physics Physics is the natural science that studies matter, its 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 which r ...

, 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 op ...

capable of diffracting

neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons beh ...

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

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 every particle or quantum entity may be described as either a particle or a wave. It expresses the inability of the classical concepts "particle" or "wave" to fully describe the ...

, now explained in the general framework of

quantum mechanics Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistry, ...

). The

wave function A wave function in quantum physics is a mathematical description of the quantum state of an isolated quantum system. The wave function is a complex-valued probability amplitude, and the probabilities for the possible results of measurements mad ...

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 isotopes— ...

Applications

Neutron interferometers are used to determine minute quantum-mechanical effects on the neutron wavefunction, such as studies of the Aharonov–Bohm effect,

gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...

acting on an elementary particle, the neutron, rotation of the earth acting on a quantum system and they can be applied for neutron phase imaging, and tests of the

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 with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic tab ...

, 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 which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...

technology allows large single-crystal silicon

boules ''Boules'' () is a collective name for a wide range of games similar to bowls and bocce (In French: jeu or jeux, in Croatian: boćanje and in Italian: gioco or giochi) in which the objective is to throw or roll heavy balls (called in France, ...

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 molecular scale. The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm) or nanometer (American and British English spelling differences#-re ...

or an

angstrom The angstromEntry "angstrom" in the Oxford online dictionary. Retrieved on 2019-03-02 from https://en.oxforddictionaries.com/definition/angstrom.Entry "angstrom" in the Merriam-Webster online dictionary. Retrieved on 2019-03-02 from https://www.m ...

, 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 defined as the interference or bending of waves around the corners of an obstacle or through an aperture into the region of geometrical shadow of the obstacle/aperture. The diffracting object or aperture effectively becomes a s ...

from the

crystalline lattice 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 ...

, 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 neutron The neutron detection temperature, also called the neutron energy, indicates a free neutron's kinetic energy, usually given in electron volts. The term ''temperature'' is used, since hot, thermal and cold neutrons are Neutron moderator, moderate ...

s 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 copyist o ...

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 op ...