Photonic crystal cavities based on suspended yttrium iron garnet nanobeams

Hybrid platforms that join light, sound, and spin promise chip\leavevmode\hbox{-}scale quantum transducers and precision sensors. Yttrium iron garnet (YIG) has the right mix of transparency and low magnetic damping, but making suspended nanostructures that confine all three excitations on one chip remains a tough challenge. The authors use focused\leavevmode\hbox{-}ion\leavevmode\hbox{-}beam milling to carve an air\leavevmode\hbox{-}suspended YIG photonic crystal nanobeam that supports a confined optical mode plus colocalized gigahertz mechanical and magnonic modes. This approach opens a route to tunable magneto\leavevmode\hbox{-}optomechanics and, with higher optical quality factors, could underpin efficient microwave-to-optical conversion for integrated quantum networks.