One of the Most Strangest and Most Useful Phenomena in Quantum Mechanics is Triggered by a New Invention

One of the Most Strangest and Most Useful Phenomena in Quantum Mechanics is Triggered by a New Inven ...

Light passes through tiny, rectangular structures — the main building blocks of the metasurface — and creates pairs of entangled photons at different wavelengths in this artist's rendering of a metasurface. Credit: Igal Brener, Sandia National Laboratories

An ultrathin invention might make future computing, sensing, and encryption technologies remarkably smaller and more powerful, according to new research recently published in the journal Science.

According to scientists at Sandia National Laboratories and the Max Planck Institute for the Science of Light, this device might replace a roomful of equipment that binds photons in a strange quantum effect called entanglement. It is a kind of nano-engineered material called a metasurface that opens the way for entangling photons in complex ways that have not previously been feasible with compact methods.

Photons are entangled in such a way that actions on one affect the other, no matter where or how far apart the photons are in the universe. It is a scary effect of quantum mechanics, the physics that governs particles and other very tiny things.

CINT is jointly operated by Sandia and Los Alamos national laboratories for the Department of Energy Office of Science. Credit: Craig Fritz, Sandia National Laboratories

Although the phenomenon may seem bizarre, scientists have harnessed it to manipulate information in new ways. For example, entanglement helps protect sensitive quantum information and correct errors in quantum computing, a field that may someday have profound implications for science, finance, and national security. Entanglement is also enabling advanced new encryption methods for secure communication.

Sandia and Los Alamos national laboratories engaged in part of research for the revolutionary device, which is a hundred times smaller than a sheet of paper.

The new metasurface acts as a portal to this unusual quantum phenomenon. In some ways, it's like the mirror in Lewis Carroll's "Through the Looking-Glass," through which the young protagonist Alice encounters a strange, new world.

Scientists emit a laser through a glass sample that is coated in nanoscale structures made of a common semiconductor material called gallium arsenide rather than walking through it.

"It scrambles all the optical fields," said Sandia senior scientist Igal Brener, who is an expert in a field called nonlinear optics and headed the Sandia research group. Occasionally, he said, a pair of entangled photons from different wavelengths emerge from the sample in the same direction as the incoming laser beam.

Igal Brener, a senior scientist at Sandia National Laboratories, led a team that demonstrated a device that is paveing the way for powerful, compact quantum information processing techniques.

Brener said he is a fan of this device because it is capable of assembling complex webs of entangled photons. Instead of just one pair at a time, it can produce many pairs, some of which are undistinguishable from each other in some advanced information processing techniques.

Although other miniature technologies based on silicon photonics can also entangle photons, they lack the necessary degree of complex, multi-entanglement. Until now, the only way to obtain such results was with multiple tables full of lasers, special crystals, and other optical equipment.

When a multi-entanglement requires more than two or three pairs, it is quite difficult and frustrating," Brener said. "These nonlinear metasurfaces effectively accomplish this task in one sample, when previously it would have required enormously complex optical setups."

The Science paper explains how the team manipulated their metasurface to obtain entangled photons with varying wavelengths. This was a crucial prerequisite to generating several pairs of intricately entangled photons simultaneously.

However, the scientists note in their research that their method — the rate at which they can generate groups of entangled photons — is lower than that of other techniques and will require improvements.

A metasurface is a synthetic material that interacts with light and other electromagnetic waves in ways that conventional materials cannot. Commercial industries are busy developing metasurfaces because they take up less space and can do more with light than, for example, a traditional lens.

“You now can substitute lenses and thick optical elements with metasurfaces,” Brener said. “Those kinds of metasurfaces will revolutionize consumer goods.”

Sandia is one of the world's leading research organizations in the areas of metasurfaces and metamaterials. Between its Microsystems Engineering, Science and Applications complex, which produces compound semiconductors, and the nearby Center for Integrated Nanotechnologies, scientists have access to all the expertise they need to design, fabricate, and analyze these ambitious new materials.

"The research was difficult because it required precise nanofabrication techniques to obtain the sharp, narrowband optical resonances that underlie the quantum process of the work," said Sylvain Gennaro, a former postdoctoral researcher at Sandia who participated in several aspects of the project.

Sandia and a research group headed by physicist Maria Chekhova designed and built the device. She is a professor at the Max Planck Institute for the Science of Light.

Tomás Santiago-Cruz, a member of the Max Plank team, is leading to a paradigm shift in quantum optics, by combining ultrasmall quantum light sources with far-reaching quantum state engineering.

Brener, who has studied metamaterials for more than a decade, believes it is possible to start a second revolution, one that sees these materials developed not just as a new lens, but as a technology for quantum information processing and other new applications.

"There was a one wave of metasurfaces that was already well established and on the way." Perhaps a second wave of inventive applications will emerge, according to the researcher.

Tomás Santiago-Cruz, Sylvain D. Gennaro, Oleg Mitrofanov, Sadhvikas Addamane, John Reno, Igal Brener, and Maria V. Chekhova, science. DOI: 10.126/science.abq8684

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