physics Physics is the scientific study of matter, its Elementary particle, fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge whi ...

, a neutron interferometer is an

interferometer Interferometry is a technique which uses the '' interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber opt ...

capable of diffracting

neutron The neutron is a subatomic particle, symbol or , that has no electric charge, and a mass slightly greater than that of a proton. The Discovery of the neutron, neutron was discovered by James Chadwick in 1932, leading to the discovery of nucle ...

s, allowing the wave-like nature of neutrons, and other related phenomena, to be explored.

Interferometry

Interferometry Interferometry is a technique which uses the ''interference (wave propagation), interference'' of Superposition principle, superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important inves ...

inherently depends on the wave nature of the object. As pointed out by de Broglie in his PhD thesis, particles, including

s, can behave like waves (the so-called

wave–particle duality Wave–particle duality is the concept in quantum mechanics that fundamental entities of the universe, like photons and electrons, exhibit particle or wave (physics), wave properties according to the experimental circumstances. It expresses the in ...

, now explained in the general framework of

quantum mechanics Quantum mechanics is the fundamental physical Scientific theory, theory that describes the behavior of matter and of light; its unusual characteristics typically occur at and below the scale of atoms. Reprinted, Addison-Wesley, 1989, It is ...

). The

wave function In quantum physics, a wave function (or wavefunction) is a mathematical description of the quantum state of an isolated quantum system. The most common symbols for a wave function are the Greek letters and (lower-case and capital psi (letter) ...

s of the individual interferometer paths are created and recombined coherently which needs the application of

dynamical theory of diffraction The dynamical theory of diffraction describes the interaction of waves with a regular lattice. The wave fields traditionally described are X-rays, neutrons or electrons and the regular lattice are atomic crystal structures or nanometer-scale mul ...

. Neutron interferometers are the counterpart of X-ray interferometers and are used to study quantities or benefits related to

thermal A thermal column (or thermal) is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example ...

neutron radiation Neutron radiation is a form of ionizing radiation that presents as free neutrons. Typical phenomena are nuclear fission or nuclear fusion causing the release of free neutrons, which then react with nuclei of other atoms to form new nuclides— ...

Applications

In 1975 Werner and Overhauser demonstrated quantum phase shifts on neutron matter waves due to gravity. The interferometer was oriented such that two paths are at different heights in Earth's gravitational field. The interferometer was sufficiently sensitive to detected the phase shift due to different acceleration. The phase shift originates from time-dilation differences along the two paths.

Construction

Like X-ray interferometers, neutron interferometers are typically made from a single large

crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...

silicon Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...

, often 10 to 30 or more centimeters in diameter and 20 to 60 cm or more in length. Modern

semiconductor A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities (" doping") to its crystal structure. When two regions with different doping level ...

technology allows large single-crystal silicon

boules Boules (, ), or ''jeu de boules'', is a collective name for a wide range of games similar to bowls and bocce in which the objective is to throw or roll heavy balls as closely as possible to a small target ball, called the ''jack''. 'Boules' its ...

to be easily grown. Since the boule is a single crystal, the atoms in the boule are precisely aligned, to within small fractions of a

nanometer 330px, Different lengths as in respect to the Molecule">molecular scale. The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm), or nanometer (American spelling Despite the va ...

or an

angstrom The angstrom (; ) is a unit of length equal to m; that is, one ten-billionth of a metre, a hundred-millionth of a centimetre, 0.1 nanometre, or 100 picometres. The unit is named after the Swedish physicist Anders Jonas Ångström (1814–18 ...

, over the entire boule. The interferometer is created by removing all but three slices of silicon, held in perfect alignment by a base. (image) Neutrons impinge on the first slice, where, by

diffraction Diffraction is the deviation of waves from straight-line propagation without any change in their energy due to an obstacle or through an aperture. The diffracting object or aperture effectively becomes a secondary source of the Wave propagation ...

from the crystalline lattice, they separate into two beams. At the second slice, they are diffracted again, with two beams continuing on to the third slice. At the third slice, the beams recombine, interfering constructively or destructively, completing the interferometer. Without the precise, angstrom-level alignment of the three slices, the interference results would not be meaningful.

Cold neutrons

The first neutron interferometer experiments were performed in the 1980s. Experiments with cold neutrons are more recent. Only recently, a neutron interferometer for cold and ultracold neutrons was designed and successfully run. Neutron-optical components in this case comprise three gratings. They are artificially

holograph An autograph or holograph is a manuscript or document written in its author's or composer's hand. The meaning of " autograph" as a document penned entirely by the author of its content (as opposed to a typeset document or one written by a copy ...

ically produced, i.e., by means of a light-optic two-wave interference setup illuminating a photo-neutron-refractive polymer. Mechanical stability and count rates are crucial for such an experiment. Therefore, efficient, thermally and mechanically stable optical devices are needed.

References

{{Reflist * V. F. Sears, ''Neutron Optics'', Oxford University Press (1998). * H. Rauch and S. A. Werner, ''Neutron Interferometry'', Clarendon Press, Oxford (2000). Interferometers

Interferometer Interferometry is a technique which uses the '' interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber opt ...