Microwave-to-optical conversion with a gallium phosphide photonic crystal cavity

  1. Simon Hönl,
  2. Youri Popoff,
  3. Daniele Caimi,
  4. Alberto Beccari,
  5. Tobias J. Kippenberg,
  6. and Paul Seidler
Electrically actuated optomechanical resonators provide a route to quantum-coherent, bidirectional conversion of microwave and optical photons. Such devices could enable optical interconnection
of quantum computers based on qubits operating at microwave frequencies. Here we present a novel platform for microwave-to-optical conversion comprising a photonic crystal cavity made of single-crystal, piezoelectric gallium phosphide integrated on pre-fabricated niobium circuits on an intrinsic silicon substrate. The devices exploit spatially extended, sideband-resolved mechanical breathing modes at ∼ 3.2 GHz, with vacuum optomechanical coupling rates of up to g0/2π≈ 300 kHz. The mechanical modes are driven by integrated microwave electrodes via the inverse piezoelectric effect. We estimate that the system could achieve an electromechanical coupling rate to a superconducting transmon qubit of ∼ 200 kHz. Our work represents a decisive step towards integration of piezoelectro-optomechanical interfaces with superconducting quantum processors.