Lithium niobate piezo-optomechanical crystals

Abstract

Demonstrating a device that efficiently connects light, motion, and\nmicrowaves is an outstanding challenge in classical and quantum photonics. We\nmake significant progress in this direction by demonstrating a photonic crystal\nresonator on thin-film lithium niobate (LN) that simultaneously supports\nhigh-$Q$ optical and mechanical modes, and where the mechanical modes are\ncoupled piezoelectrically to microwaves. For optomechanical coupling, we\nleverage the photoelastic effect in LN by optimizing the device parameters to\nrealize coupling rates $g_0/2\\pi\\approx 120~\\textrm{kHz}$. An optomechanical\ncooperativity $C>1$ is achieved leading to phonon lasing. Electrodes on the\nnanoresonator piezoelectrically drive mechanical waves on the beam that are\nthen read out optically allowing direct observation of the phononic bandgap.\nQuantum coupling efficiency of $\\eta\\approx10^{-8}$ from the input microwave\nport to the localized mechanical resonance is measured. Improvements of the\nmicrowave circuit and electrode geometry can increase this efficiency and bring\nintegrated ultra-low-power modulators and quantum microwave-to-optical\nconverters closer to reality.\n