An invention in quantum mechanics could revolutionise future computing and encryption technologies, according to a new study.

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 National Laboratories (USA) and the Max Planck Institute for the Science of Light (Germany) 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.

Entangled photons 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.

Scientists have harnessed it to process information in new ways, for example, entanglement helps protect delicate quantum information and correct errors in quantum computing and it 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 Department of Energy Office of Science user facility operated by Sandia and Los Alamos national laboratories. Sandia’s team received funding from the Office of Science, Basic Energy Sciences programme.

Light goes in, entangled photons come out

The new metasurface acts as a doorway to this unusual quantum phenomenon. Scientists shine a laser through the ‘doorway’ and the beam of light passes through an ultrathin sample of glass covered in nanoscale structures made of a common semiconductor material called gallium arsenide.

Igal Brener, Sandia senior scientist and an expert in a field called nonlinear optics, said that it “scrambles all the optical fields” and “occasionally” a pair of entangled photons at different wavelengths emerge from the sample in the same direction as the incoming laser beam.

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

The study 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. But 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.

What is a metasurface?

A metasurface is a synthetic material that interacts with light and other electromagnetic waves in ways conventional materials can’t. According to Brener, commercial industries are 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 revolutionise consumer products.”

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.

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

Brener, who has studied metamaterials for more than a decade, suggested 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.

The research appeared in the journal Science.

Image: Green laser light illuminates a metasurface that is a hundred times thinner than paper, that was fabricated at the Center for Integrated Nanotechnologies. 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