News | June 6, 2018

Can You See The Light? Researchers Reveal Quantum Magnets That Mimic Light

This is a graphical representation of theoretical neutron scattering on a quantum spin ice. Note the characteristic pinch point(circled), a bow-tie shaped pattern of neutron reflection. Image courtesy of OIST

What is light? It seems like a simple question at first sight, but it has kept on captivating the hearts of great scientists for centuries.

With collaborative research by scientists of Okinawa Institute of Science and Technology (OIST), we have made an abstract theory on the quantum properties of magnets a verifiable hypothesis about a new kind of light, A twist was added.

Ever since Isaac Newton refracted light through the prism in 1672, scientists have been divided into particle theories of light as particles and wave theory as waves. Although light travels linearly like particles, Newton's experiment also showed that light has frequency and wavelength as well as acoustic waves as well.

  About two hundred years later, Scottish physicist James Clark Maxwell noticed that light is composed of varying electric and magnetic fields, presenting a new view to elucidate the mystery of light did. Eventually in the 20th century, for the first time by Einstein's research, light is understood to be composed of basic particles called photons that behave like both particles and waves.

Furthermore, this discovery also encouraged new developments in quantum mechanics to explain the behavior of particles and energy at atomic or atomic levels

Furthermore, in recent years in the second half of the 20th century, physicists began exploring the phenomenon "emergence." Emergence means, for example, that there is a large crowd of many people. It is also possible for unpredictable composition to appear due to the behavior of the crowd and the behavior of one of them being different. In this way, emergent research shows the possibility of unpredictable movement by each particle in a large particle group, raising a new perspective on the new physical law and the conventional law constructed by it . And one of the questions asked was "Does emergent light exist?"

Here is Professor Nick Shannon of OIST, Doctoral Student Yang Han belonging to the quantum theory unit led by Professor, and their collaborators in Switzerland and the United States will be on their way. Because their recent research results focus on strange magnetic bodies known as spin ice. This spin ice was completely removed from the conventional magnetic order and opened a new door to the world of quantum physics.

For example, there are general magnets to attach to a refrigerator at home. In order for such magnets to "stick" to metal objects or the like, magnetic atoms in the magnet form a small magnetic field, which cooperate to create a larger magnetic field. In addition, the magnetic force is established by arranging the small magnetic fields due to magnetic atoms to face the same direction.

 On the other hand, in the case of spin ice, a magnetic field that varies at the atomic level is formed by cooperative action, even though the magnetic atoms are not aligned.

 Recently researchers realized that it was possible to introduce an emergent electric field into spin ice by the quantum effect at low temperature, which led to surprising results. The emergent electric field and the magnetic field combine to cause magnetic excitation and they act exactly like photons of light.

"It behaves like light, but you can not see with the naked eye," Professor Shannon says. "Imagine the situation where spin ice crystal is a small universe with its own natural law and you are looking at it from the outside, how can you figure out what is going on inside?" I will.

2012, Owen Benton Dr. was a student of Shannon professor and then PhD, by bouncing neutrons from magnetic atoms in the crystal, a method of detecting the light in the quantum spin ice raised was. Researchers predicted the characteristic traces of how crystals absorb neutron energy and show the existence of emergent electrodynamics in quantum spin ice.

In the paper published in Nature Physics magazine , the authors report that this trace was successfully observed with a substance called praseodymium · hafnate (Pr 2 Hf 2 O 7 ).

To find traces of emergent light with actual materials, it was very difficult to work with cold with impurities or defects and at a low temperature of 50 milli Kelvin (absolute zero to less than 0.1 degrees)

The research team of Dr. Romaine Sybil of Switzerland's Paul Scherrer Institute (PSI) worked with researchers at Warwick University in the UK to finally complete the quantum spin ice material that can verify this hypothesis We succeeded in making crystals.

Professor Shannon said, "It is a very beautiful material like a precious stone," he said, "It is also amazing to be one big perfect crystal."

Dr. Sybil brought this crystal to Laue-Langevin Institute (ILL) in Grenoble city, France and Oak Ridge National Laboratory (ORNL) in Tennessee, USA, and the specially developed neutron spectrometer We used

In an experiment with great difficulty, Dr. Sybil 's team succeeded in selectively reflecting different types of neutrons by using a row of 960 super mirrors coated with iron, cobalt, or vanadium did. Several of the supermirrors were developed by PSI belonging to Dr. Civil and HYSPEC instrument (ORNL) was used to perform 3D analysis of the reflection pattern

We were able to measure the polarization of the scattered particles through the mapping of the scattered neutrons obtained from IN5 and succeeded in mapping the traces of energy generated from those particles

As a result, the theory of Dr. Benton and Professor Shannon was surprisingly similar to the energy diagram obtained in the experiment (see above figure). In the energy diagram imaging this neutron reflex, we saw the so-called "pinch point" (a structure whose center is constricted like a bow tie), which is a feature of quantum spin ice. And as spin ice was scanned at low temperature, these pinch points disappeared as strongly suggesting the emergence of emergent light.

Mr. Yang Han of the same research team measured the speed of emergent light by analyzing experimental data while working on the theory of this phenomenon. The speed is modest at 3.6 meters per second, which is about as fast as finishing a marathon in four hours. By the way, photons of light that we take sunbathing etc. run the same distance less than 0.001 seconds.

"This substance acts like a microcosm with unique light and charged particles, but I think it is wonderful," Han said.

"At this time, there is no known way to explain these results without using quantum mechanics, so we can say that we actually showed the existence of emergent light. "Professor Shannon said.

Source: Okinawa Institute of Science and Technology (OIST)