Lithium niobate optomechanical crystal*

Lithium niobate (LN) has excellent piezoelectric and electro-optic properties, enabling it as the workhorse material of the essential components for classical communication. Recently LN is also considered for quantum signal transduction and modulation. High-quality LN microring resonator and LN photonic crystal have been demonstrated with quality factor as high as 10⁷ and 10⁵ respectively.
Here we demonstrate 1D LN optomechanical crystals with optical quality factor as high as 300,000, 2 GHz mechanical mode with quality factor as high as 37,000 at 4 Kelvin and zero-point optomechanical coupling rate g/2π ~ 120 kHz. The optomechanical coupling is shown to be tunable down to zero by designing the orientation of the crystal. We further utilize the piezoelectric coupling to drive the mechanical mode directly and optically readout the motion. We identify both the mechanical bandgap and the mechanical modes. The optomechanical coupling and the compatibility of the LN-on-silicon material system with microwave qubits demonstrate the enormous potential of this piezo-optomechanical platform for quantum electro-optic conversion and coupling between microwave nanomechanics and superconducting qubits.