Wavelength alignment of optomechanical crystals for operation at cryogenic temperatures

Piezo-optomechanical crystals (POMCs) are a promising platform for transducing quantum signals between microwave and optical frequencies, enabling quantum networks of distant superconducting microwave circuits via optical links. Achieving remote entanglement in such networks requires wavelength-degenerate optical photons, demanding precise alignment of POMC optical resonances at cryogenic temperatures. However, fabrication-induced disorder causes inhomogeneous optical wavelengths. We address this with a post-fabrication tuning method based on atomic force microscope nano-oxidation, using a calibration protocol that accounts for various factors affecting the wavelength shift from room to cryogenic temperatures. Our technique allows wavelength tuning of POMC at room temperature, achieving up to 6nm tuning around 1550nm for precise alignment at 10mK. This technique can serve as a valuable tool for POMC transducers towards optically-mediated entanglement in superconducting circuits.