort has been largely driven by the predictions of theories based on compactification of extra spatial dimensions. It is characteristic of many such theories that the strength and length scales of such anomalous gravity are not clearly determined from first principles. As a result, it is productive to extend the current limits the range and strength of such hypothetical interactions. As a heavy, neutral, and (almost) stable particle, the neutron provides an ideal probe for the study of such hypothetical interactions at very short range. In this work, we describe methods based on neutron interferometry which have the capability to provide improved sensitivity non-Newtonian forces down to length scales at and below an nanometer.

Quantum Contextuality in a Single-Neutron Optical Experiment

An experimental demonstration of quantum contextuality with neutrons is presented, which intended to exhibit a Kochen-Specker-like phenomenon. Since no perfect correlation is expected in practical experiments, inequalities are derived to distinguish quantitatively the obtained results from predictions by a noncontextual hidden variable theory. Experiments were accomplished with the use of a neutron interferometer combined with spinor manipulation devices. The results clearly violate the prediction of noncontextual theories.

Decoherence Modes in Neutron Interferometry

We give a short introduction to the topics of decoherence, neutron interferometry and entanglement for single neutrons. We introduce two theoretical modes of decoherence for an entangled two qubit system via special Lindblad generators for the quantum master equation. The experimental realization of the decoherence modes is achieved within neutron interferometry where the decoherence is modeled by fluctuating magnetic fields in the interferometer.

Concluding remarks: Thirty years of neutron interferometry

The quantum interference of neutron deBroglie waves extending over macroscopic distances is one of the most startling and fundamental realizations of the predictions of quantum mechanics. Because the neutron experiences all four basic forces of nature (strong, weak, electromagnetic and gravitational), neutron interferometry has proven to be a broad and fertile testing ground for theory. Since the earliest experiments in Vienna, Ann Arbor and Grenoble, there have been at least 50 neutron interferometry experiments which can be said to test and elucidate the fundamental fabric of physics. It has been a great pleasure for me to have been a part of this field for the past three decades, and to have had so many wonderful students and collaborators around the world. Indeed, it is an honor to thank them all at this conference.

Gravitationally induced quantum interference using a floating interferometer crystal

Since the first observation of the phase shift of a neutron de Broglie wave induced by Earth's gravity, a series of increasingly sophisticated and precise experiments were carried out at the University of Missouri Research Reactor over a period of 1980–1997, now collectively called COW experiments. This class of neutron experiments is unique in that it represents a test of the principle of equivalence on a microscopic scale and that the outcome depends upon both the gravitational acceleration g and Planck's constant h. After all these efforts, however, there is still a 0.6–0.8% discrepancy between theory and experiment. The main correction is due to the bending of the interferometer crystal blades. The goal of this new attempt is to eliminate this effect by performing a gravitationally induced quantum interference experiment with a floating interferometer crystal. This means that the crystal is immersed in a liquid of equal density, i.e. a mixture of D 2O+ZnBr 2. The experiment will be carried out at the Neutron Interferometer and Optics Facility of the National Institute of Standards and Technology. This paper will give an overview of the previous experiments and present the experimental technique of the floating COW experiment.

Phase imaging with thermal neutrons

Across four decades, Sam Werner has built and performed elegant neutron interferometry experiments to measure a variety of quantum mechanical phases. These experiments have stringent requirements on experimental conditions and neutron beam conditioning. However, since refractive variations within a sample redistribute neutron intensity transverse to the propagation direction, a simple experimental geometry permits non-interferometric phase measurement and relaxes beam-conditioning requirements. This phase imaging technique, based on the transport of intensity equation, has advantages of allowing weakly absorbing samples to be radiographed at greatly reduced radiation doses, and enabling the use of polychromatic neutrons to increase flux and speed imaging. Furthermore, using other radiations, phase vortices like those of the Aharonov–Bohm effects have been observed.

Consequences of dynamical diffraction and the Sagnac effect in LLL perfect single crystal interferometers

The LLL perfect single crystal interferometer is an exciting tool for exploring a variety of topics of fundamental importance in understanding quantum mechanics and for precision measurement of neutron scattering lengths. One of the limiting factors in many neutron interferometry experiments is the overall size of the interferometer. Hence, ever-larger interferometers would seem to be preferable. However, the theory of dynamical diffraction predicts that neutrons that nearly but not exactly satisfy the Bragg condition take different trajectories through a crystal, giving rise to multiple mutually interfering wavefunctions that all contribute to the measurement of an interferogram. This complexity results in shifts in the measured phase difference and a loss of contrast of the interferogram in the presence of potentials which are dependent on the spatial differences between the trajectories of the neutron through the interferometer. This effect has already been experimentally verified for the gravitational potential. Here we discuss the similar effects of dynamical diffraction on the phase shift due to the Sagnac effect and their consequences on the observable contrast in large-scale interferometers.

Reciprocal space neutron imaging

Here we introduce a new method for coherent, reciprocal space neutron imaging. This new method overcomes the limitations of existing neutron imaging methods due to the resolution of the position sensitive detectors. The method implements a spatial encoding similar to that used in nuclear magnetic resonance (NMR) imaging or neutron Fourier spectroscopy. Spatial information is encoded in the phase of neutrons. In this paper we develop the theory, present preliminary results obtained by applying and refocusing a spatial phase gradient on the neutron beam and show simulations based on the experimental parameters of the neutron interferometer setup at the National Institute of Standards and Technology (NIST).

Quantum contextuality in neutron interferometer experiments

Non-local correlations between sufficiently separated subsystems have been extensively discussed. Such a non-locality can be interpreted as a consequence of the correlation between commuting observables. A more general concept, i.e., contextuality, compared to non-locality can be introduced to describe striking phenomena predicted by quantum theory. As the first example, we report a neutron interferometer experiment, where the spin and the path degrees of freedom are used to exhibit the clear violation of a Bell-like inequality. Other aspects of the quantum contextuality is presented, e.g., a flavor of Kochen–Specker-like contradiction in neutron optical experiments, in addition to the quantum state tomography of the Bell-states which are used in the experiments.

Hidden observables in neutron quantum interferometry

Neutron interferometry using monolithic perfect single crystals has become an important tool for fundamental, nuclear, and solid-state physics research. New features of quantum mechanics become measurable by means of neutron interferometry. Such features are quantum phases, which provide a more direct access to properties of wave functions and permit wave function reconstruction, and wave function engineering. Most recently, new experiments concerning off-diagonal and non-cyclic geometrical phases, confinement induced phases, and contextuality related experiments have been performed. These experiments show an intrinsic entanglement of different degrees of freedom of a single particle. Proper post-selection experiments yield to more quantum complete experiments and may help to make quantum mechanics less mystic. Unavoidable quantum losses may play an important role to explain the transition from the quantum to the classical world. All these investigations concern the heart of quantum mechanics and demonstrate the non-local feature of this theory.

Progress towards a high-precision Aharonov–Casher experiment with neutrons highlighting its topological nature

A neutral magnetic dipole diffracting around a lineal charge distribution experiences a force-free interaction and undergoes a phase shift as predicted by Aharonov and Casher [Phys. Rev. Lett. 53 (1984) 319]. The experiment performed by the Melbourne–Missouri collaboration [A. Cimmino, G.I. Opat, A.G. Klein, H. Kaiser, S.A. Werner, M. Arif, R. Clothier, Phys. Rev. Lett. 63 (1989) 380] confirmed the effect in sign and magnitude using a neutron interferometer. Higher accuracy has since been claimed by other groups using atom interferometry, based on the three orders of magnitude larger value of the Bohr magneton compared with the nuclear magneton. However, the geometry of these experiments does not reproduce the essential topological nature of the effect as in our experiment with neutrons. We describe a larger neutron interferometer designed to increase the size of the effect and a reconfigurable electrode assembly simulating a lineal charge distribution movable within the interference loop.

Inertia of intrinsic spin

The state of a particle in space and time is characterized by its mass and spin, which therefore determine the inertial properties of the particle. The coupling of intrinsic spin with rotation is examined and the corresponding inertial effects of intrinsic spin are studied. An experiment to measure directly the spin–rotation coupling via neutron interferometry is analyzed in detail.

Precision neutron interferometric measurements of the n–p, n–d, and n– 3He zero-energy coherent neutron scattering amplitudes

We have performed high-precision measurements of the zero-energy neutron scattering amplitudes of gas phase molecular hydrogen, deuterium, and 3He using neutron interferometry. We find b np = ( - 3.7384 ± 0.0020 ) fm [K. Schoen, D.L. Jacobson, M. Arif, P.R. Huffman, T.C. Black, W.M. Snow, S.K. Lamoreaux, H. Kaiser, S.A. Werner, Phys. Rev. C 67 (2003) 044005], b nd = ( 6.6649 ± 0.0040 ) fm [T.C. Black, P.R. Huffman, D.L. Jacobson, W.M. Snow, K. Schoen, M. Arif, H. Kaiser, S.K. Lamoreaux, S.A. Werner, Phys. Rev. Lett. 90 (2003) 192502, K. Schoen, D.L. Jacobson, M. Arif, P.R. Huffman, T.C. Black, W.M. Snow, S.K. Lamoreaux, H. Kaiser, S.A. Werner, Phys. Rev. C 67 (2003) 044005], and b n 3 He = ( 5.8572 ± 0.0072 ) fm [P.R. Huffman, D.L. Jacobson, K. Schoen, M. Arif, T.C. Black, W.M. Snow, S.A. Werner, Phys. Rev. C 70 (2004) 014004]. When combined with the previous world data, properly corrected for small multiple scattering, radiative corrections, and local field effects from the theory of neutron optics and combined by the prescriptions of the particle data group, the zero-energy scattering amplitudes are: b np = ( - 3.7389 ± 0.0010 ) fm , b nd = ( 6.6683 ± 0.0030 ) fm , and b n 3 He = ( 5.853 ± .007 ) fm . The precision of these measurements is now high enough to severely constrain NN few-body models. The n–d and n– 3He coherent neutron scattering amplitudes are both now in disagreement with the best current theories. The new values can be used as input for precision calculations of few body processes. This precision data is sensitive to small effects such as nuclear three-body forces, charge-symmetry breaking in the strong interaction, and residual electromagnetic effects not yet fully included in current models.

Neutron interferometry: The pioneering contributions of Samuel A. Werner

In 1975, Sam Werner, while on the staff of the Scientific Laboratory of the Ford Motor Company, and his collaborators from Purdue University, Roberto Colella and Albert Overhauser, carried out one of the pioneering experiments in neutron interferometry at the 2 MW University of Michigan research reactor. It was the famous COW Experiment [Colella et al., Phys. Rev. Lett. 34 (1975) 1472] on gravitationally induced quantum interference. Shortly thereafter he moved to the University of Missouri in Columbia, to set up a program of neutron scattering research, including neutron interferometry. In the 25 years until his retirement a large number of beautiful experiments have been performed by Sam, with his group, his numerous students and many international collaborators. This work and its history are briefly reviewed in this paper.

Measuring the neutron's mean square charge radius using neutron interferometry

The neutron is electrically neutral, but its substructure consists of charged quarks so it may have an internal charge distribution. In fact it is known to have a negative mean square charge radius (MSCR), the second moment of the radial charge density. In other words the neutron has a positive core and negative skin. In the first Born approximation the neutron MSCR can be simply related to the neutron–electron scattering length b ne . In the past this important quantity has been extracted from the energy dependence of the total transmission cross-section of neutrons on high-Z targets, a very difficult and complicated process. A few years ago S.A. Werner proposed a novel approach to measuring b ne from the neutron's dynamical phase shift in a perfect crystal close to the Bragg condition. We are conducting an experiment based on this method at the NIST neutron interferometer which may lead to a five-fold improvement in precision of b ne and hence the neutron MSCR.

Decoherence modes of entangled qubits within neutron interferometry

We study two different decoherence modes for entangled qubits by considering a Liouville--von Neumann master equation. Mode A is determined by projection operators onto the eigenstates of the Hamiltonian and mode B by projectors onto rotated states. We present solutions for general and for Bell diagonal states and calculate for the latter the mixedness and the amount of entanglement given by the concurrence. We propose a realization of the decoherence modes within neutron interferometry by applying fluctuating magnetic fields. An experimental test of the Kraus operator decomposition describing the evolution of the system for each mode is presented.