Metasurface interferometry toward quantum sensors

Optical metasurfaces open new avenues for the precise wavefront control of light for integrated quantum technology. Here, we demonstrate a hybrid integrated quantum photonic system that is capable of entangling and disentangling two-photon spin states at a dielectric metasurface. Via the interference of single-photon pairs at a nanostructured dielectric metasurface, a path-entangled two-photon NOON state with circular polarization that exhibits a quantum HOM interference visibility of 86 ± 4% is generated. Furthermore, we demonstrate nonclassicality andphase sensitivity in a metasurface-based interferometer with a fringe visibility of 86.8 ± 1.1% in the coincidence counts. This high visibility proves the metasurface-induced path entanglement inside the interferometer. Our findings provide a promising way to develop hybrid-integrated quantum technology operating in the high-dimensional mode space in various applications, such as imaging, sensing, and computing.Metasurfaces: An entangled path to hybrid quantum photonic technologiesScientists have developed an optical metasurface capable of entangling and disentangling photon-pairs, providing a path for the development of quantum technologies for applications in computing, imaging, and sensing. Optical metasurfaces are sub-wavelength layers of nanostructures capable of precisely controlling the properties of light. They offer the promise of new miniaturized quantum systems where they remain largely unexplored. Now Thomas Zentgraf and colleagues from the University of Paderborn in Germany, working with researchers from the University of Stuttgart and the Southern University of Science and Technology in China, have developed a nanostructured dielectric metasurface capable of entangling and disentangling the spin states of a photon-pair. Quantum interference of the photons on the metasurface produces a circularly polarized entangled photon-pair, which can be disentangled by passing it through the metasurface a second time.