In this artistic rendering of the metasurface, light passes through the tiny, rectangular structures – the building blocks of the metasurface –and creates pairs of entangled photons at different wavelengths. Image courtesy of Igal Brener, Sandia National Laboratories.
In this artistic rendering of the metasurface, light passes through the tiny, rectangular structures – the building blocks of the metasurface –and creates pairs of entangled photons at different wavelengths. Image courtesy of Igal Brener, Sandia National Laboratories.

An ultrathin invention could make future computing, sensing and encryption technologies smaller and more powerful by helping scientists control a strange but useful phenomenon of quantum mechanics.

In a paper in Science, scientists at Sandia National Laboratories and the Max Planck Institute for the Science of Light in Germany report a novel device for linking photons in a bizarre quantum effect called entanglement. This device – a kind of nano-engineered material called a metasurface – paves the way for entangling photons in complex ways that have not been possible with compact technologies.

When scientists say photons are entangled, they mean they are linked 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 an effect of quantum mechanics, the laws of physics that govern subatomic particles and other very tiny things.

Although the phenomenon might seem odd, scientists have already harnessed it to process information in new ways. For example, entanglement helps to protect delicate quantum information and correct errors in quantum computing, a field that could someday have sweeping impacts in national security, science and finance. Entanglement is also enabling new, advanced encryption methods for secure communication.

Research for the ground-breaking device, which is 100 times thinner than a sheet of paper, was performed, in part, at the Center for Integrated Nanotechnologies, a US Department of Energy Office of Science user facility operated by Sandia and Los Alamos national laboratories.

The new metasurface acts as a doorway to this unusual quantum phenomenon. In some ways, it’s like the mirror in Lewis Carrol’s ‘Through the Looking-Glass’, through which the young protagonist Alice experiences a strange, new world.

Instead of walking through their new device, the scientists shine a laser through it. The beam of light passes through an ultrathin sample of glass covered in nanoscale structures made of a common semiconductor material called gallium arsenide.

“It scrambles all the optical fields,” said Sandia senior scientist Igal Brener, an expert in a field called nonlinear optics who led the Sandia team. Occasionally, a pair of entangled photons at different wavelengths will emerge from the sample in the same direction as the incoming laser beam.

Brener said he is excited about this device because it is designed to produce complex webs of entangled photons — not just one pair at a time but several pairs all entangled together, and some that can be indistinguishable from each other. Certain technologies need these complex varieties of so-called multi-entanglement for sophisticated information-processing schemes.

Other miniature technologies based on silicon photonics can also entangle photons but without the much-needed level of complex multi-entanglement. Until now, the only way to produce such results was with tables full of lasers, specialized crystals and other optical equipment, which can fill a room.

“It is quite complicated and kind of intractable when this multi-entanglement needs more than two or three pairs,” Brener said. “These nonlinear metasurfaces essentially achieve this task in one sample when before it would have required incredibly complex optical setups.”

The Science paper outlines how the team successfully tuned their metasurface to produce entangled photons with varying wavelengths, a critical precursor to generating several pairs of intricately entangled photons simultaneously. However, the researchers note in their paper that the efficiency of their device – the rate at which they can generate groups of entangled photons – is lower than that of other techniques and needs to be improved.

A metasurface is a synthetic material that interacts with light and other electromagnetic waves in ways that conventional materials can’t. According to Brener, commercial industries are busy developing metasurfaces because they take up less space and can do more with light than, for instance, a traditional lens.

“You now can replace lenses and thick optical elements with metasurfaces,” he said. “Those types of metasurfaces will revolutionize consumer products.”

Sandia is one of the leading institutions in the world performing research on metasurfaces and metamaterials. Between its Microsystems Engineering, Science and Applications complex, which manufactures compound semiconductors, and the nearby Center for Integrated Nanotechnologies, researchers have access to all the specialized tools they need to design, fabricate and analyze these ambitious new materials.

“The work was challenging as it required precise nanofabrication technology to obtain the sharp, narrowband optical resonances that seeds the quantum process of the work,” said Sylvain Gennaro, a former postdoctoral researcher at Sandia who worked on several aspects of the project.

The device was designed, fabricated and tested through a partnership between Sandia and a research group led by physicist Maria Chekhova, an expert in the quantum entanglement of photons at the Max Planck Institute for the Science of Light.

“Metasurfaces are leading to a paradigm shift in quantum optics, combining ultrasmall sources of quantum light with far reaching possibilities for quantum-state engineering,” said Tomás Santiago-Cruz, a member of the Max Plank team and first author of the paper.

Brener, who has studied metamaterials for more than a decade, said this newest research could possibly spark a second revolution – one that sees these materials developed not just as a new kind of lens, but as a technology for quantum information processing and other new applications.

“There was one wave with metasurfaces that is already well established and on its way. Maybe there is a second wave of innovative applications coming,” he said.

This story is adapted from material from Sandia National Laboratories, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.