  Leveraging the quantum information processing ability of superconducting
circuits and long-distance distribution ability of optical photons promises the
realization of complex and large-scale quantum networks. In such a scheme, a
coherent and efficient quantum transducer between superconducting and photonic
circuits is critical. However, such quantum transducer is still challenging
since the use of intermediate excitations in current schemes introduces extra
noise and limits bandwidth. Here we realize direct and coherent transduction
between superconducting and photonic circuits based on triple-resonance
electro-optics principle, with integrated devices incorporating both
superconducting and optical cavities on the same chip. Electromagnetically
induced transparency is observed, indicating the coherent interaction between
microwave and optical photons. Internal conversion efficiency of 25.9\pm0.3\%
has been achieved, with 2.05\pm0.04\% total efficiency. Superconducting cavity
electro-optics offers broad transduction bandwidth and high scalability, and
represents a significant step towards the integrated hybrid quantum circuits
and distributed quantum computation.
