Scientists at Sandia National Labora­tories and the Max Planck Institute for the Science of Light have created a device that could replace a roomful of equipment to produce entangled photon-pairs. An ultrathin meta­surface made of gallium arsenide paves the way for entangling photons in complex ways that have not been possible with compact techno­logies.

“It scrambles all the optical fields,” said Sandia senior scientist Igal Brener. Occa­sionally, he said, a pair of entangled photons at different wavelengths 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. Some technologies need these complex varieties of 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,” Brener said. “These nonlinear meta­surfaces essen­tially achieve this task in one sample when before it would have required incredibly complex optical setups.”

For this result, 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 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. 

Commercial industries, said Brener, 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,” Brener said. “Those types of metasurfaces will revo­lutionize consumer products.”

“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. 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 in Germany. “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-Planck team.

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. (Source: Sandia Nat. Lab)

Reference: T. Santiago-Cruz et al.: Resonant metasurfaces for generating complex quantum states, Science 377, 991 (2022); DOI: 10.1126/science.abq8684

Link: Quantum Radiation, Max Planck Institute for the Science of Light, Erlangen, Germany • Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, USA