Neutron Interferometry and Optics Facilities

The Neutron Interferometry and Optics Facilities (NIOFs) are the World's premier facilities for neutron interferometry and related optical measurements.  Neutron interferometry utilizes the quantum properties of the neutron to achieve precision not found in other neutron scattering techniques.  Analogous to a Mach-Zehnder interferometer, perfect crystal neutron interferometry separates a neutron beam along two, entangled paths (reference and sample) that are recombined before exiting the device (see Fig. 1). The neutron accumulates a phase as it traverses the interferometer and any difference between the two paths is measured as a phase shift. This phase shift in turn can then be related to the interaction (electric, magnetic, gravitational) or sample (nuclear) being studied. Because the interferometer is sensitive to neutron’s quantum phase and not just the neutron beam intensity, this technique is far more precise than other methods.

The NIST Center for Neutron Research (NCNR) is home to two facilities (designated as NIOF and NIOF-α) using perfect crystal interferometry. The NIOF is focused on making the highest precision measurements possible; while NIOFa is focused on experiments quantum related. The neutron can be entangled using path, spin, orbital angular momentum, and/or energy forming coherent superpositions in a low-noise, simple-to-interpret system and useful in the study of quantum mechanics. Neutron interferometry has been used test the equivalence principle, demonstrate the 4π spinor symmetry, measure non-classical phases, make high-precision measurement of scattering cross sections (an important parameter in nuclear models), demonstrate decoherence free-subspace, perform Cheshire cat experiments, weak measurements, study material structure, and search for beyond the Standard Model physics. The facilities employ several different interferometers (see Fig. 2) to support this wide breadth of applications.

NIOF-α

The Neutron Interferometry and Optics Facility-α was commission back in 2011 with the aim of performing measurements in quantum information science and on quantum materials. A photo of NIOF-α is shown in Figure 3. The facility provides a monochromatic 4.4 Å neutron beam with a sizable 2.2 Å component when there is no Be filter in place. The interferometer rests on an optical table platform supported by rubber padding to reduce vibrations. The facility is more physically accessible than that of NIOF, allowing for more complicated and flexible setups.

NIOF-α Characteristics

Parameter*	Value	Note
Monochromator Type	Pyrolytic Graphite (PG002)
Monochromator Size	40 mm x 50 mm
Monochromator Mosaic	0.5 degree
Neutron Wavelength	4.4 Å	23% 2.2 Å without Be filter
Neutron Flux	3.56E6 n/(cm2 sec)
Crystal Reflections	<111>	+<220> (if using 2.2 Å)
Max. Observed Contrast	30 %
Platform Size	5 ft x 4 ft	1.524 m x 1.219 m
Beam Height relative to Platform	19.75 in	502 cm

Available  Support Equipment:

• Large vacuum chamber with 6-axis control for isolating the experiment from the environment and to eliminate systematic corrections due to air scattering
• Polarizers: W-shaped supermirrors along with ³He filters
• Beryllium filter for eliminating λ  < 4
• Custom vibrationally decoupled cryostat that can cool samples down to 150 mK

NIOF

The larger and older of the two perfect crystal interferometry facilities is distinguishable by the Hutch (see Fig. 4), a large enclosure to eliminate backgrounds and improve phase stability. To provide neutrons to the inside of the Hutch, neutrons are extracted from a dual-crystal parallel-tracking monochromator system. The sensitivity of the apparatus is greatly enhanced by state-of-the-art thermal, acoustical and vibration isolation systems. To reduce vibration, the Hutch is built on its own foundation, separate from the rest of the building. The position of the inner hutch weighting 40,000 kg is maintained to high precision by a computer-controlled feedback system. The result is a facility with exceptional phase stability and high fringe visibility.

Inside the Hutch a granite platform supports interferometer crystal. To preserve the most stable environment, full control of the instrument is done remotely. Because of the extremely good environmental isolation at the facility, several interferometer crystals have displayed contrasts (aka fringe visibility) exceeding 85 %.

Parameter*	Value	Note
1st Monochromator Type	Pyrolytic Graphite (PG002)
1st Monochromator Size	40 mm x 50 mm
1st Monochromator Mosaic	0.5 degree
2nd Monochromator Type	Pyrolytic Graphite (PG002)	Vertically focusing
2nd Monochromator Size	Nine separate 1 cm x 9 cm
2nd Monochromator Mosaic	0.5 degree
Neutron Wavelength	2.0 Å – 3.1 Å	2.71 Å (typical)
Neutron Flux	1.32E5 n/(cm2 sec)
Crystal Reflections	<111> , <220>	<220> (if using 2.2 Å)
Max. Observed Contrast	97 %
Platform Size	6 ft x 4 ft	1.829 m x 1.219 m
Beam Height relative to Platform	15 inches	381 cm

*Note: Changes to the facilities during the 2021-2025 outage may affect these values

FREQUENT AND RECENT COLLABORATORS

Prof. David Cory
University of Waterloo/ Institute for Quantum Computing
dcory [at] uwaterloo.ca (dcory[at]uwaterloo[dot]ca)

Prof. Dmitry A. Pushin
University of Waterloo/ Institute for Quantum Computing
dmitry.pushin [at] uwaterloo.ca (dmitry[dot]pushin[at]uwaterloo[dot]ca)

Prof. Dusan Sarenac
University at Buffalo
dusansar [at] buffalo.edu (dusansar[at]buffalo[dot]edu)

Prof. Albert Young
North Carolina State University
aryoung [at] ncsu.edu (aryoung[at]ncsu[dot]edu)

Fred Wietfeldt
Tulane University
few [at] tulane.edu (few[at]tulane[dot]edu)

RECENT COLLABORATORING INSTITUTIONS

National Institutes of Health
Oak Ridge National Laboratory
Japan Proton Accelerator Research Complex (J-PARC)
RIKEN (Japan)
Institute of Quantum Computing (Canada)
Indiana University
Nagoya University (Japan)
North Carolina State University
Tulane University
University of Maryland
University of North Carolina - Wilmington
University of Waterloo (Canada)
University at Buffalo