Quantum Mechanics’ Image
In this artist rendering of a metasurface, light passes through tiny, rectangular structures — the building blocks of the metasurface — and creates pairs of entangled photons at different wavelengths. (Image courtesy of Igal Brener)

An ultrathin invention could make future computing, sensing and encryption technologies remarkably smaller and more powerful by helping scientists control a strange but useful phenomenon of quantum mechanics. Scientists at Sandia and the Max Planck Institute for the Science of Light have reported on a device that could replace a roomful of equipment to link 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 particles and other very tiny things.

Although the phenomenon might seem odd, scientists have harnessed it to process information in new ways. For example, entanglement helps protect delicate quantum information and correct errors in quantum computing, a field that could someday have sweeping impacts in areas such as national security, science and finance. Entanglement is also enabling new, advanced encryption methods for secure communication. Research for the groundbreaking device, which is a hundred times thinner than a sheet of paper, was performed, in part, at the Center for Integrated Nanotechnologies, a DOE 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. When 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, he said, a pair of entangled photons at different wavelengths emerge from the sample in the same direction as the incoming laser beam.

Igal 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. Some 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 multiple tables full of lasers, specialized crystals and other optical equipment.

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

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