Efficient bidirectional piezo-optomechanical transduction between microwave and optical frequency

Efficient interconversion of both classical and quantum information between microwave and optical frequency is an important engineering challenge. The optomechanical approach with gigahertz-frequency mechanical devices can be extremely efficient due to the large optomechanical response of common materials and wavelength-scale localization of mechanical energy. However, existing demonstrations suffer from combination of low optical quality factor, low electrical-to-mechanical transduction efficiency, and low optomechanical interaction rate. Here we demonstrate an on-chip piezo-optomechanical transducer that systematically addresses all these challenges to achieve nearly three orders of magnitude improvement in conversion efficiency. Our modulator demonstrates acousto-optic modulation with V_π=0.02 V. We show bidirectional conversion efficiency of 10⁻⁵ with 3.3 μW red-detuned optical pump, and 5.5% with 323 μW blue-detuned pump. Further study at mK temperatures is required to understand how the efficiency and added noise are affected by reduced mechanical dissipation, thermal conductivity and capacity.