Nanomechanical coupling between microwave and optical photons

A variety of nanomechanical systems can now operate at the quantum limit1–4, making quantum phenomena more accessible for applications and providing new opportunities for exploring the fundamentals of quantum physics. Such mechanical quantum devices offer compelling opportunities for quantum-enhanced sensing and quantum information5–7. Furthermore, mechanical modes provide a versatile quantum bus for coupling hybrid quantum systems, supporting a quantum-coherent connection between different physical degrees of freedom8–13. Here, we demonstrate a nanomechanical interface between optical photons and microwave electrical signals, using a piezoelectric optomechanical crystal. We achieve coherent signal transfer between itinerant microwave and optical fields by parametric electro-optical coupling using a localized phonon mode. We perform optical tomography of electrically injected mechanical states and observe coherent interactions between microwave, mechanical and optical modes, manifested as electromechanically induced optical transparency. Our on-chip approach merges integrated photonics with microwave nanomechanics and is fully compatible with superconducting quantum circuits, potentially enabling microwave-to-optical quantum state transfer, and photonic networks of superconducting quantum bits14–16. In engineered quantum systems, the interactions between different physical degrees of freedom can be strongly enhanced by mode confinement in nanoscale structures. In the field of optomechanics17, this has recently enabled quantum-coherent coupling between optical and mechanical modes, and quantum control of mechanical motion2–4. The emerging possibility of mechanically mediated state transfer11,18–22 promises a new type of quantum transducer, using nanomechanical motion to translate electrical or spin-based quantum states to photonic states, thereby creating an optical quantum interface. Here, we present a nanomechanical transducer in which a purpose-designed microwave-frequency mechanical mode generates a coupling between electrical signals at 4GHz and optical photons at 200 THz. Strong coherent interactions between the electrical, mechanical and optical modes are enabled by combining electromechanical and optomechanical coupling in a piezoelectric optomechanical crystal. Fabricated from aluminium nitride (AlN) and monolithically integrated on-chip, the transducer is fully compatiblewith superconducting quantumcircuits and is well suited for cryogenic operation. Operating at microwave mechanical frequencies, this device in principle allows quantum ground-state control of the mechanical mode1 and state transfer between quantum microwave and optical channels. The transducer is illustrated in Fig. 1. A mechanically suspended beamofAlN (0.33×1×100 μm3) is patterned as an optomechanical crystal, designed to support a highly localized phonon mode