New quantum tool: Experimental realization of neutron helical waves

Holographic approach to generate neutron helical wavefronts that carry a well-defined OAM. (A) SEM images characterizing the lattice of fork dislocation phase gratings used to generate the helical neutron wavefronts. The arrays covered an area of ​​0.5 cm by 0.5 cm and consisted of 6,250,000 individual 1 μm by 1 μm fork phase dislocation arrays that had a period of 120 nm, were 500 nm in height and were separated by 1 μm on each side. Three arrays with topological loads of q=0 (standard network profile), q=3 (shown here), and q=7 were used in the experiment. (B) Each phase grating generates a diffraction spectrum composed of diffraction orders (m) that carry a well-defined OAM value of ℓ = mħq. (C) The far-field intensity is the sum over the signal of all the individual fork dislocation phase gratings. Here is an example of the small angle neutron scattering (SANS) data collected. Credit: Scientists progress (2022). DOI: 10.1126/sciadv.add2002

For the first time in experimental history, researchers at the Institute for Quantum Computing (IQC) have created a device that generates twisted neutrons with a well-defined orbital angular momentum. Previously thought to be an impossibility, this groundbreaking scientific achievement offers researchers an entirely new avenue to study the development of next-generation quantum materials with applications ranging from quantum computing to identifying and solving novel problems in fundamental physics. .

“Neutrons are a powerful probe for the characterization of emerging quantum materials, as they exhibit several unique characteristics,” said Dr. Dusan Sarenac, IQC Research Associate and Technical Lead, Transformative Quantum Technologies at the University of Waterloo. . “They have nanometer-sized wavelengths, electrical neutrality and relatively large mass. These characteristics mean that neutrons can pass through materials that X-rays and light cannot pass through.”

While the methods of experimental production and analysis of orbital angular momentum in photons and electrons are well studied, a device design using neutrons has never been demonstrated so far. Because of their distinct characteristics, researchers had to build new devices and create new methods for working with neutrons.

During their experiments, Dr. Dmitry Pushin, IQC and faculty member of Waterloo’s Department of Physics and Astronomy, and his team constructed microscopic fork-shaped silicon lattice structures. These devices are so tiny that in an area of ​​just 0.5 cm by 0.5 cm there are more than six million individual fork-dislocation phase networks.

When a beam of single neutrons passes through this device, the individual neutrons begin to coil in a corkscrew pattern. After traveling 19 meters, an image of the neutrons was captured using a special neutron camera. The group observed that each neutron had expanded into a donut-shaped signature 10cm wide.

The ring pattern of the propagating neutrons indicates that they were placed in a special helical state and that the group’s grating devices generated neutron beams with quantized orbital angular momentum, the first such experimental achievement.

“Neutrons have been popular in experimental verification of fundamental physics, using all three readily available degrees of freedom: spin, trajectory and energy,” Pushin said.

“In these experiments, our group has enabled the use of orbital angular momentum in neutron beams, which will essentially provide an additional quantized degree of freedom. In doing so, we are developing a toolbox to characterize and examine the complex materials needed to the next generation of quantum devices such as quantum simulators and quantum computers.”

The article Experimental realization of neutron helic waves by Sarenac, Pushin and collaborators from the University of Waterloo, the National Institute of Standards and Technology and the Oak Ridge National Laboratory was recently published in the journal Scientists progress.