Enhanced generation of angle correlated photon-pairs in nonlinear metasurfaces

We reveal that strongly enhanced generation of photon pairs with narrow frequency spectra and sharp angular correlations can be realised through spontaneous parametric down-conversion in metasurfaces. This is facilitated by creating meta-gratings through nano-structuring of nonlinear films of sub-wavelength thickness to support the extended bound state in the continuum resonances, associated with ultra-high Q-factors, at the biphoton wavelengths across a wide range of emission angles. Such spectral features of photons can be beneficial for various applications, including quantum imaging. Our modelling demonstrates a pronounced enhancement, compared to unpatterned films, of the total photon-pair generation rate normalized to the pump power reaching 1.75 kHz mW(-1), which is robust with respect to the angular bandwidth of the pump, supporting the feasibility of future experimental realisations.

Automated summary

We demonstrate that enhanced generation of photon pairs with narrow frequency spectra and sharp angular correlations can be achieved through spontaneous parametric down-conversion in metasurfaces. This is accomplished by creating meta-gratings through nano-structuring of nonlinear films of sub-wavelength thickness, supporting extended bound state in the continuum resonances with ultra-high Q-factors, at the biphoton wavelengths across a wide range of emission angles. These spectral features of photons have potential benefits for various applications, including quantum imaging.