The quantum mechanical propagator of a massive particle in a linear gravitational potential derived already in 1927 by Kennard [2, 3] contains a phase that scales with the third power of the time T during which the particle experiences the corresponding force. Since in conventional atom interferometers the internal atomic states are all exposed to the same acceleration a, this $$T^3$$ -phase cancels out and the interferometer phase scales as $$T^2$$ . In contrast, by applying an external magnetic field we prepare two different accelerations $$a_1$$ and $$a_2$$ for two internal states of the atom, which translate themselves into two different cubic phases and the resulting interferometer phase scales as $$T^3$$ . We present the theoretical background for, and summarize our progress towards experimentally realizing such a novel atom interferometer.

Neutron interferometry enables precision measurements that are typically operated within elaborate, multi-layered facilities which provide substantial shielding from environmental noise. These facilities are necessary to maintain the coherence requirements in a perfect crystal neutron interferometer which is extremely sensitive to local environmental conditions such as temperature gradients across the interferometer, external vibrations, and acoustic waves. The ease of operation and breadth of applications of perfect crystal neutron interferometry would greatly benefit from a mode of operation which relaxes these stringent isolation requirements. Here, the INDEX Collaboration and National Institute of Standards and Technology demonstrates the functionality of a neutron interferometer in vacuum and characterize the use of a compact vacuum chamber enclosure as a means to isolate the interferometer from spatial temperature gradients and time-dependent temperature fluctuations. The vacuum chamber is found to have no depreciable effect on the performance of the interferometer (contrast) while improving system stability, thereby showing that it is feasible to replace large temperature isolation and control systems with a compact vacuum enclosure for perfect crystal neutron interferometry.

1. Introduction 2. Neutron interferometers and apparatus 3. Neutron interactions and the coherent scattering lengths 4. Coherence and decoherence 5. Spinor symmetry and spin superposition 6. Topological and geometric phases 7. Contexuality and Kochen-Specker phenomena 8. Gravitational, inertial and motional effects 9. Solid state physics applications 10. Forthcoming, proposed and more speculative experiments 11. Perfect crystal neutron optics 12. Interpretational questions and conclusions

We have performed high-precision measurements of the zero-energy neutron scattering amplitudes of gas phase molecular hydrogen, deuterium, and He-3 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)(He)(3) = (5.8572 +/- 10.0072) 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)(He)(3) = (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-(3) He 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. (c) 2006 Elsevier B.V. All rights reserved.

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 bne. 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 bne 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 bne and hence the neutron MSCR.

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 D2O+ZnBr2. 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.

We have performed high precision measurements of the zero-energy neutron scattering amplitudes of gas phase molecular hydrogen, deuterium, and He using neutron interferometry. We find bnp = (−3.7384 ± 0.0020) fm[1], bnd = (6.6649 ± 0.0040) fm[2,1], and bn3He = (5.8572 ± 0.0072) fm[3]. 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: bnp = (−3.7389 ± 0.0010) fm, bnd = (6.6683 ± 0.0030) fm, and bn3He = (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-He 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.

The recently discovered dynamical diffraction effect ‘neutron camel’ was used for residual stress measurements in a thick Si (111) crystal coated with a 2000 Å-thick Ni film. The observed asymmetry of the back-face rocking curve corresponds to the bending radius of ∼19 km and the tension force applied to the Ni film is ∼90 N/m. Relative deformation of the Si crystallographic cells in the vicinity of diffractive surfaces is |∂uz/∂z|≈1.6×10-6.

The low-energy excitations of incommensurate antiferromagnetic Cr have been investigated by means of high-resolution, inelastic neutron scattering with unpolarized, cold neutrons within an energy range E<9 meV. In agreement with previous measurements we observe Fincher–Burke excitations in the transverse spin density wave phase that appear between the unresolved spin-wave peaks at the incommensurate positions Q±=(1±δ,0,0). In contrast to the previous measurements, our high-resolution data shows that the Fincher–Burke modes do not follow a linear dispersion. Therefore, they have nothing in common with the acoustic phonon branch. The major part of the scattering is concentrated in the range 4 meV<E<8 meV.

The interaction of neutrons with matter enables neutron radiography1 to complement X-ray radiography in analysing materials. Here we describe a simple quantitative method that provides a new contrast mechanism for neutron radiography and allows samples to be imaged at low radiation doses. Large phase shifts can be measured accurately from detailed structures not amenable to conventional techniques.

We describe novel, compact optical elements for collimating and/or focusing beams of slow neutrons. These optical elements are solid composites consisting of regular stacks of alternating micro-foils analogous in action to Soller slits. They are made out of pairs of metals with suitable refractive indices for reflection and/or absorption of the radiation. The performance of these proof-in-principle collimating elements is limited only by the choice of microfoil materials and uniformity of their interfaces.