Nonlinear Metasurfaces for Generating Quantum Light (NoMaGiQ)

• Applicants: Professor Mikhail Belkin, Ph.D.; Professorin Maria Chekhova, Ph.D.
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 568143457

Nonlinear metasurfaces are highly versatile platforms for linear and nonlinear optics, often outperforming their bulk counterparts. Their advantages are: broad bandwidth and ultrafast response, integrability into more complex devices, and multifunctional behavior. Today, nonlinear metasurfaces are finding more and more use in quantum optics. They are employed as linear optical converters of quantum light, and recently also as sources of entangled photons based on spontaneous parametric down-conversion (SPDC). As quantum light sources, state-of-the-art metasurfaces have two main shortcomings: the low efficiency of SPDC and the relatively high level of photoluminescence (PL) noise. These drawbacks limit the applications of nonlinear metasurfaces as quantum light sources: they provide far worse rate and purity of photon pairs than bulk sources, and their efficiency is insufficient for generating squeezed light. In NoMaGiQ, our first aim is to increase the rate of SPDC in metasurfaces by orders of magnitude and simultaneously dramatically reduce the PL rate. To this end, we will optimize the semiconductor nonlinear material composition and growth conditions to balance nonlinearity, pump absorption, and non-radiative recombination rates, choose the crystal orientation of the wafers used for the nonlinear epilayer growth for metasurface fabrication and the geometry of meta-atoms to achieve the highest effective nonlinear response for SPDC while minimizing PL intensity. With a considerably increased SPDC efficiency, we expect to reach the regime of moderate parametric gain, sufficient for the generation of squeezed vacuum, and to obtain quadrature squeezing. This result will be the first observation of squeezed light emitted by a metasurface and it will open a path for generating quantum states beyond photon pairs – for instance, cluster states, - at the nanoscale. Finally, we will demonstrate up-conversion of one of the entangled photons using the same metasurface where the pairs are generated. This result will be the first demonstration of the multi-functional operation of a quantum optical metasurface.

• DFG Programme: Research Grants