Ultrathin metasurface produces nets of quantum entangled photons

Researchers at Sandia National Laboratories and the Max Planck Institute have developed a way to produce a net of quantum entangled photons using a far simpler setup than usual. The key is a precisely patterned surface 100 times thinner than paper, which can replace a room full of optical equipment.

Quantum entanglement is the bizarre-sounding phenomenon where two particles can become so entwined that manipulating one will immediately affect its partner, no matter how far apart they may be. This forms the basis for new technologies such as quantum computing and quantum encryption.

The problem is that generating entangled groups of photons can be difficult, and is usually done with large arrays of lasers, specialized crystals and other optical equipment. But Sandia and the Max Planck team have a much simpler setup—a metasurface.

These devices work sort of like lenses, manipulating light that passes through in a very controlled way. But instead of doing so using their curvature and thickness, metasurfaces have been precisely etched with nanoscale structures to alter light according to the task at hand, including trapping atoms, capturing clearer colors in images and even producing holograms. Best of all, metasurfaces can perform these feats in much smaller devices than previous technology.

The team's new meta surface illuminated in green laser light
The team’s new meta surface illuminated in green laser light

Craig Fritz

For this study, the team’s metasurface took the form of an ultrathin glass sheet covered with nanostructures made from the semiconductor material gallium arsenide. When a laser is beamed through the metasurface, some of the photons that emerge on the other side do so in entangled pairs. And not just one pair at a time, but a whole web of entangled photons. This, the team says, normally requires an entire lab full of equipment to achieve.

“It’s quite complicated and a bit difficult when this multi-entanglement needs more than two or three pairs,” said Igal Brener, lead researcher of the study. “These nonlinear metasurfaces essentially accomplish this task in a sample when before it would have required incredibly complex optical setups.”

Being able to induce quantum entanglement in groups of photons at once could have a wide range of applications for quantum computing, encryption, communications and optics. Before that happens, the team says there is still more work to be done to improve the effectiveness of the metasurface.

The research was published in the journal Science.

Source: Sandia Labs

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